Koch; Large-Scale Neuronal Theories of the Brain
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Domasio; Convergence Zone 66 Conjoining of nonverbal and verbal activated representations pertaining to concrete entities depends on a mediator mechanism in left anterior temporal cortices. The mechanism promotes the reconstruction of a word form given the concept, or, conversely, the reconstruction of the concept of an object given the word form.
Domasio; Convergence Zone 67 Mediational mechanism for words and concepts do not contain records for either words or concepts themselves but rather records of the probable combination between them. 1
Domasio; Convergence Zone 68 Access to concrete knowledge of higher hierarchical status requires structures in anterior temporal cortices, whereas access to concrete knowledge of lower complexity only requires posterior occipital cortices.  1
Domasio; Convergence Zone 68 Because of cerebral hemisphere dominance effects, certain types and levels of knowledge may require an anterior or intermediate cortex of one hemisphere only. 0
Domasio; Convergence Zone 68 Knowledge that can be accessed from the brain's neural network is not stored as an "image". Rather, the neural assemblies with their hierarchical convergence zones can provide network activity that may reenact the original explicit representation.  0
Domasio; Convergence Zone 68 Cells in high-order cortices forming the hierarchy of convergence zones are critical for the neural process of memory reenactment, but they are neither the "sole basis for" nor the "explicit site of" that neural process. There is no single basis or site for such a process. Each memory reenactment can utilize slightly different neural assemblies. 0
Domasio; Convergence Zone 70 Top steps in the hierarchy are the most distant convergence points from which divergent retroactivation can be triggered.  2
Domasio; Convergence Zone 70 There is a ceaseless production of new activity states, in early sensory cortices and in motor cortices, across time. It is these successive neural states, one after the other, that can be said to constitute "regresses" for the previous state. Neural assemblies are activated (refreshed) in a pulse-like manner by reentrant signals circulating in the network hierarchy. It is the perpetually recursive property of corticocortical systems that permits this special form of regress.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 0
Domasio; Convergence Zone 71 The reconstruction of pertinent property "representations" is accomplished in many separate cortical regions by means of long-range corticocortical feedback projections that mediate relatively synchronous excitatory activation.  1
Domasio; Convergence Zone 71 In the large scale reconstruction from higher-order cortices such as those in anterior temporal lobe, the time scale of the synchronization would be in the order of several hundred msec, and even beyond 1000 msec, the scale required for meaningful, conscious cognition.  0
Domasio; Convergence Zone 71 At more local levels, for instance, in posterior temporal cortices, the scale would be smaller, in the order of tens of milliseconds. The return projections necessary for the reconstruction are aimed toward layers I and V of the cortex. 0
Domasio; Convergence Zone 71 A convergence zone is an ensemble of neurons within which many feedforward/ feedback loops make contact.  0
Domasio; Convergence Zone 71 A convergence zone is located within a convergence region. 0
Domasio; Convergence Zone 71 There are in the order of thousands of convergence zones, which are all microscopic neuron ensembles, located within the macroscopic convergence regions that have been cytoarchitectonically defined and that number about one hundred. 0
Domasio; Convergence Zone 71 Both convergence regions and convergence zones come into existence under genetic control. 0
Domasio; Convergence Zone 71 Epigenetic control, as the organism interacts with the environment, may alter convergence regions and massively alter convergence zones through synaptic strengthening.  0
Domasio; Convergence Zone 72 A convergence zone is a means of establishing, through synaptic strengthening, preferred feedforward/feedback loops that use subsets of neurons within the ensemble. 1
Domasio; Convergence Zone 72 A subset of the neurons in the convergence zone would "learn" to activate a large number of spatially distributed neural ensembles, in temporal proximity, by means of feedback projections. 0
Domasio; Convergence Zone 72 A convergence zone develops under the influence of (1) temporally close activity in multiple feedforward and feedback lines that are simultaneously active when a number of anatomically separate regions are active and are providing the normal substrate for a given perceptual/thought process, and (2) modulatory action from feedback and feedforward projections from ipsilateral and contralateral cortices, and subcortical nuclei. 0
Domasio; Convergence Zone 72 The development of a convergence zone also depends on local interactions among neurons (e.g., from their intrinsic collateral arborizations). 0
Domasio; Convergence Zone 72 A convergence zone would be the result of convergence of feed-forward inputs, but its feedback projections operate by diverging toward the origin of feedforward projections. 0
Domasio; Convergence Zone 72 When we refer to neurons in a convergence zone we refer to the synaptic pools made up of contacts among those neurons. 0
Domasio; Convergence Zone 73 Knowledge retrieval would be based on relatively simultaneous, attended activity in many early cortical regions, intended over several recursions. 1
Domasio; Convergence Zone 73 Separate activities in early cortices would be the basis for reconstructed representations. 0
Koch and Crick; Neuronal Basis 95 To be aware of an object or an event    the brain has to construct an explicit, multilevel, symbolic interpretation of a feature of the visual scene.    By explicit we mean that a coherent neural assembly must be firing above background at that particular time    in response to the feature they symbolize. 22
Koch and Crick; Neuronal Basis 95 The term multilevel means, in psychological terms, different levels such as those that correspond, for example, to lines, eyes, or faces.    In neurological terms it means, loosely, the different levels in the visual hierarchy. 0
Koch and Crick; Neuronal Basis 95 The term 'symbolic' as applied to a neural assembly means that assembly's firing is strongly correlated with some 'feature' of the visual world and thus symbolizes it.    The meaning of such a symbol depends not only on the neuron's receptive field    but also on what other neural assemblies the neuron projects to. 0
Koch and Crick; Neuronal Basis 95 Awareness results from the firing of a coordinated subset of thalamocortical neurons that fire in some special manner for a certain length of time, probably for at least 100-200 msec.    This firing needs to activate some type of short-term memory by either strengthening certain synapses or maintaining an elevated firing rate or both. 0
Koch and Crick; Neuronal Basis 96 Movement is extracted early in the visual system as a primitive. 1
Koch and Crick; Neuronal Basis 97 Blindsight 1
Koch and Crick; Neuronal Basis 97 Active neurons in the cortical system that are apart from awareness activity at the moment can still lead to behavioral changes but without awareness. These neurons are responsible for the large class of phenomena that bypass awareness in normal subjects, such as automatic processes, priming, subliminal perception, learning without awareness, and others. 0
Koch and Crick; Neuronal Basis 97 We suspect that the majority of neurons in the cortical system at any given time are not directly associated with awareness! 0
Koch and Crick; Neuronal Basis 98 Rate coding - the simplest encoding uses mean firing frequency. 1
Koch and Crick; Neuronal Basis 99 Hypothesized that all neurons corresponding to various aspects of the object the observer is attention to fire in an oscillatory and semisynchronous manner, binding them together 1
Koch and Crick; Neuronal Basis 101 Original hypothesis was that the phase-locked firing of a set of neurons at 40 Hz was the neural correlate of visual awareness. 2
Koch and Crick; Neuronal Basis 101 Lower-layer hypothesis states that the neural correlates of visual awareness occur mainly in the lower layers 5 and 6 of the cortex. The input layer as well as neurons in the upper layers 2 and 3 are assumed to be mainly concerned with unconscious processing. 0
Koch and Crick; Neuronal Basis 101 Cognitive scientists have suggested that the content of consciousness consists of the results of neural computation while the interim results associated with the computations leading up to these results are themselves largely unconscious. 0
Koch and Crick; Neuronal Basis 102 The corticospinal pyramidal tract, with one million axons, the largest descending fiber tract from the human brain, originates in layer 5 of primary motor, supplementary motor, and premotor cortical areas and projects onto interneurons and motorneurons in the spinal cord.  1
Koch and Crick; Neuronal Basis 102 The massive projection system linking virtually the entire neocortex with the striatum originates in layer 5. 0
Koch and Crick; Neuronal Basis 102 What the cortex sends elsewhere in the brain are likely to be the results of its computations. 0
Koch and Crick; Neuronal Basis 104 Two thirds of neurons often fire in bursts of 2-4 spikes within 2-6 msec and show a small peak in the 25-50 Hz band of the power spectrum that is related to the propensity of spikes to fire in bursts. The statistical properties can be fitted by Poisson-distributed bursts with a burst-dependent refractory period. 2
Koch and Crick; Neuronal Basis 104 The remaining third of their cells have an autocorrelation function and an interspike interval distribution compatible with the notion that spikes are Poisson distributed with a refractory period. 0
Koch and Crick; Neuronal Basis 106 Pyramidal cells in both layer 5 ands layer 6 project to the various thalamic nuclei, including the lateral geniculate nucleus (LGN), as well as the inferior, lateral, and medial pulvinar nuclei. 2
Koch and Crick; Neuronal Basis 106 In primate area V1, cells in layer 5 as well as the deep part of layer 6 project to the pulvinar, while higher cortical areas project from the deep layers into the different pulvinar nuclei. 0
Koch and Crick; Neuronal Basis 106 About half of all pyramidal cells in layer 6 project back to the LGN while others project to the claustrum. This corticogeniculate projection is so massive that at least 10 times more fibers project down than project from the LGN in V1. 0
Koch and Crick; Neuronal Basis 107 An essential feature of visual processing may turn out to be the back projections to V1 (or conceivably to V1 and/or V2) as these areas are the only ones with detailed information about precise visual location.  1
Koch and Crick; Neuronal Basis 107 While inferotemporal regions do not receive a direct projection from V1, they do send backprojections to V1. 0
Koch and Crick; Neuronal Basis 107 Reentrant projections strongly emphasized by Edelman. 0
Koch and Crick; Neuronal Basis 107 Massive reentrant connections formed by the hippocampal system in the medial temporal lobe. Input comes mainly from the entorhinal cortex, and its output returns there, though to a different cortical layer. 0
Koch and Crick; Neuronal Basis 109 The brain constructs an explicit, multilevel, symbolic interpretation of parts of its environment.  [Llinás;  brain operates as a reality emulator.] 2
Koch and Crick; Neuronal Basis 109 The form of awareness associated with focal attention is caused by the firing of a temporally coordinated assembly of neurons, firing in some special manner for at least 100 or 200 msec. This special form of neuronal activity induces short-term memory. 0
Koch and Crick; Neuronal Basis 109 If neurons are not part of the transient subset of activity, they can still influence behavior but do not contribute toward awareness.  [Edelman's dynamic core] 0
Koch and Crick; Neuronal Basis 109 Underlying every direct perception is a group of neurons strongly firing and participating in the temporally coordinated neuronal assembly.  [Edelman's dynamic core] 0
Koch and Crick; Neuronal Basis 109 Semisynchronous, neuronal oscillations in the 25-55 Hz band could cause neurons to be coordinated, giving rise to short-term memory and thus to awareness.  [Edelman's dynamic core]  [Baddeley - Working Memory] 0
Koch and Crick; Neuronal Basis 109 The neural correlate of awareness occurs mainly in the lower layers. 0
Koch and Crick; Neuronal Basis 109 The neural correlate of awareness is associated with the bursting neurons in layer 5, some of which project outside the cortical system. 0
Koch and Crick; Neuronal Basis 109 The loop between deep layers in cortex, the different thalamic nuclei, and back to cortex may implement short-term memory.  [reentry]  [Edelman's dynamic core]  [Baddeley - Working Memory] 0
Koch and Crick; Neuronal Basis 109 Neurons in the upper cortical layers, are mainly concerned with unconscious processing. 0
Koch and Crick; Neuronal Basis 109 Various types of neural connections may be associated with some forms of visual awareness. Possible examples are: (1) Connections to the hippocampal system and the higher planning levels of the motor system, (2) direct back projections to V1 and possibly V2, and (3) reentrant connections within layer 4 or between cortical areas at the same level in the anatomical hierarchy.
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Llinás; Perception as Oneiric-like 113 Wakefulness is a dreamlike state modulated by specific sensory inputs.  4
Llinás; Perception as Oneiric-like 113 Thalamus is regarded as the functional and morphological gate to the forebrain. With the exception of the olfactory system, all sensory messages reach the cerebral cortex through the thalamus. 0
Llinás; Perception as Oneiric-like 113 Connectivity between the thalamus and the cortex is bidirectional. Layer 6 pyramidal cells project back to the area of the thalamus where their specific input arises, and layer 5 cells project to the nonspecific thalamus.  0
Llinás; Perception as Oneiric-like 113 The number of corticothalamic fibers is about one order of magnitude larger than the number of thalamocortical axons. 0
Llinás; Perception as Oneiric-like 113 The number of optic nerve axons projecting to the LGN is much smaller than the number of corticothalamic axons projecting to the LGN. 0
Llinás; Perception as Oneiric-like 113 Sensory input from the thalamus is necessary for perception; however, the specific thalamocortical input accounts for a minority of the synaptic contacts in the cortex. 0
Llinás; Perception as Oneiric-like 114 Electrophysiological studies indicate that the intrinsic membrane properties of neurons allow them to oscillate or resonate at different frequencies. This intrinsic neuronal support of rhythmic oscillatory activity may play a fundamental role in CNS function. 1
Llinás; Perception as Oneiric-like 114 The brain is essentially a closed system capable of self-generated oscillatory activity that determines the functionality of events specified by the sensory stimuli. 0
Llinás; Perception as Oneiric-like 114 Only a minor part of thalamocortical connectivity is devoted to the reception and transfer of sensory input.  0
Llinás; Perception as Oneiric-like 114 The number of cortical fibers projecting to the specific thalamic nuclei is much larger than the number of fibers conveying the sensory information to the thalamus. 0
Llinás; Perception as Oneiric-like 114 A large part of the thalamocortical connectivity is organized in what is presently known as reentrant activity (Edelman) or previously viewed as reverberating activity. 0
Llinás; Perception as Oneiric-like 114 Neurons with intrinsic oscillatory capabilities in the complex synaptic network allow the brain to generate dynamic oscillatory states, which can shape the computational events evoked by sensory stimuli. 0
Llinás; Perception as Oneiric-like 114 Functional states such as wakefulness (or REM sleep and other sleep stages) appear to be particular examples of the multiple variations provided by the self-generated brain activity. 0
Llinás; Perception as Oneiric-like 115 The localization of function in the brain began with the identification of a cortical speech center by Broca and was followed by the discovery of point-to-point somatotopic maps in the motor and sensory cortices (Penfield and Rasmussen 1950), and in the thalamus (Mountcastle and Hennemann 1949, 1952). 1
Llinás; Perception as Oneiric-like 115 A totally different type of functional geometry (Pellionisz and Llinas 1982) suggests the existence of temporal mapping. This has been far more difficult to conceptualize, since its study requires an understanding of simultaneity in brain function not usually considered in neuroscience. 0
Llinás; Perception as Oneiric-like 115 Magnetoencephalographic recordings performed in awake humans revealed the presence of continuous and coherent 40-Hz oscillations over the entire cortical mantle. 0
Llinás; Perception as Oneiric-like 115 Phase comparison of the oscillatory activity recorded from different cortical regions revealed the presence of a 12- to 13-msec phase shift between the rostral and caudal pole of the brain. 0
Llinás; Perception as Oneiric-like 118 Magnetoencephalography (MEG) was used in three sets of studies concerning: (1) the presence of 40 Hz activity during sleep, (2) the possible differences between 40 Hz resetting in different sleep/wakefulness states, (3) the question of 40 Hz during REM sleep. 3
Llinás; Perception as Oneiric-like 118 In the MEG studies, spontaneous magnetic activity was continuously recorded and filtered at 35-45 Hz during wakefulness, delta sleep, and REM sleep, using a 37-channel sensor array. 0
Llinás; Perception as Oneiric-like 118 Fourier analysis of the spontaneous, broadly filtered rhythmicity (1-200 Hz) demonstrated a large peak of activity at 40-Hz over much of the cortex. 0
Llinás; Perception as Oneiric-like 119 During wakefulness and REM sleep, a very specific 40-Hz thalamocortical resonance is active and has very similar global properties.  1
Llinás; Perception as Oneiric-like 120 Front-to-back phase shift of the 40-Hz activity over the head during REM sleep; well-organized 12-msec phase shift for the 40-Hz oscillation;  1
Llinás; Perception as Oneiric-like 120 Overall speed of the rostrocaudal scan, which averaged approximately 12.5 msec, corresponded quite closely to half a 40-Hz period. This number is the same as that calculated for a quantum of consciousness in psychophysical studies in the auditory system. 0
Mumford; Neuronal Architectures 135 In the cortex, roughly 65% of all cells are pyramidal cells that send their output to distant cortical areas, as well as locally via their axon collaterals. 15
Mumford; Neuronal Architectures 135 Pattern theory says that tightly coupled cortical areas seek, via some kind of relaxation functionality, to arrive at a mutual agreement in which lower areas' specific data form a fit with known, more abstract categorizations stored in higher areas' memory of prior activity. 0
Mumford; Neuronal Architectures 135 Bottom-up assertions of facts have to be included along with top-down memories of expected patterns. 0
Mumford; Neuronal Architectures 136 Correlated spikes from full spike trains may be more meaningful than responses from individual neurons.  1
Mumford; Neuronal Architectures 136 Set of spikes may be much less stochastic,    carrying information transmitted between areas,    and correlated much more precisely and predictably    with identifiable aspects of an input.  0
Posner; Constructing Neuronal Theories 188 Anterior cingulate gyrus has strong connections with a variety of other neural areas and plays a critical role in attention and what is meant by consciousness, and relates both to awareness and to voluntary control. 52
Posner; Constructing Neuronal Theories 189 Subjective experience is related to activation of the anterior cingulate attention system. 1
Posner; Constructing Neuronal Theories 189 Degree of activation of the anterior cortex attention system increases with the number of targets presented in a semantic monitoring task and decreases with the amount of practice in the task. 0
Posner; Constructing Neuronal Theories 189 Anterior cortex attention system is active during tasks requiring the detection of visual stimuli, when the targets involve color, form, motion, or words semantics. 0
Posner; Constructing Neuronal Theories 189 Anterior attention system is activated when listening passively to words,    but not when watching these words. 0
Posner; Constructing Neuronal Theories 189 Intrusive nature of auditory words to consciousness    when they are presented in a quiet background.     Auditory words seem to capture awareness.     Reading does not have this intrusive character. 0
Posner; Constructing Neuronal Theories 190 Anterior cortex attention system    is more active during conflict blocks    than during non-conflict blocks.  Conflict between word  name and ink color produces a strong conscious effort to inhibit saying the written word. 1
Posner; Constructing Neuronal Theories 190 Relation between vigilance system and awareness.   0
Posner; Constructing Neuronal Theories 190 When a person attends to a source of sensory input    in order to detect an infrequent target,    the subjective feeling is up emptying the head    of thoughts or feelings. 0
Posner; Constructing Neuronal Theories 190 Subjective "clearing of consciousness" appears to be accompanied by    an increase in activation of the right frontal lobe vigilance network    and a reduction in the anterior cingulate. 0
Posner; Constructing Neuronal Theories 190 Feelings of effort associated with target detection or inhibiting prepotent responses    are accompanied by evidence of cingulate activation. 0
Posner; Constructing Neuronal Theories 190 Clearing of thought is accompanied by evidence of cingulate inhibition. 0
Posner; Constructing Neuronal Theories 190 PET studies have revealed important anatomical aspects of word reading. 0
Posner; Constructing Neuronal Theories 190 The right posterior temporal parietal area, activated both by both consonants strings and words, is thought to be a visual representation that is prelexical. 0
Posner; Constructing Neuronal Theories 190 The left ventral occipital area is involved in "visual word form," a representation of the orthography of the letter string in which the individual letters are combined into a single chunk. 0
Posner; Constructing Neuronal Theories 191 PET studies imply that letter strings are represented within the visual system    both as unorganized features or letters    and within a unified visual word form. 1
Posner; Constructing Neuronal Theories 191 When people attend to    color, motion, or form,    appropriate posterior prestriate areas are increased in activation. 0
Posner; Constructing Neuronal Theories 191 Attention appears to amplify the activity of anatomical areas in which the related computations occur. 0
Posner; Constructing Neuronal Theories 191 Studies show a very strong posterior tempoparietal asymmetry    in which electrical activity at about 100 ms    is larger from the right hemisphere    than from the left. 0
Posner; Constructing Neuronal Theories 191 Study results fit the idea of the right posterior generator    related to visual features    occurring within the first 100 ms. 0
Posner; Constructing Neuronal Theories 191 Study results suggest that when attending to features, people search a representation located in the right posterior temporal lobe. 0
Posner; Constructing Neuronal Theories 192 PET studies show that the left frontal area is active when subjects deal with the meaning of a word. 1
Posner; Constructing Neuronal Theories 192 When the task requires association of several words to a given input,    the left frontal area is joined by activation in Wernicke's area. 0
Posner; Constructing Neuronal Theories 192 If attention serves to amplify computations,    it should be possible to see amplified waveforms    in the right posterior area in feature analysis    and in the left frontal area and semantics. 0
Posner; Constructing Neuronal Theories 192 Research results show that the left frontal area was more active at about 200-300 ms when the task was semantic,    while the right posterior area was more active when the task was feature search. 0
Posner; Constructing Neuronal Theories of Mind 193 Reentrant signaling establishes correlations between cortical maps,    within or between different levels of the nervous system. 1
Posner; Constructing Neuronal Theories of Mind 193 Visual computation occurs at 100 ms,    followed by semantic computation, which might be complete by 200-300 ms. 0
Posner; Constructing Neuronal Theories of Mind 193 The area making a semantic computation was amplified in electrical activity of about 100 ms after the initial computation. 0
Posner; Constructing Neuronal Theories of Mind 194 Attention    amplifies computations    within particular areas,    but does so by reentering the area,    not by amplifying its initial activation. 1
Posner; Constructing Neuronal Theories of Mind 195 Anterior cingulate connections    to limbic,    thalamic,    and basal ganglia pathways    distributes frontal network activity    to the widely dispersed connections involved in cognitive computations. 1
Posner; Constructing Neuronal Theories of Mind 195 The posterior attention network (including the parietal lobe and associated thalamic and midbrain areas)    and the anterior attention network (including the anterior cingulate)    influence each other   via direct cortical projections,    but also indirectly through a comparator operation involving the basal ganglia. 0
Posner; Constructing Neuronal Theories of Mind 195 A sensory event facilitates processing at a location due to activation of the posterior network,    but an expectation also operates via the anterior network to facilitate the expected location. 0
Posner; Constructing Neuronal Theories of Mind 195 In the basal ganglia loops,    a direct pathway between the anterior cingulate and striatum serves as a reverberating circuit    to maintain expected locations and amplify them when their locations match. 0
Posner; Constructing Neuronal Theories of Mind 197 The distributed connections by which the attention systems    assume control over various functions    may develop over a considerable period of life. 2
Posner; Constructing Neuronal Theories of Mind 197 Elementary mental operations    are localized    in discrete neural areas. 0
Posner; Constructing Neuronal Theories of Mind 198 Cognitive tasks    are performed by a network    of widely distributed neural systems. 1
Posner; Constructing Neuronal Theories of Mind 198 Computations in a network    interact by means of "reentrant" processes. 0
Posner; Constructing Neuronal Theories of Mind 198 Orderings of computations is necessary for performance.    Ordering does not take place by a strict serial organization.    Instead, computations pass information back and forth    to coordinate their results. 0
Posner; Constructing Neuronal Theories of Mind 198 Precise connections exist    between anatomically distant areas.    A particular anatomical area is active whenever its computation is required.    Since computations are often contingent on information from another area,    information is fed back to reenter the critical areas. 0
Posner; Constructing Neuronal Theories of Mind 198 Hierarchical control is a property of network operation. Discovery of a separate network of anatomical areas devoted to attention provides a basis for establishing executive control over widely distributed networks. 0
Posner; Constructing Neuronal Theories of Mind 198 Research results support the idea of executive control by attention systems. 0
Posner; Constructing Neuronal Theories of Mind 198 Activation of a computation    produces a temporary reduction in the threshold for its reactivation.    This principle underlies the cognitive phenomenon of priming. 0
Posner; Constructing Neuronal Theories of Mind 198 For the processing of words,    priming exists at the level of attributes,    word forms,    phonology,    and semantics. 0
Posner; Constructing Neuronal Theories of Mind 198 When a computation is repeated,    it's reduced threshold is accompanied by reduced effort and less attention. 0
Posner; Constructing Neuronal Theories of Mind 199 Activating a computation    from sensory input (bottom-up)    and from attention (top-down)    involves many of the same neurons. 1
Posner; Constructing Neuronal Theories of Mind 199 Practice in the performance of any computation    will decrease the neural networks    necessary to perform it. 0
Singer; Temporal Correlations in Neocortical Processing 201 Putative Functions of Temporal Correlations in Neocortical Processing 2
Singer; Temporal Correlations in Neocortical Processing 201 Cells have been found those responses distinguish between    familiar and unfamiliar objects,    are selective for particular aspects of faces,    reflect precisely the location of a remembered target,    or predict with accuracy the direction of an eye movement. 0
Singer; Temporal Correlations in Neocortical Processing 201 A particular neuronal state would have to take into account not only the rate and specificity of individual neuron responses    but also the relations between discharges of distributed neurons. 0
Singer; Temporal Correlations in Neocortical Processing 204 Cells occupying higher levels in the processing hierarchy tend to be selective for more complex constellations of features than cells at lower levels. 3
Singer; Temporal Correlations in Neocortical Processing 205 Representations    consist of assemblies of a large number of simultaneously active neurons    that may be contained both in a single cortical area and also distributed over many cortical areas. 1
Singer; Temporal Correlations in Neocortical Processing 205 The essential feature of assembly coding    is that individual cells    can participate at different times    in the representation of different objects. 0
Singer; Temporal Correlations in Neocortical Processing 207 The formation of coherently active assemblies can serve to enhance the saliency of responses    to features that can be associated in a "meaningful" way. 2
Singer; Temporal Correlations in Neocortical Processing 207 The concept of "binding by synchrony" has been applied to intermodal integration and even to high-level processes underlying phenomena such as attention and consciousness. 0
Singer; Temporal Correlations in Neocortical Processing 212 The hypothesis of temporally coded assemblies requires that the probabilities with which distributed cells    synchronize their responses should reflect some of the Gestalt criteria applied in perceptual grouping. 5
Singer; Temporal Correlations in Neocortical Processing 212 Synchronization probability within a particular cortical area    decreases with increasing distance between the cells.    If the cells are so closely spaced that their receptive fields overlap,    the probability is high that their responses will exhibit synchronous epochs    if invoked with a single stimulus. 0
Singer; Temporal Correlations in Neocortical Processing 217 Because response synchronization occurred often in association with oscillatory activity in the range of 30-60 Hz, it has been proposed that the observed synchronization phenomena in the visual cortex are due to common oscillatory input from subcortical centers. 5
Singer; Temporal Correlations in Neocortical Processing 217 Oscillatory activity in the 30-60 Hz range has been described both for retinal ganglion cells and thalamic neurons. 0
Singer; Temporal Correlations in Neocortical Processing 218 Thalamic oscillations    are backpropagated from cortex    by the corticothalamic projections. 1
Singer; Temporal Correlations in Neocortical Processing 218 Large-scale synchronization of distributed thalamic neurons is common during sleep spindles,    but correlated 30-60 Hz oscillatory activity has been observed only between closely spaced cells. 0
Singer; Temporal Correlations in Neocortical Processing 219 In mammals, corticocortical connections develop mainly postnatally    and attain their final specificity through an activity-dependent selection process. 1
Singer; Temporal Correlations in Neocortical Processing 227 There is ample evidence from brain structures other than the visual cortex that groups of cells engage in synchronous rhythmic activity in the gamma frequency range. 8
Singer; Temporal Correlations in Neocortical Processing 227 The fact that gamma activity occurs in the awake brain    and increases with attention and preparation of motor acts    suggests that it is functionally relevant. 0
Stevens; Cortical Theory 239 What Form should a Cortical Theory take? 12
Stevens; Cortical Theory 239 Many functionally distinct cortical regions, over 30 in the visual system. 0
Stevens; Cortical Theory 240 Functionally distinct cortical regions, like V1 and MT, might perform identical mathematical operations on different sorts of inputs.  [Bayesian inference]   1
Stevens; Cortical Theory 240 Activity-dependent rewiring of cortical circuits could modify the computations performed by even initially uniform cortices. The character of some mathematical operation might vary continuously across even an apparently uniform cortical region like the primary visual cortex.  [Bayesian inference]   0
Stevens; Cortical Theory 240 How many inputs and outputs are present in cortex?    The answer depends on how many types of neurons are present.     Estimates indicate that the number of Input and output neuron types should not a large number, perhaps 10 to 100. 0
Stevens; Cortical Theory 240 Synaptic transmission is a stochastic process. Neurotransmitter is released at axon terminals in packets—called quanta—so that the total effect of a nerve impulse arrival is an integral multiple of the smallest effect, the one produced by a single quantum. The quanta are released probabilistically according to a Poisson process. 0
Stevens; Cortical Theory 241 Probability of release of a packet quantum at an individual synapse is generally very low, about 0.1 to 0.5. 1
Stevens; Cortical Theory 241 Any particular neuron generally seems to receive only one or two synapses from any other neuron.  0
Stevens; Cortical Theory 241 In hippocampus, it has been estimated that a given axon usually makes only a single synapse (average estimated to be 1.3) on its target cell. 0
Stevens; Cortical Theory 241 Lateral geniculate axons that project to visual cortex make only one or a few (up to about eight) synapses on their targets. 0
Stevens; Cortical Theory 241 When a pair of cells is connected, the communication link between them is quite unreliable for pulse arrival, although it is predictable in a statistical sense.  0
Stevens; Cortical Theory 241 The effect of one neuron on another is generally small and uncertain. 0
Stevens; Cortical Theory 241 A single input has only a relatively small effect on its target. 0
Stevens; Cortical Theory 241 The random nature of synaptic transmission makes neuronal behavior uncertain; networks of neurons must be described probabilistically.  0
Stevens; Cortical Theory 242 Probabilistic descriptions are not required for all neurons in the brain. For Purkinje cells in the cerebellum, for example, in which one neuron makes thousands of synapses on its target cell, statistical fluctuations in synaptic strength are very small. 1
Stevens; Cortical Theory 242 A cubic millimeter of cortex—a good candidate for the size of a computational unit — contains 105 neurons, 109 synapses. 0
Stevens; Cortical Theory 242 Each neuron receives about 104 synapses and communicates with about 104 other neurons. 0
Stevens; Cortical Theory 242 Most neuronal connections are intracortical. 0
Stevens; Cortical Theory 242 Because single neurons have small and uncertain effects on other neurons, the cortical description must be carried out in terms of neuronal populations rather than at the level of individual cells. 0
Stevens; Cortical Theory 242 Layer 4 neurons have a dendritic tree with a diameter of about 0.3 mm. 0
Stevens; Cortical Theory 242 Layer 4 is about 0.3 mm thick, and cortex has a density of about 105 neurons per mm3. 0
Stevens; Cortical Theory 242 All of the neurons in layer 4 that fall within a cylinder having a radius of about 0.3 mm will have overlapping dendritic trees. The number of neurons that overlap is estimated to be approximately 8000. A significant fraction of this population of neurons should represent essentially the same information. 0
Stevens; Cortical Theory 242 A given axon generally arborizes over a considerable region of cortex with an arbor diameter of perhaps 0.5 mm, and forms about 2000 boutons, each of which makes one or two synapses. 0
Stevens; Cortical Theory 243 Neurons of the same functional class and in the same cortical layer share nearly the same potential synaptic inputs whenever their cell bodies are separated by several hundred microns or less, and the degree of similarity in their inputs increases as the distance between cell bodies decreases.  1
Stevens; Cortical Theory 243 The overall stochastic nature of neuronal behavior suggests that the physiologically meaningful signal from cortex should be the average firing rates of a population of perhaps 100 to 1000 neurons near a particular cortical site. 0
Stevens; Cortical Theory 243 The behavior of cortex at a particular point is described by the firing in a population of neurons. The total firing that represents this population would be determined by a weighted average of the appropriate neurons in the cortical region that surrounded the point, perhaps with weights that are described by a spatial Gaussian. Moving from one cortical location to an adjacent one, the variables describing cortical state would vary continuously with cortical position. 0
Stevens; Cortical Theory 243 A theory of cortex must be coarse-grained and treat cortical inputs and outputs as continuous variables that represent the summed behavior of appropriately sized and selected neuron populations. 0
Stevens; Cortical Theory 243 The prominent recurrent nature of lateral intracortical connections and relatively wide spatial distribution of cortical inputs mean that the cortical output at any one location must depend on both the input and output over relatively great expanses of cortex. That is, the output at any one point must be a functional, of both inputs and outputs. 0
Ullman; Sequence Seeking Counterstreams 257 Sequence Seeking Counterstreams 14
Ullman; Sequence Seeking Counterstreams 257 It would take an expert to distinguish rat frontal cortex from sheep parietal cortex, or cat auditory cortex from monkey somatosensory cortex. 0
Ullman; Sequence Seeking Counterstreams 257 In visual recognition, the task involves establishing a connection between an incoming pattern and stored object representations in visual memory.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 0
Ullman; Sequence Seeking Counterstreams 257 Visual input is processed through a sequence of stages that includes edge detection, feature extraction of varying complexity, and normalization for size, position, and orientation. The resulting neural representation is then compared with memory objects.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 0
Ullman; Sequence Seeking Counterstreams 258 An attractive model for mental object search and matching is to apply bidirectional methods, using both bottom-up and top-down processing. This counterstreams notion fits well with the 1-to-6 layered architecture of the cortex.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 1
Ullman; Sequence Seeking Counterstreams 264 Planning motor actions can be implemented in terms of a sequence of movement trajectories based on a stored repertoire of elementary movements. (FAPs) These basic movements can then be transformed and concatenated together to generate more complex movements.  [Stereotyped motor programs]  [FAPs] 6
Ullman; Sequence Seeking Counterstreams 264 The sequence-seeking model requires two streams going in opposite directions with the appropriate cross-connections. The counterstreams go up and down between layers 1 and 6 of the cortex, with lateral cross connections between nearby areas.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 0
Ullman; Sequence Seeking Counterstreams 264 The ascending stream goes through layer 4 to a subpopulation of the superficial layers, and then projects to layer 4 of the next cortical area. 0
Ullman; Sequence Seeking Counterstreams 264 The descending stream goes through a different subpopulation of the superficial layers to a descending subpopulation of the infragranular layers (often in layer 6), and from there to descending superficial layers of a preceding area. 0
Ullman; Sequence Seeking Counterstreams 265 Layer 5 (or parts of it) may be involved in control functions.  1
Ullman; Sequence Seeking Counterstreams 265 Layer 5's orderly connections to subcortical structures (e.g., from visual cortex to the pulvinar and the superior colliculus, structures implicated in controlling attention and eye movements) that are reciprocally connected in a topographic manner to multiple visual areas. 0
Ullman; Sequence Seeking Counterstreams 265 Firing pattern of a population of pyramidal cells in Layer 5 can initiate synchronized rhythms and project them on neurons in all layers. 0
Ullman; Sequence Seeking Counterstreams 265 A separation between the ascending and descending populations is evident in the connections involving layer 4: the ascending streams terminate in layer 4, the descending streams always avoid it. In the superficial layers the situation is more difficult to assess. 0
Ullman; Sequence Seeking Counterstreams 267 In the magnocellular projection from V1 to V2, the forward projection originated mainly in 4B, while the back projection in mainly other layers (2b).  2
Ullman; Sequence Seeking Counterstreams 268 Connections between cortical areas can be classified as forward, backward, or lateral connections on the basis of the laminar distribution of their source and destination. Lateral connections terminate in all layers. 1
Ullman; Sequence Seeking Counterstreams 270 Counterstreams sequence-seeking model is a bidirectional search performed by top-down and bottom-up streams seeking to meet. 2
Ullman; Sequence Seeking Counterstreams 270 The counterstreams functional architecture accounts for several basic features of cortical circuitry: the predominantly reciprocal connectivity between cortical areas; the forward, backward, and lateral connection types; the regularities in the distribution patterns of interarea connections; the organization in 5-6 main layers; the effects of back projections. 0
Van Essen; Dynamic Routing Strategies 271 Dynamic Routing Strategies 1
Van Essen; Dynamic Routing Strategies 272 Ability to recognize a wide range of highly complex patterns (e.g. faces) is relegated to a small number of modules situated at high levels of the visual hierarchy in inferotemporal cortex. 1
Van Essen; Dynamic Routing Strategies 272 Visual attention is a mechanism for dynamically regulating information flow so as to bring information from the visual field into an appropriate format for the high-level object recognition center. 0
Van Essen; Dynamic Routing Strategies 272 Attention can be directed to different locations and to different spatial scales. 0
Van Essen; Dynamic Routing Strategies 272 Attention shifts can be initiated by bottom-up cues and/or top-down influences. 0
Van Essen; Dynamic Routing Strategies 272 When initiated by bottom-up cues, attentional shifts occur with a finite temporal delay (50-100 ms) and tend to persist in any given location for a relatively brief period.  In this respect, they are analogous to saccadic eye movements, except they occur on a faster time scale. 0
Van Essen; Dynamic Routing Strategies 273 Attention is directed not simply to the initial cue, but to whatever image data lie within the window of attention once it has been shifted. 1
Van Essen; Dynamic Routing Strategies 273 Visual attention acts as an informational bottleneck that reduces to manageable levels the amount of image data reaching high-level cortical centers involved in pattern recognition. 0
Van Essen; Dynamic Routing Strategies 273 For complex patterns to be recognized, it is important that information about spatial relationships be preserved within the window of attention. 0
Van Essen; Dynamic Routing Strategies 274 Motor system is capable of selecting among a large repertoire of stereotyped motor routines.  [Stereotyped motor programs]  [FAPs] 1
Van Essen; Dynamic Routing Strategies 274 Bottom-up sensory cues as well as the top-down cognitive control. 0
Van Essen; Dynamic Routing Strategies 275 Neurobiologically plausible mechanism for shifting and rescaling the representation of an object from the retinal reference frame into an object-centered reference frame. 1
Van Essen; Dynamic Routing Strategies 275 Information in the retinal reference frame is represented on a neural map (for instance, the topographic representation in V1). 0
Van Essen; Dynamic Routing Strategies 275 Hypothesize that information in the object-centered reference frame is also represented on a neural map that preserves some degree of information about local spatial relationships.  0
Van Essen; Dynamic Routing Strategies 275 Each sample node in the high level map may be thought of as a feature vector representing various local image properties (such as orientation, texture, and depth). 0
Van Essen; Dynamic Routing Strategies 276 Efficacy of transmission of cortical pathways is modulated by the activity of control neurons whose primary functionality is to dynamically route information through successive stages of the cortical hierarchy. 1
Van Essen; Dynamic Routing Strategies 278 Purpose of attention is to focus the neural resources for recognition on a specific region within a scene. 2
Van Essen; Dynamic Routing Strategies 278 Salient areas of a scene can often be defined on the basis of relatively low-level cues such as pop-out due to motion, depth, texture, or color. 0
Van Essen; Dynamic Routing Strategies 284 Major visual processing pathways of the primate brain. Information from the retinogeniculostriate pathway enters the visual cortex through area V1 in the occipital lobe and proceeds through a hierarchy of visual areas that can be subdivided into two major functional streams. 6
Van Essen; Dynamic Routing Strategies 284 The "form" pathway leads ventrally through V4 and inferotemporal cortex (IT) and is mainly concerned with object identification, regardless of position or size. 0
Van Essen; Dynamic Routing Strategies 285 The "where" pathway leads dorsally into the posterior parietal complex, and is concerned with the locations and spatial relationships among objects, regardless of their identity.  1
Van Essen; Dynamic Routing Strategies 285 Pulvinar, a subcortical nucleus of the thalamus, makes reciprocal connections with all of the visual processing cortical areas. 0
Van Essen; Dynamic Routing Strategies 285 V1 has about twice the density of neurons per unit surface area as the rest of neocortex. 0
Van Essen; Dynamic Routing Strategies 285 Model of attentional processing in visual cortex. Different stages of the network correspond to the major cortical areas in the "form" pathway. Two stages for V1: V1a corresponding to layer 4C, and V1b corresponding to superficial layers. Remaining areas—V2, V4, and inferotemporal cortex (IT)— occupy one stage apiece.  0
Van Essen; Dynamic Routing Strategies 285 Each node of the attentional processing model corresponds to a feature vector that represents the activity profile of a large group (hundreds or thousands) of neurons in each visual area.  0
Van Essen; Dynamic Routing Strategies 287 Neural resources in IT are probably devoted to recognition rather than representing the contents of the window of attention itself. 2
Van Essen; Dynamic Routing Strategies 287 Hypothesize that the pulvinar plays an important role in providing the control signals required for the routing circuit of attentional control. 0
Van Essen; Dynamic Routing Strategies 287 Pulvinar is reciprocally connected to all areas in the form pathway, making it a plausible candidate for modulating information flow from V1 to IT. 0
Van Essen; Dynamic Routing Strategies 287 Pulvinar receives projections    from both posterior parietal cortex and superior colliculus,    which are known to encode the direction of saccade targets    and may also be involved in setting up attentional targets. 0
Van Essen; Dynamic Routing Strategies 287 Neurophysiological studies, lesion studies, and neuroimaging studies of the pulvinar, suggest that it plays an important role in visual attention. 0
Van Essen; Dynamic Routing Strategies 287 Pulvinar is spatially localized while at the same time able to communicate with vast areas    of the visual cortex.  0
Van Essen; Dynamic Routing Strategies 287 Relative proximity of pulvinar neurons to each other could facilitate the competitive and cooperative interactions among the control neurons that are necessary to enforce the constraint of having a single window of attention. 0
Van Essen; Dynamic Routing Strategies 287 Intrapulvinar communication could possibly be subserved by interneurons within the pulvinar or through the reticular nucleus of the thalamus. 0
Van Essen; Dynamic Routing Strategies 288 Neural gating mechanisms are believed to play an important role in many aspects of nervous system function. 1
Van Essen; Dynamic Routing Strategies 288 A pyramidal neuron    may branch to several cortical areas    and make synaptic connections to a multitude of neurons. 0
Van Essen; Dynamic Routing Strategies 289 Dynamic routing model    predicts that the receptive field of cortical neurons    should change their position or size    as attention is shifted or rescaled. 1
Van Essen; Dynamic Routing Strategies 293 Synchrony of neural firing could serve as a code for linking features common to a given object. 4
Van Essen; Dynamic Routing Strategies 293 Temporal information    might be used to solve the "binding problem" and thereby mediate aspects of figure/ground segregation,    attention,    and perhaps even consciousness. 0
Van Essen; Dynamic Routing Strategies 294 Ullman has proposed that pattern recognition is achieved by an "counterstreams" strategy,    in which information about stored patterns flows top-down    at the same time that information about currently viewed patterns flows in the bottom-up direction.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 1
Van Essen; Dynamic Routing Strategies 294 Ullman's counterstreams strategy    involves multiple coexisting representations    that flow in each direction,    and recognition is manifested by a winner-take-all computation    to find the best match    between patterns propagating in the two directions.  [recursion]  [Bayesian inference]  [Fuster's  perception-action cycle] 0
Van Essen; Dynamic Routing Strategies 296 Brain's motor system includes cerebellum as well as cerebral cortical areas and numerous subcortical nuclei in the forebrain (basal ganglia), thalamus, midbrain, and brainstem. 2
Van Essen; Dynamic Routing Strategies 296 Each neuron "votes" for a particular direction of movement that it influences,    and the strength of its vote is proportional to its firing rate.  0
Van Essen; Dynamic Routing Strategies 297 To have a particular digit or other appendage    execute movement,    the stereotyped spatiotemporal pattern    would be selectively routed into the neural populations in motor cortex that control the relevant digits.  [Stereotyped motor programs]  [FAPs] 1
Van Essen; Dynamic Routing Strategies 297 Representation of each digit or other appendage    is likely to be an overlapping and interleaved    ensembles of neurons. 0
Van Essen; Dynamic Routing Strategies 297 Information about a motor routine    might be communicated indirectly    between cortical areas via the well-known route involving the basal ganglia and thalamus,    rather than via direct corticocortical connections. 0
Van Essen; Dynamic Routing Strategies 297 Thalamic motor nuclei (VA and the VL)    terminate mainly in the middle layers of motor cortex. 0
Van Essen; Dynamic Routing Strategies 299 Multiplicative operations    whereby "control neurons"    dynamically modulate the connection    between two other groups of neurons. 2
Van Essen; Dynamic Routing Strategies 299 Complex nonlinearities have been introduced to achieve flexibility in neural computational systems using dynamic links or oscillations. 0
Van Essen; Dynamic Routing Strategies 299 Distinguish control functions from information flow and processing. 0
Van Essen; Dynamic Routing Strategies 299 Three-way interactions provide a contextual framework for modifying the interpretation of information, which is an essential ingredient for cognitive processing. 0
Van Essen; Dynamic Routing Strategies 299 Hierarchical interpretative systems 0
Van Essen; Dynamic Routing Strategies 299 Complex circuits requires physical structure to be largely laid down by genetic factors. 0
Van Essen; Dynamic Routing Strategies 299 Well-defined structure for the neocortex and its connections to subcortical bodies that is replicated across individuals and not modified on a gross scale by experience. 0
Van Essen; Dynamic Routing Strategies 299 Whereas the details on the information about complex objects contained within the inferotemporal cortex differs between individuals, the strategies for acquiring that information, and the way it is stored and retrieved, is presumed to be very similar. 0