Houk, et.al.; Models of Information Processing in the Basal Ganglia
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Houk; Info Process in Basal Ganglia and Cortex 3 Virtually the whole cerebral cortex projects to the basal ganglia, and outputs then funnel back to the frontal area of cortex, or in some cases, directly to motor systems in the midbrain and hindbrain.
Houk; Info Process in Basal Ganglia and Cortex 3 Diverse regions of cerebral cortex converge upon regions of striatum that, via pallidum and thalamus, project back to the region of frontal cortex that contributed to the striatal input. 0
Houk; Info Process in Basal Ganglia and Cortex 3 There is a shorter route from thalamus to striatum that bypasses the cerebral cortex. 0
Houk; Info Process in Basal Ganglia and Cortex 3 Topographic specificity within the pathways of basal ganglia and cortex. 0
Houk; Info Process in Basal Ganglia and Cortex 4 The input stage of the basal ganglia is the striatum, and the principal neurons of the striatum are called spiny neurons because of the great density of synaptic spines on their long dendrites. 1
Houk; Info Process in Basal Ganglia and Cortex 4 Each spiny neuron receives input from about 10,000 different afferent fibers, a remarkable degree of convergence that is second only to that for the Purkinje cells in the cerebellar cortex. 0
Houk; Info Process in Basal Ganglia and Cortex 5 Dopamine fibers provide a reinforcement input to the striatal spiny neurons that trains them to recognize patterns in their cerebral cortical input. 1
Houk; Info Process in Basal Ganglia and Cortex 5 Spiny neurons have abrupt thresholds between "up" and "down" states, owing to the highly nonlinear ionic properties of their membranes. 0
Houk; Info Process in Basal Ganglia and Cortex 5 These three features -- convergence of diverse inputs, specialized training signals, and dual-state behavior -- suggests that spiny neurons may be particularly well suited for pattern recognition tasks. 0
Houk; Info Process in Basal Ganglia and Cortex 5 The more diffuse dopamine input is assumed to function as a training signal that reinforces the synaptic weights of cortical and frontal neuron inputs to guide the pattern recognition process. 0
Houk; Info Process in Basal Ganglia and Cortex 5 Since reinforcement guides learning, the pattern that is eventually learned should reflect a context that is behaviorlly significant. 0
Houk; Info Process in Basal Ganglia and Cortex 6 Burst discharges of spiny neurons relate to a variety of contextual situations that the animal confronts in performing behavioral tasks. 1
Houk; Info Process in Basal Ganglia and Cortex 6 Assuming that a burst generated by a spiny neuron signifies the detection of a behaviorally significant context, the remainder of the circuit could then serve to refine this computation and deposit it in working memory for use in planning subsequent behavioral actions. 0
Houk; Info Process in Basal Ganglia and Cortex 6 Studies of patterns of persistent discharge in frontal cortical neurons appear to represent transitory, working memories of behaviorally significant stimuli or events. 0
Houk; Info Process in Basal Ganglia and Cortex 6 Patterns of persistent discharge in frontal cortical neurons provide distributed representations of contextual information consisting of stimulus features or internal states that need to be saved for short duration so that they can be used in controlling an ongoing behavioral action. 0
Houk; Info Process in Basal Ganglia and Cortex 6 A mechanism has been suggested whereby cortical-basal ganglionic modules might serve to detect the context of stimulus features or internal states and register them in working memory. 0
Houk; Info Process in Basal Ganglia and Cortex 6 Bursts of spiny neurons are known to produce a pause in the sustained inhibitory output from pallidal neurons. 0
Houk; Info Process in Basal Ganglia and Cortex 6 The burst in spiny neuron discharge, signifying the detection of a behaviorally significant context, produces a pause in pallidal neuron discharge, which through disinhibition, initiates sustained positive feedback in reciprocally-connected thalamic and frontal cortical neurons. 0
Houk; Info Process in Basal Ganglia and Cortex 6 The suggested cortical-basal ganglia mechanism can be thought of as a registration of the context detected by a spiny neuron into working memory, so that this information can be used later in the control of behavior. 0
Houk; Info Process in Basal Ganglia and Cortex 7 One way that working memories in the frontal cortex might be used to control behavior is via the extensive corticocortical pathways that lead, by many routes, to the primary motor cortex. 1
Houk; Info Process in Basal Ganglia and Cortex 7 The extensive corticocortical pathways to the primary motor cortex might be an effective way of initiating activity in the recurrent network that interconnects cerebellum, red nucleus, and motor cortex. Positive feedback in this network has been suggested as the main driving force for generating the motor commands that control limb movement. 0
Houk; Info Process in Basal Ganglia and Cortex 7 A second major output pathway to control behavior is via the pons to the cerebellum. This pathway might help to program the cerebellum to control an action. 0
Houk; Info Process in Basal Ganglia and Cortex 7 A third pathway to control behavior would be through corticostriatal inputs to different basal ganglionic modules, and this might permit the detection of one context, in the first module, to contribute to the detection of a subsequent context in another module. This recursive process could be a very powerful mechanism for generating complex properties that might be useful in high-level planning of actions. 0
Graybiel; Adaptive Neural Networks in Basal Ganglia 113 Effects of Basal Ganglia Processing on Action Plans. 106
Graybiel; Adaptive Neural Networks in Basal Ganglia 113 The output of the basal ganglia is directed mainly toward the brainstem and toward the frontal lobes. 0
Graybiel; Adaptive Neural Networks in Basal Ganglia 113 In the best-studied brainstem output system (the connection from the nigral pars reticulata to the superior colliculus) signals from the pars reticulata release the activity of neurons in the superior colliculus that participate in the initiation of saccadic eye movements. 0
Strick, et.al; Basal Ganglia Circuits 117 Macro-organization of the Circuits Connecting the Basal Ganglia with the Cortical Motor Areas. 4
Strick, et.al; Basal Ganglia Circuits 117 Circuits that link the basal ganglia with the skeletomotor areas in the frontal lobe.
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Strick, et.al; Basal Ganglia Circuits 117 Each cortical motor area projects most densely to a topographically distinct region of the caudate and putamen. 0
Strick, et.al; Basal Ganglia Circuits 117 Anatomical arrangement creates multiple "input channels" in the striatum. 0
Strick, et.al; Basal Ganglia Circuits 117 Each of these cortical areas appears to be influenced by projections from a topographically distinct region of the internal segment of the globus pallidus (GPi). 0
Strick, et.al; Basal Ganglia Circuits 117 Arrangement creates multiple "output channels" in GPi. 0
Strick, et.al; Basal Ganglia Circuits 117 Connections within the basal ganglia tend to connect the input channel related to a particular cortical area with the output channel that innervates the same cortical area. 0
Strick, et.al; Basal Ganglia Circuits 117 The underlying structural framework for basal ganglia interactions with the skeletomotor areas of the cerebral cortex is multiple "closed loops." 0
Strick, et.al; Basal Ganglia Circuits 117 The frontal lobe contains multiple motor areas involved in the generation and control of limb movement. 0
Strick, et.al; Basal Ganglia Circuits 117 Primary motor cortex receives input from at least six premotor areas in the frontal lobe. 0
Strick, et.al; Basal Ganglia Circuits 117 Two of the premotor areas in the frontal lobe are found on the lateral surface of the hemisphere (the dorsal premotor area [PMd] and the ventral enotor area JPMv]) and four of the premotor areas are found on the medial wall of the hemisphere (the supplementary motor area [SMA] and three cingulate motor areas buried in the banks of the cingulate sulcus). 0
Strick, et.al; Basal Ganglia Circuits 117 Each of the premotor areas projects not only to the primary motor cortex but also directly to the spinal cord. 0
Strick, et.al; Basal Ganglia Circuits 117 The number of corticospinal neurons in the premotor areas equals or exceeds the number in the primary motor cortex. 0
Strick, et.al; Basal Ganglia Circuits 117 Multiple parallel pathways from the frontal lobe can contribute to the generation of motor output. 0
Strick, et.al; Basal Ganglia Circuits 126 Clustering of output neurons that project to a common cortical area creates distinct output channels in the motor portion of GPi. 9
Strick, et.al; Basal Ganglia Circuits 128 Anatomical studies have provided considerable evidence that interconnections between the striatum, GPe, and GPi are largely along the radial dimension. 2
Strick, et.al; Basal Ganglia Circuits 128 Internal basal ganglia pathways tend to connect the input channel related to a. particular cortical area with the output channel innervating the same cortical area. 0
Strick, et.al; Basal Ganglia Circuits 128 The anatomical arrangement of internal basal ganglia pathways create a closed loop with the cerebral cortex, an underlying structural framework for basal ganglia interactions with the cerebral cortex. 0
Strick, et.al; Basal Ganglia Circuits 128 Many closed loops, each with a similar internal organization, interconnect the basal ganglia with different regions of the cerebral cortex. 0
Strick, et.al; Basal Ganglia Circuits 128 Determine what computational operation is performed in these basal ganglia loops that can be commonly applied to motor and nonmotor areas of the cerebral cortex. 0
Goldman-Rakic; Circuit Model of Working Memory 131 Multiple areas in the dorsolateral prefrontal cortex, in particular areas 8, 46, 12, and 45, play an essential role in what has been termed memory-guided performance. 3
Goldman-Rakic; Circuit Model of Working Memory 131 A memory process is the fundamental specialization of prefrontal cortex and the mechanism for directing responses by internal representations, which can be considered the basis for memory-guided responding. This process distinguishes the prefrontal contribution to behavior from those systems of the brain and cortex that guide behavior by associative processes, by sensory guidance, or by prepotent reflexive mechanisms. 0
Goldman-Rakic; Circuit Model of Working Memory 131 The associative processes, sensory guidance, and prepotent reflexive mechanisms are considered to be the province of.posterior association regions, including the hippocampal formation regions of the cerebrum, which have been accorded a major role in a large fraction of implicit and associatively learned behaviors and are considered the storage sites for the facts, events, instructions, concepts, rules, and habits that are the products of long-term conditioning and practice. 0
Goldman-Rakic; Circuit Model of Working Memory 131 Our contention is that the products of learning and past experience are accessed by prefrontal neurons which process them and amalgamate them with the ongoing stream of information that is currently being experienced. 0
Goldman-Rakic; Circuit Model of Working Memory 132 With respect to motor action, we should not fail to heed that the utterances of language, which are directed by purely representational processes and not by external stimuli, are guided by an on-line processor in one or more areas of the prefrontal cortex. 1
Goldman-Rakic; Circuit Model of Working Memory 132 There is ample evidence that the brain respects the distinction between associative, sensory-guided behavior and memory-guided, i.e., representationally guided responding. 0
Goldman-Rakic; Circuit Model of Working Memory 132 Here we focus on and propose some possible models of interaction between prefrontal circuits and components of basal ganglia circuitry. 0
Goldman-Rakic; Circuit Model of Working Memory 132 Prefrontal neurons have been shown to have "memory fields," that is, to increase their firing when a particular target, and only that target, disappears from view and has to be recalled several seconds later. 0
Goldman-Rakic; Circuit Model of Working Memory 132 Consistent with the concept of a memory field, delay activity in prefrontal neurons is tuned for the distance of a stimulus from the fovea as well as for its direction. 0
Goldman-Rakic; Circuit Model of Working Memory 132 The prefrontal neurons are activated solely during the time that the information is held "on line." As soon as a motor action based on that information is initiated, the neuron's activity returns to baseline. 0
Goldman-Rakic; Circuit Model of Working Memory 132 Memories for location of objects are mapped transiently in the prefrontal cortex, and new information is updated continually. 0
Goldman-Rakic; Circuit Model of Working Memory 132 Results provide strong evidence at a cellular level for a role of prefrontal neurons in representational processes, i.e., maintenance of information in the absence of the stimulus that was initially present. 0
Goldman-Rakic; Circuit Model of Working Memory 141 Both the substantia nigra and globus pallidus project via the thalamus back to the prefrontal cortex, parcelling feedforward projections onto clusters of cells in the thalamus. 9
Goldman-Rakic; Circuit Model of Working Memory 142 The compartmental nature of the descending part of the corticostriatal loop circuitry appears to be maintained in the ascending trajectory. 1
Goldman-Rakic; Circuit Model of Working Memory 142 The pattern is clearly one of compartmentalization in the feedforward projections of the paleostriatum to the thalamus. 0
Goldman-Rakic; Circuit Model of Working Memory 142 The thalamocortical system of connections should be considered separately from the corticostriatothalamocortical circuitry because it may serve a neural purpose -- both as a feedback and feedforward pathway to the cortex. 0
Goldman-Rakic; Circuit Model of Working Memory 142 Any theory of basal ganglia function will ultimately have to attend to the role played by the corticothalamic projections. 0
Goldman-Rakic; Circuit Model of Working Memory 142 By some accounts the corticothalamic innervation is as dense or denser than the thalamocortical connections. 0
Goldman-Rakic; Circuit Model of Working Memory 142 A corticothalamocortical reverberating circuitry may provide some of the amplification necessary to sustain delay period activation. 0
Goldman-Rakic; Circuit Model of Working Memory 142 Cells and dendrites in layer 4 and lower layer 3 of the prefrontal cortex could be studded with excitatory synapses from both the thalamus and from distant sensory associational cortical areas. 0
Goldman-Rakic; Circuit Model of Working Memory 143 A major theme running through the literature on the cortical control of motor action is the differentiation of two response-related neuronal activity patterns one that is tied to the preparation and organization of the movements themselves and one that is referenced to the target direction or goal of a movement, independent of the movement itself. Both types of coding are carried out by prefrontal neurons and are dissociable one from another. Thus, there are at least two types of pyramidal neuron with respect to motor programming and an inference can be made that they are connected by local circuitry. 1
Goldman-Rakic; Circuit Model of Working Memory 143 When behavior is memory-guided, a preparatory signal for a specified direction of eye movement originates first and foremost as a representation held, temporarily in prefrontal memory circuits as directional delay-period activity and then is transmitted locally to other prefrontal neurons, and to distant cortical and subcortical motor centers. 0
Goldman-Rakic; Circuit Model of Working Memory 144 In the case of a skeletal movement, the outflow would be to the basal ganglia, and to the premotor areas where it serves as a relay to primary motor cortex, or as a particular corticospinal outflow and hence a particular response of, a limb. 1
Goldman-Rakic; Circuit Model of Working Memory 144 Whenever the memory field of a prefrontal neuron in layer V is activated, presumably by corticocortical information flow, this directional information is presumably conveyed to the basal ganglia via the corticostriatal pathway. At the end of the delay, a phasic response heralds the initiation of a motor response by an average of 73 ms. At the same time, a signal can be recorded in the basal ganglia prior to a response with a median latency of 105 ms before the response. Neuronal activity in the substantia nigra is simultaneously depressed for about 100 ms by activation of the striatonigral projections. 0
Goldman-Rakic; Circuit Model of Working Memory 145 According to this model, corticopetal cells in layer V can influence (disinhibit) downstream neurons (basal ganglia; tectum) that will release an eye movement with particular direction and amplitude; cells in the same layer that output to the globus pallidus and premotor areas can exert the same type of motor control over forelimb movements. The important point is that the prefrontal neurons come into play only when these responses are genuinely memory-guided; when they are sensory-guided, the prefrontal cortex is dispensable and premotor circuits are sufficient. 1
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 Diseases primarily affecting the basal ganglia, such as Parkinson's disease (PD) and Huntington's disease (HD), lead to profound motor disorders. 132
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 In Parkinson's disease, patients exhibit tremor, rigidity, and akinesia as a consequence of cell death in the substantia nigra (around an 80% loss) and a resultant depletion of dopamine (DA) in the striatum (also about an 80% reduction). 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 HD patients, with primary lesions in the caudate and putamen, exhibit athetosis and chorea. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 Tourette's syndrome (TS), a chronic neurological disorder characterized by involuntary motor and phonic tics, is also a disease of the basal ganglia. TS patients show an abnormally large number of DA receptors in postmortem striatum, and abnormal volumes of caudate, putamen, and globus pallidus. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 There is a growing body of evidence from studies with PD, HD, and TS patients indicating that the basal ganglia play an important role in two forms of learning and memory -- skill learning and working memory. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 Although some PD patients exhibit depression or dementia, pervasive changes in intellectual ability do not appear to be necessary consequence of the disease. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 277 HD patients always develop a progressive dementia which results in pervasive deficits in cognition. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 283 Working memory is a multicomponent psychological system that supports the temporary storage, manipulation, and transformation of information, needed to perform cognitive tasks. 6
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 283 Working memory conducts interactions between perception of the outside world, long-term knowledge, and actions in the service of intelligent goals and plans. The three central features of this computational arena for processing and storing information are that (1) it has sharply limited resources; (2) it plays an increasingly vital role as a cognitive task becomes increasingly complex; and (3) it is used for the full range of high-level cognitive performance. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 283 The importance of DA for working memory in infrahuman primates raises the question of its role in human working memory. Patients with PD provide an opportunity to examine this issue, because PD primarily affects DA systems. PD patients, in fact, do perform poorly on a range of problem-solving (e.g., Tower of London, Wisconsin Card Sorting) and other tasks demanding the flexible shifting of strategy, especially when that shift must overcome habitual responses and when the strategy must be guided by internal plans rather than external cues. 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 288 What is the specific role of the basal ganglia in working memory? It is difficult to disentangle the specific contributions of the basal ganglia vs. frontal cortex to working memory, because the two brain regions may operate in such close functional concert. 5
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 289 Research results suggest that the critical contribution of the basal ganglia to working memory performance is mediated through psychomotor speed. 1
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 289 Skill learning and working memory are consistently impaired in patients with diseases of the basal ganglia. Both deficits are selective. For skill learning, HD patients showed intact mirror-tracing skill learning, but impaired rotary pursuit skill learning. On memory tests, PD, HD, and TS patients had intact performance on a recognition test, but impaired performance on a recall test more demanding of working memory. In broad terms, both the skill-learning and working memory deficits may reflect the importance of the basal ganglia for psychomotor sequencing performance, with different loops supporting sequencing in different domains (motor, cognitive). 0
Gabrieli; Basal Ganglia in Skill Learning and Working Memory 290 We may speculate that an essential contribution of the basal ganglia to human learning and memory is to support the speeded execution of component processes of a multistep cognitive or motor action. When that support is lost due to a basal ganglia disease, components are executed too slowly to accomplish either the smooth sequence of movements that characterizes perceptual-motor skill or the rapid sequence of thoughts that characterizes flexible working memory capacities., The idea that speed of execution can be vital for effective skill learning and efficient working memory can seem computationally mundane, but computers themselves have shown dramatically how processing speed alone can account for success or failure in accomplishing the goals of computations. 1
Jackson & Houghton; Basal Ganglia Model 338 Some researchers distinguish three functionally distinct neural networks which each appear to carry out separate but complementary operations involved in selective attention. 48
Jackson & Houghton; Basal Ganglia Model 338 Three selective attention networks include an anterior attention network (anterior cingulate and supplementary motor areas), which is related to volitional control and awareness, particularly awareness of target stimuli; a posterior attention network (posterior parietal cortex pulvinar and superior colliculus), which controls spatial orienting; and a vigilance network (locus coeruleus), which functions to place the anterior and posterior systems into an alert state, thereby enhancing attentional processing in both networks. 0
Jackson & Houghton; Basal Ganglia Model 338 The computational complexity of apparently simple behaviors is often only fully illustrated when we see how the normal system is impaired following damage or disease. 0
Jackson & Houghton; Basal Ganglia Model 338 Attentional dysfunction is associated with a wide range of neurological and psychiatric disorders, including schizophrenia (SZ), sensorimotor neglect, and Parkinson's disease (PD). 0
Jackson & Houghton; Basal Ganglia Model 338 Researchers have identified three functional components of covert orienting: a "disengage" function, a "move" function, and an "engage" function. 0
Jackson & Houghton; Basal Ganglia Model 338 The spatial precuing technique involves presenting subjects with some form of spatially informative cue which indicates the most probable location of an impending target. Such cues may take the form of a brief change in luminance in the vicinity of the target location, or may involve the use of symbolic cues to the target's location, such as a directional arrow. The effects of precuing are typically assessed by comparing response latency to targets appearing at a cued location (valid trials) against targets appearing at unexpected, i.e., noncued, locations. 0
Jackson & Houghton; Basal Ganglia Model 339 While spatial neglect has been reported following frontal lesions and from lesions to the basal ganglia, by far the most common lesion site to produce contralateral neglect for visual stimuli is the posterior parietal lobe. 1
Jackson & Houghton; Basal Ganglia Model 339 Although posterior parietal lobe patients may appear normal, they are frequently impaired in their ability to deal with a visual stimulus presented to their contralesional visual field, in circumstances where they are already attending to visual information. This impairment is revealed as a greatly magnified cost in reaction time to detect a visual target. 0
Jackson & Houghton; Basal Ganglia Model 341 Cortical nodes of the anterior and posterior attention networks are able to communicate with one another directly, via corticocortical pathways. 2
Jackson & Houghton; Basal Ganglia Model 341 Prefrontal and posterior parietal cortex are linked via topographically precise reciprocal connections, and both areas project to, and receive input from, other brain regions implicated in the control of visuospatial function. 0
Jackson & Houghton; Basal Ganglia Model 341 The cortical nodes of both the anterior and posterior attention networks receive catecholamine projections from subcortical sites implicated in the maintenance of an alert state (i.e., the locus coereuleus) and cortical nodes in both of the above networks can communicate with subcortical nodes, such as the superior colliculus, via direct excitatory projections which in all likelihood preserve spatiotopic information mapped within the cortex. 0
Jackson & Houghton; Basal Ganglia Model 341 In addition to direct connections between cortical and subcortical nodes, the anterior attentional system may modulate activity within the posterior attention network via third-party structures such as the basal ganglia. 0
Jackson & Houghton; Basal Ganglia Model 341 The basal ganglia structures include the caudate nucleus and putamen (jointly termed the striatum), the globus pallidus (lateral and medial segments), together with the substantia nigra, and subthalamic nucleus. 0
Jackson & Houghton; Basal Ganglia Model 341 Consistent with their anatomical location, the basal ganglia receive topographical projections from almost the entire neocortex, and project to frontal areas of the cortex via thalamocortical projections, and to certain subcortical structures, including the superior colliculus. 0
Jackson & Houghton; Basal Ganglia Model 341 Projections originating within frontal regions (e.g., frontal eye fields and Walker's area 46) and posterior parietal areas of the cortex terminate within the striatum in a series of alternating columns, thereby maintaining the topographical integrity of spatial information originating within these two areas, and perhaps allowing for the synthesis of spatial information originating from anterior and posterior areas of the cortex. 0
Jackson & Houghton; Basal Ganglia Model 341 While the basal ganglia may participate in the synthesis of some cortical information, other evidence suggests that the basal ganglia are organized into a number of largely separate corticostriatothalamocortical circuits, which appear to unite cortical and thalamic regions dedicated to a common function. 0
Jackson & Houghton; Basal Ganglia Model 342 It has been suggested that there at least five pathways, through the basal ganglia, each organized in parallel, and innervating different regions of the thalamus and frontal cortex. These include a "motor" circuit centered on the supplementary motor area and related regions of motor cortex, an "oculomotor" circuit centered on the frontal eye fields, and other circuits limbic, orbitofrontal, and dorsolateral prefrontal which are less obviously tied to the control of motor function. While each of these circuits, based on their cortical site of origin, appears to be dedicated to processing different kinds of information, the organization of each circuit follows a similar pattern, suggesting that the computational function of each circuit may be equivalent. 1
Jackson & Houghton; Basal Ganglia Model 342 When considering the computational function of the basal ganglia, it is of interest to note that unlike most other structures in the brain, the action of the basal ganglia is inhibitory. 0
Jackson & Houghton; Basal Ganglia Model 342 GABAergic neurons in the medial segment of the globus pallidus (GPm) and substantia nigra pars reticulata (SNr) are tonically active, and hold the thalamus and other structures (e.g., the superior colliculus), in a state of tonic inhibition. 0
Jackson & Houghton; Basal Ganglia Model 342 The basal ganglia pattern of inhibition is modulated via two distinct pathways, which appear to organized in opposition to each other, and link the striatum to output neurons in the GPm-SNr complex. One of these pathways, the striatonigral pathway, provides direct inhibitory modulation of activity in the SNr, while the other, the striatopallidal pathway, indirectly provides excitatory input to the GPm-SNr complex. Recent evidence has revealed important neurochemical differences between these two pathways, which appear under normal conditions to be sensitively balanced and to depend critically on modulation by dopamine. 0
Jackson & Houghton; Basal Ganglia Model 342 The basal ganglia complex can be characterized as an important component of several functionally and anatomically separate neural circuits which unite cortical and subcortical regions implicated in the processing of information in several behavioral domains. These circuits share a similar anatomical architecture, suggestive of a common computational function, and consist of two opposing pathways that respectively inhibit and facilitate the inhibitory output projections of the basal ganglia complex. Finally, these two opposing pathways are maintained in a delicate balance through modulation by dopamine. 0
Graybiel; Adaptive Neural Networks in Basal Ganglia