https://www.cell.com/trends/neurosciences/pdf/0166-2236(90)90107-L.pdf

Functional architecture of basal ganglia circuits: neural substrates of parallel processing

Schultz, Wolfram. Predictive reward signal of dopamine neurons. J. Neurophysiol. 80: 1–27, 1998. The effects of lesions, receptor blocking, electrical self-stimulation, and drugs of abuse suggest t...

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Predictive Reward Signal of Dopamine Neurons

The central theme of the "segregated circuits" hypothesis is that structural convergence and functional integration occurs within, rather than between, each of the identified circuits Admittedly, the anatomical evidence upon which this scheme is based remains incomplete The hypothesis continues to be predicated largely on comparisons of anterograde and retrograde labeling studies carried out in different sets of animals Only in the case of the "motor" circuit has evidence for the continuity of the loop been demonstrated directly in individual subjects; for the other circuits, such continuity is inferred from comparisons of data on different components of each circuit obtained in separate experiments Because of the marked compression of pathways leading from cortex through basal ganglia to thalamus, comparisons of projection topography across experimental subjects may be hazardous Definitive tests of the hypothesis of maintained segregation await additional double- and multiple-label tract-tracing experiments wherein the continuity of one circuit, or the segregation of adjacent circuits, can be examined directly in individual subjects It is worthy of note, however, that the few studies to date that have employed this methodology have generated results consistent with the segregated circuits hypothesis Moreover, single cell recordings in behaving animals have shown striking preservation of functional specificity at the level of individual neurons throughout the "motor" and "oculomotor" circuits It is difficult to imagine how such functional specificity could be maintained in the absence of strict topographic specificity within the sequential projections that comprise these two circuits This is not to say, however, that we expect the internal structure of functional channels (eg, the "arm" channel within the "motor" circuit) to have cable-like, point-to-point topography When the grain of analysis is sufficiently fine, anatomical studies have shown repeatedly that the terminal fields of internuclear projections (eg, to striatum, pallidum, nigra, thalamus, etc) often appear patchy and highly divergent, suggesting that neighboring groups of projection cells tend to influence interdigitating clusters of postsynaptic neurons While more intricate and complex than simple point-to-point topography, however, this type arrangement should also be capable of maintaining functional specificity As discussed briefly above, it is not yet clear to what extent the inputs to the "motor" circuit from the different precentral motor fields (eg, MC, SMA, APA) are integrated in their passage through the circuit It now appears that at the level of the putamen such inputs remain segregated(ABSTRACT TRUNCATED AT 400 WORDS)

Basal ganglia-thalamocortical circuits: parallel substrates for motor, oculomotor, "prefrontal" and "limbic" functions.

http://www.columbia.edu/itc/gsas/g9600/2003/JavitchReadings/Schultz(Sulzer).pdf

Getting Formal with Dopamine and Reward

The basal ganglia: focused selection and inhibition of competing motor programs.

Neurons in the arm areas of the external and internal segments of the globus pallidus (GPe and GPi) and the ventral pallidum (VP) have been examined in a visuomotor step-tracking task. This task, which was similar to that used previously to examine neurons in the arm area of the putamen, dissociated the direction of movement from the pattern of muscle activity associated with the movement. The major finding of the present study is that, as in the putamen, the activity of almost half of the neurons in GPe and GPi was related to the direction of movement. Cells with overall patterns of activity similar to muscle were rare, although many neurons had static and/or dynamic load effects which resembled those seen in muscle. Responses of neurons to load application have also been examined in this paradigm in order to determine the nature of possible somatosensory input. Short-latency “sensory” responses to load application were found in pallidum as previously in putamen, but, by contrast, they occurred somewhat later and included bidirectional responses. Similar proportions of cells in GP and putamen were related to static loads. Some VP neurons appeared to encode information about specific features of the trials, but the majority of responses were nonspecific suggesting relations to more general features of the task.

The primate globus pallidus: neuronal activity related to direction of movement

Recent anatomic and physiologic studies have shed new light on the functional organization of the basal ganglia and their role in movement. The basal ganglia receive topographically organized input from the entire neocortex. Influences from sensorimotor and "association" cortices appear to remain segregated in the basal ganglia. The concept of segregated parallel subcortical loops subserving "motor" and "complex" functions is discussed. Recent neurophysiologic studies in behaving primates suggest that basal ganglia output plays a role in controlling the direction and amplitude of movement but is not primarily involved in the initiation of limb movement or selection of specific muscles. These studies are generally consistent with data from patients with Parkinson's disease, which likewise indicates a deficit in the programming of movement amplitude in step-tracking tasks, with little or no change in reaction-time or pattern of muscular activity.

Role of basal ganglia in limb movements.

Studies of single-cell discharge in the basal ganglia of behaving primates have revealed: characteristic patterns of spontaneous discharge in the striatum, external (GPe) and internal (GPi) globus pallidus, pars reticulata and pars compacta of the substantia nigra, and the subthalamic nucleus (STN); phasic changes in neural discharge in relation to movements of specific body parts (e.g. leg, arm, neck, face); short-latency (sensory) neural responses to passive joint rotation; a somatotopic organization of movement-related neurons in GPe, GPi, and STN; a clustering of functionally similar neurons in the putamen and globus pallidus; greater representation of the proximal than of the distal portion of the limb; changes in neural activity in reaction-time tasks, suggesting a greater role of the basal ganglia in the execution than in the initiation of movement in this paradigm; a clear relation of neuronal activity to direction, amplitude (?velocity) of movement, and force; a preferential relation of neural activity to the direction of movement, rather than to the pattern of muscular activity. Some of these findings suggest that the basal ganglia may play a role in the control of movement parameters rather than (or independent of) the pattern of muscular activity. Loss of basal ganglia output related to amplitude may account for the bradykinesia in Parkinson's disease. The presence of somatotopic organization in the putamen and globus pallidus, together with known topographic striopallidal connections, suggests that segregated, parallel cortico-subcortical loops subserve 'motor' and 'complex' functions.

Functional organization of the basal ganglia: contributions of single-cell recording studies.

Publisher Summary This chapter primarily describes the role of the basal ganglia in the control of limb movements. Data from recent anatomical and behavioral/neurophysiological studies in primates is emphasized. The results of recent neurophysiologic studies in trained primates suggest that, basal ganglia output may play a role in scaling the amplitude of step movements by its effects on the magnitude of agonist EMG activity, but that it is not primarily involved in the initiation of limb movement in a reaction time task or in the selection of specific muscles. These studies are generally consistent with the available data on limb movements, in patients with Parkinson's disease. This consistency indicates major deficit in the control of movement amplitude in step-tracking tasks with little or no impairment of reaction time or disruption of the pattern of muscular activity. Evidence for a role of the basal ganglia in the preparation for movements has recently been determined. A role in other aspects of movement, such as motor programming and “complex” behavior, appears likely to be based on both anatomical and physiological data.

The contribution of basal ganglia to limb control

The activity of neurons in the nucleus basalis of Meynert (nbM), both the compact (nbMc) and interstitial (nbMi) components, has been examined in monkeys trained to perform a visuomotor step-tracking task. This study was carried out in the same animals and with the same task used to examine neuronal activity in the external and internal segments of globus pallidus (GPe and GPi) and ventral pallidum (VP). The presumed interstitial cells that are located within the laminae surrounding GPe and GPi and identified physiologically by their similarity with nbMc neurons, are referred to as border cells. A major finding of this study is that a large proportion of nbMc and border cells were active in relation to either the step-tracking movements or to load application. Moreover, a high proportion of the responses of border neurons were differential for opposite directions of load and movement. The percentages of directionally specific border and nbMc neurons were considerably less than for GP, with border neurons having more directionally specific responses than nbMc neurons. The similarity between border and GP neuronal properties in this task suggests that both may receive similar sensorimotor afferent input. In the compact portion of nbM, nonspecific neuronal responses following each behavioral event in the paradigm were common. These responses appeared to have been modified by and may have been contingent upon association with reinforcement.

S. J. Mitchell

Papers

The primate globus pallidus: neuronal activity related to direction of movement

Role of basal ganglia in limb movements.

Functional organization of the basal ganglia: contributions of single-cell recording studies.

The contribution of basal ganglia to limb control

The primate nucleus basalis of Meynert: neuronal activity related to a visuomotor tracking task.