Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Functional Modularity of Cortex

Functional Modularity Of Cortex

Specialized functional areas of the cortex such as sensory area of visual cortex, somatosensory cortex, motor cortex, premotor cortex, ‘what’ and ‘where’ pathways of association cortex, Broka and Wernicke language areas, and working memory of prefrontal cortex.

Modular areas of the cortex were identified a century ago with the Brodmann areas.

Pyramidal neurons are the principal neuron in all three basic types of cortex: olfactory, hippocampal, and neocortex. (Shepherd; Synaptic Organization of the Brain, 25)

The radial unit hypothesis posits that the output of proliferative units (at the ventricle) is translated by glial guides to the expanded cortex in the form of ontogenetic columns. (Neocortex Outer Region Subventricular Zone Development)

Inferior frontal regions are known from lesion studies to be involved in social awareness and the ability to possess a value system and experience guilt; lesions in this region tend to produce uncensored and potentially antisocial behavior. (Andreasen; Creating Brain, 74)

Binding problem  (Koch; Quest for Consciousness, 167)

Neocortex is a layered, sheet-like structure  (Koch; Quest for Consciousness, 71)

Columnar organization of the Cortex (Quest 28, 81)  (Calvin; Neil’s Brain, 94)

Prefrontal cortex  (Koch; Quest for Consciousness, 129)

Functionally Distinct Cortical Regions

Nervous system appears very much to be organized in functional modules. (Llinás; I of the Vortex, 152)

Schematic diagram showing the brain common to all vertebrates including humans. (Changeux; Neuronal Man, 44)

Cortex is an interconnected six-layer sheet of about ten billion neurons with about a million billion connections. (Edelman; Bright Air, 104)

Cortex is arranged in functionally segregated maps that are reentrantly connected that subserve all the different sensory modalities and motor responses. (Edelman; Bright Air, 104)

Spatial Localization of Function

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). (Koch, Neuronal Theories;

Llinás; Perception as Oneiric-like, 115)

Many functionally distinct cortical regions, over 30 in the visual system. (Koch, Neuronal Theories; Stevens; Cortical Theory, 239)

Functionally distinct cortical regions, like V1 and MT, might perform identical mathematical operations on different sorts of inputs. (Koch, Neuronal Theories; Stevens; Cortical Theory, 240)

Temporal Mapping of Functionality

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. (Llinás; Perception as Oneiric-like, 115)

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. (Koch, Neuronal Theories; Stevens; Cortical Theory, 240)

 

Sensory Cortex

Right somatosensory cortices -- insula, S2, and S1 regions of the right cerebral hemisphere. This is the set of regions in which the brain accomplishes the highest level of integrated mapping of body state. (Damasio; Looking for Spinoza, 117)

Right somatosensory cortices are dominant with regard to integrated body mapping. (Damasio; Looking for Spinoza, 117)

Right somatosensory cortices have been consistently associated with defects in emotion and feelings, such as anosognosia and neglect, whose basis is a defective idea of the current body state. (Damasio; Looking for Spinoza, 117)

Right versus left asymetery in the function of the human somatosensory cortices probably is due to a committed participation of the left somatosensory cortices in language and speech. (Damasio; Looking for Spinoza, 117)

Somatosensory cortex ("sensory homunculus"), motor cortex ("motor homunculus"), Wilder Penfield maps. - (illustration) (Llinás; I of the Vortex, 205)

Functional modularity of visual processing pathways

The major visual processing pathways of the primate brain are the "form" pathway through the inferotemporal cortex (IT) and the "where" pathway, which leads dorsally into the posterior parietal complex.  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.  The "form" pathway leads ventrally through V4 and the inferotemporal cortex (IT) and is mainly concerned with object identification, regardless of position or size.  The "where" pathway leads dorsally to the posterior parietal complex, and is concerned with the locations and spatial relationships among objects, regardless of their identity. The pulvinar, a subcortical nucleus of the thalamus, makes reciprocal connections with all of these cortical areas.  (Koch, Neuronal Theories; Van Essen; Dynamic Routing Strategies, 284)

At least twenty distinct visual areas have been identified, plus about seven more that are partly visual. (Crick; Astonishing Hypothesis, 149)

Early visual cortices (V1, V2, V3, V4, V5) - (diagram) (Damasio; Descartes’ Error, 91)

Topographic areas of visual cortex, V2, V3, V3A, V4  (Koch; Quest for Consciousness, 134)

Color perception   (Koch; Quest for Consciousness, 137)

Association Cortex

Visual association cortices, especially the right visual cortices of the ventral occipito-temporal region. (Damasio; Looking for Spinoza, 116)

Association cortex are areas in the frontal, parietal, and temporal lobes that are known to gather information from the senses and from elsewhere in the brain and link it together in potentially novel ways. (Andreasen; Creating Brain, 73)

Association cortex regions are the last to mature in human beings  They continue to develop new connections until around the early twenties in age. (Andreasen; Creating Brain, 73)

 

Modularity of Face Processing In Temporal Lobe Cortex

The entire network of temporal lobe face patches constitutes a dedicated brain system for the processing of one high-level object-category, faces. Structure and function are highly correlated. A face patch at a particular anatomical location harbors a specific face representation that is qualitatively different from the face representation in a face patch at a different location, and further differences are likely to exist between face representations in the different face patches. Thus, attaching a name to a given face patch has been shown to be meaningful because it signifies functional identity across individuals. Together with earlier results, this result shows that the face-processing system is a network composed of multiple, functionally specialized nodes.

 

Convergence Zones

A convergence zone is an ensemble of neurons within which many feedforward/ feedback loops make contact. (Koch, Neuronal Theories; 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. (Domasio; Convergence Zone, 71)

Both convergence regions and convergence zones come into existence under genetic control. (Domasio; Convergence Zone, 71)

A convergence zone is a means of establishing, through synaptic strengthening, preferred feedforward/feedback loops that use subsets of neurons within the ensemble. (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. (Domasio; Convergence Zone, 72)

Parcellated processing within the prefrontal cortex

The assignment of the central executive function to the prefrontal cortex is supported by substantial anatomical data. The phenomenal expansion, of the prefrontal area in primates and especially humans is impressively associated with the evolution of cognitive capacities. The prefrontal cortex in humans is a diverse area, composed of several distinct subdivisions. There is considerable consensus on correspondences in monkeys with identified areas in the human prefrontal cortex. Although several anatomical areas have been characterized based on morphological appearance, most of the functional evidence has been related to four general regions. These include the medial, dorsolateral, ventrolateral, and orbital areas. Most of the attention with regard to working memory functions in monkeys and humans has focused on the dorsolateral and ventrolateral areas, and these areas are partially distinct in their connections with more posterior parts of the cerebral cortex. Each of the subdivisions receives input from a diverse set of rostral and causal cortical areas, and each has a distinctive input pattern. (Eichenbaum; Neuroscience of Memory, 315ff)

Prefrontal areas are characterized by considerable associative connections with other prefrontal areas. The dorsolateral prefrontal area receives inputs mainly from medially and dorsolaterally located cortical areas that preferentially represent somatosensory and visuospatial information. Conversely, the lateral prefrontal areas receive inputs mainly from ventrolateral and ventromedial cortical areas that represent auditory and visual pattern information. (Eichenbaum; Neuroscience of Memory, 314)

There is considerable agreement that different posterior cortical areas are activated during modality-specific working memory processing. On the other hand, there is considerable controversy over whether different kinds of processing are parcellated within the prefrontal cortex, and about the nature of parcellation. (Eichenbaum; Neuroscience of Memory, 330)

 

 

Motor Cortex

Motion processing areas   (Koch; Quest for Consciousness, 139)

Posterior parietal cortex

Posterior parietal cortex, Action and Spacial Position  (Koch; Quest for Consciousness, 145)

Inferior temporal cortex

Inferior temporal cortex, Object Recognition  (Koch; Quest for Consciousness, 148)

Language processing areas

Language depends largely on left-hemisphere structures in more than 95% of people, including many left-handers.  (Damasio; Descartes’ Error, 66)

Broca area

Werneke area

 

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