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

Basal Ganglia

Basal ganglia are a set of huge nuclei in the depths of the forebrain that have to do with movement. The relationships among the nuclei of the basal ganglia are by no means completely understood.

Circuitry linking various neural subregions that collectively form the basal ganglia are so complex and convoluted that computer models are required to gain insight. (Frank; Learning and the Basal Ganglia, 154)

Planning-tuning-motor output of the basal ganglia and cerebellum are input to the cortex via the thalamus. (Arbib - Handbook of Brain Theory and Neural Networks; Mumford; Thalamus, 981)

The basal ganglia represent some of the least understood areas of the brain, particularly in regard to their functional organization and architecture. (Llinás; I of the Vortex, 136)

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. (Strick, et.al; Basal Ganglia Circuits, 128)

Basal ganglia consist of a set of large nuclei deep in the brain that receive connections from much of the cortex, go through a series of successive synaptic steps, and then project to the thalamus and from there back to the cortex. Basal ganglia are involved in the planning and execution of complex motor and cognitive acts and are dysfunctional in Parkinson's and Huntington's diseases. (Edelman; Universe of Consciousness, 45)

 

Research Study — Basal Ganglia Circuit for Evaluating Action Outcomes

Research Study  —  Basal Ganglia to Frontal Cortex Direct Connection

 

Basal Ganglia Model

A basal ganglia model reported in 2013 provides an informative statement of basal ganglia functionality.

 Research Study — Basal Ganglia Model

 Research Study — Basal Ganglia Direct and Indirect Pathways

Earlier research by Michael Frank provides consistent interpretations with these recent results:

The circuit to the frontal cortex enables the basal ganglia to transform and amplify the pattern of neural firing in the frontal cortex that is associated with adaptive, or appropriate behaviors, while suppressing those that are less adaptive.(Frank; Learning and the Basal Ganglia, 152)

Basal ganglia may be involved in choices and initiations of output    during planning of successions of motor programs;    main activity is in short time periods, between 300 msec and several seconds. (Edelman; Remembered Present, 139)

 

Modeling the Basal Ganglia

Basal ganglia receive information from the frontal cortex about behavior that is being planned for a particular situation. Basal ganglia affect activity in the frontal cortex through a series of neural projections that ultimately go back to the same cortical areas from which they received the initial input. (Frank; Learning and the Basal Ganglia, 152)

Many attempts have been made to a model basal ganglia function. Circuitry linking various neural subregions that collectively form the basal ganglia are so complex and convoluted that computer models are required to gain insight. (Frank; Learning and the Basal Ganglia, 154)

A number of computer models of the basal ganglia have converged on the same core idea: the architecture of the basal ganglia are particularly well  suited to support  "action selection" -- that is, to implicitly weigh all available options for what to do next and to choose the best one. (Frank; Learning and the Basal Ganglia, 154)

Actions that can be selected by the basal ganglia range from simple motor behaviors, to manipulation of information in memory, such as multiplying numbers in your head. (Frank; Learning and the Basal Ganglia, 154)

 

Research study — Basal Ganglia loops for Action Selectionmany loops through the basal ganglia, each regulate the embodiment of pattern formation in a given area of cerebral cortex.

 

Connections to the Basal Ganglia

Basal ganglia do not have direct input or output connections with the spinal cord. (Kandel; Principles of Neural Science, 853)

The large-scale organization of the basal ganglia can be viewed as a family of reentrant loops that are organized in parallel, each taking its origin from a particular set of functionally related cortical fields, passing through the functionally corresponding portions of the basal ganglia, and returning to parts of those same cortical fields by way of specific basal ganglia recipient zones in the dorsal thalamus. (Alexander; Basal Ganglia, 139)

Basal ganglia receive inputs from all parts of the cerebral cortex but send their output only to the frontal lobe through the thalamus. (Kandel; Principles of Neural Science, 331)

Outputs of the basal ganglia go to all areas of the frontal cortex, placing the basal ganglia in a position to influence a wide variety of behaviors. (Squire; Fundamental Neuroscience, 834)

Motor functions of the basal ganglia are mediated, in large part, by the motor areas of the frontal cortex. (Kandel; Principles of Neural Science, 853)

Positive feedback is sometimes transmitted by way of disinhibition, went two inhibitory stations are connected in series. This type of positive feedback characterizes the corticocortical loop through the basal ganglia. (Schuz; Neuroanatomy Computational, 623)

Basal ganglia receive their primary input from the cerebral cortex and send their output to the brain stem and, via the thalamus, back to the prefrontal, premoter, and motor cortices. (Kandel; Principles of Neural Science, 853)

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)

Activity within the basal ganglia is initiated at cortical levels. (Afifi; Functional Neuroanatomy, 290)

 

Research Study — Basal Ganglia Homology with Arthropod Central Complex

 

Basal Ganglia Activate the Preparatory Phase for Next Movement

The normal routine activity of the basal ganglia may promote automatic execution of routine movement by facilitating the desired cortically driven movements and suppressing unwanted muscular activity. (Philip Lieberman; Human Language, 94)

Basal ganglia activate the preparatory phase for the next movement, thereby switching between components of the motor sequence. (Philip Lieberman; Human Language, 92)

The supplementary motor area receives its dominant input from the ventral lateral thalamus, which in turn receives projections almost exclusively from the globus pallidus -- the major output unit of the basal ganglia. (Philip Lieberman; Human Language, 92)

The internal cueing mechanism between basal ganglia and supplementary motor area would coordinate the switch between motor components at the appropriate time, thus controlling the timing of submovement initiation. (Philip Lieberman; Human Language, 92)

Basal Ganglia Involved in Non-Motor Functions

The role of the basal ganglia in controlling movement must give insight into their other functions, particularly if thought is mental movement without motion. (Philip Lieberman; Human Language, 94)

Basal ganglia have been implicated in a variety of non-motor disorders, including depression, obsessive-compulsive disorder, attention deficit hyperactivity disorder, and schizophrenia. (Squire; Fundamental Neuroscience, 834)

 

Striatum the major recipient of Inputs to the Basal Ganglia

Striatum is the major recipient of inputs to the basal ganglia from the cerebral cortex, thalamus, and brain stem. (Kandel; Principles of Neural Science, 855)

Each area of the neocortex projects to a discrete region of the striatum and does so in a highly topographic manner. (Kandel; Principles of Neural Science, 858)

Striatum also receives excitatory inputs from the intralamina nuclei of the thalamus, dopaminergic projections from the midbrain, and serotonergic input from the raphe nuclei. (Kandel; Principles of Neural Science, 856)

Striatum consists of three subdivisions: (1) caudate nucleus, (2) putamen, and (3) ventral striatum (which includes the nucleus accumbens). (Kandel; Principles of Neural Science, 855)

Striatum neurons project to the globus pallidus and substantia nigra. (Kandel; Principles of Neural Science, 855)

Globus pallidus and substantia nigra give rise to the major output projections from the basal ganglia. (Kandel; Principles of Neural Science, 855)

 

Many Routes to Behavioral Output

The general view that there are many routes to behavioral output is supported by the evidence that there are many input systems to the basal ganglia (from almost all areas of the cerebral cortex), and that neuronal activity in each part of the striatum reflects the activity in the overlying cortical area. (Rolls; Emotion Explained, 401)

Actions that can be selected by the basal ganglia range from simple motor behaviors, to manipulation of information in memory, such as multiplying numbers in your head. (Frank; Learning and the Basal Ganglia, 154)

Actions that are relatively automatic could involve control of behavior by brain systems that are old in evolutionary terms such in the basal ganglia. (Rolls; Emotion Explained, 401)

General view of brain evolution in which, as areas of the cortex evolved, they are laid on top of the existing circuitry connecting inputs to outputs, and in which each level in this hierarchy of separate input and output data pathways may control behavior according to the specialized function it can perform. (Rolls; Emotion Explained, 403)

Neurons in the basal ganglia regulate movement and contribute to certain forms of cognition such as the learning of skills. (Kandel; Principles of Neural Science, 331)

In addition to the response selection function by competition, the basal ganglia may enable signals originating from non-motor parts of the cerebral cortex to be mapped onto motor signals to produce behavioral output. (Rolls; Brain and Emotion, 191)

Basal ganglia are involved in the Fixed Action Patterns (FAPs) of muscular movements of spoken language. FAPs of spoken language are established as synaptic strengths formed in the speech development of infancy and early childhood.

Action of the Basal Ganglia Is Inhibitory

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. (Jackson & Houghton; Basal Ganglia Model, 342)

The two output nuclei of the basal ganglia, the internal pallidal segment and the substantia nigra pars reticular, tonically inhibit their target nuclei in the thalamus and brain stem. (Kandel; Principles of Neural Science, 856)

Neurons in the two output nuclei of the basal ganglia discharge tonically at high frequency. (Kandel; Principles of Neural Science, 857)

When excitatory inputs transiently activate the direct pathway from the striatum to the pallidum, tonically active neurons in the pallidum are briefly suppressed, permitting the thalamus and ultimately the cortex to be activated. (Kandel; Principles of Neural Science, 857)

Dopaminergic inputs to the two pathways lead to the same effect -- reducing inhibition of the thalamocortical neurons and thus facilitating movements initiated in the cortex. (Kandel; Principles of Neural Science, 857)

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. (Jackson & Houghton; Basal Ganglia Model, 342)

Overall, excitation of neostriatal spiny neurons leads to a disinhibition of the otherwise suppressed activity of neurons in the thalamus and superior colliculus. (Wilson; Basal Ganglia, 373)

Output of the Basal Ganglia Is Analogous to a Brake

Brake metaphor is modified in a 2013 Basal Ganglia Model.

When a movement is initiated by particular motor pattern generator, GPi neurons projecting to that generator decrease their discharge, thereby removing the tonic inhibition and "releasing the break" on that generator. (Squire; Fundamental Neuroscience, 833)

GPi neurons projecting to other movement pattern generators increase their firing rate, thereby increasing inhibition and applying a "brake" on those generators. (Squire; Fundamental Neuroscience, 834)

 

Basal Ganglia Connected to Cortex Via Parallel Pathways

The basal ganglia are a set of subcortical structures connected to the cortex via a group of parallel, unidirectional pathways illustrated in Edelman’s diagram.

The general connectivity through the basal ganglia is for cortical or limbic inputs to reach the striatum, which then projects to the globus pallidus and substantia nigra, which in turn project by the thalamus back to the cerebral cortex.  Within this overall scheme, there are a set of at least partially segregated parallel processing streams. (Rolls & Treves; Neural Networks, 206)

Each cortical motor area projects most densely to a topographically distinct region of the caudate and putamen. (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. (Strick, et.al; Basal Ganglia Circuits, 117)

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. (Jackson & Houghton; Basal Ganglia Model, 341)

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. (Jackson & Houghton; Basal Ganglia Model, 342)

 

Link to — Basal Ganglia multiple loops diagram multiple inhibitory loops of the basal ganglia are funneled onto relatively small nuclei of the thalamus.

 

The intricate inhibitory and excitatory connections of the basal ganglia are shown in a Parallel Pathways Diagram.

Subcortical parallel pathways of basal ganglia and cerebellum constitute one of the three topological networks of the brain.

Basal ganglia receive a broad spectrum of cortical inputs. (Squire; Fundamental Neuroscience, 816)

Basal ganglia receive inputs from all parts of the cerebral cortex but send their output only to the frontal lobe through the thalamus.  (Kandel; Principles of Neural Science, 331)  (Edelman’s diagram)

Major Components of the Basal Ganglia

Major components of the basal ganglia are: (1) caudate nucleus, (2) putamen, (3) globus pallidus. (Kandel; Principles of Neural Science, 331)

Four principal nuclei of the basal ganglia are: (1) striatum, (2) globus pallidus, (3) substantia nigra (consisting of pars reticulata and pars compacta), and (4) subthalamic nucleus. (Kandel; Principles of Neural Science, 855)

Striatum consists of three subdivisions: (1) caudate nucleus, (2) putamen, and (3) ventral striatum (which includes the nucleus accumbens). (Kandel; Principles of Neural Science, 855)

Striatum is the major recipient of inputs to the basal ganglia from the cerebral cortex, thalamus, and brain stem. (Kandel; Principles of Neural Science, 855)

Damage to the striatum produces effects which suggests that it is involved in orientation to stimuli and to initiation and control of movement. (Rolls & Treves; Neural Networks, 209)

 

Link to — Striatum ModelHypothesis that the striatum serves as part of an adaptive motor control system.

 

References to Diagrams of the Basal Ganglia

Basic circuits of the basal ganglia, excitatory and inhibitory connections.  (Diagram) (Purves; Neuroscience, 418)

Anatomical organization of inputs to the basal ganglia, caudate and putamen. - (diagram) (Purves; Neuroscience, 419)

Functional organization of outputs from the basal ganglia - (diagram) (Purves; Neuroscience, 422)

Input to the Basal Ganglia

The basal ganglia receive inputs from all parts of the cerebral cortex, including the motor cortex, and have outputs directed strongly toward the premotor and prefrontal cortex by which they could influence movement initiation. (Rolls & Treves; Neural Networks, 206)

Caudate and putamen of the corpus striatum comprise the input zone of the basal ganglia. (Purves; Neuroscience, 417)

Functionally distinct pathways project parallel from the cortex to the striatum. (Purves; Neuroscience, 420)

Each cortical motor area projects most densely to a topographically distinct region of the caudate and putamen. (Strick, et.al; Basal Ganglia Circuits, 117)

Anatomical arrangement creates multiple "input channels" in the striatum. (Strick, et.al; Basal Ganglia Circuits, 117)

The fact that different cortical areas project to different regions of the striatum implies that the corticostriatal pathway consists of multiple parallel pathways serving different functions. (Purves; Neuroscience, 419)

The underlying structural framework for basal ganglia interactions with the skeletomotor areas of the cerebral cortex is multiple "closed loops." (Strick, et.al; Basal Ganglia Circuits, 117)

Nearly all regions of the neocortex project directly to the striatum, making the cerebral cortex the source of the largest input to the basal ganglia, by far. (Purves; Neuroscience, 418)

Large dendritic trees of the striatum allow them to integrate inputs from a variety of cortical, thalamic, and brainstem structures. (Purves; Neuroscience, 418)

Of the cortical areas that innervate the striatum, the heaviest projections are from association areas in the frontal and parietal lobes, but substantial contributions also arise from the temporal, insular, and cingulate cortices. (Purves; Neuroscience, 418)

Output from the Basal Ganglia

The output of the basal ganglia is directed mainly toward the brainstem and toward the frontal lobes. (Graybiel; Adaptive Neural Networks in Basal Ganglia, 113)

Globus pallidus and substantia nigra pars reticulata are the main sources of output from the basal ganglia complex. (Purves; Neuroscience, 418)

Outputs of the globus pallidus and substantia nigra directed via the thalamus to motor regions such as a supplementary motor cortex and the premotor cortex potentially provide important output routes for the basal ganglia to produce actions. (Rolls; Brain and Emotion, 197)

Efferent neurons of the internal globus pallidus and substantia nigra pars reticulata together give rise to the major pathways that link the basal ganglia with upper motor neurons located in the cortex and in the brainstem. (Purves; Neuroscience, 423)

Pathway to the cortex arises primarily in the internal globus pallidus and reaches the motor cortex after a relay in the ventral anterior- and ventral lateral-nuclei of the dorsal thalamus. These thalamic nuclei project directly to motor areas of the cortex, thus completing a vast loop that originates in multiple cortical areas and terminates (after relays in  the basal ganglia and thalamus) back in the motor areas  of the frontal lobe. (Purves; Neuroscience, 423)

Because efferent cells  of both the globus pallidus and substantia nigra pars reticulata are GABAergic, the main output of the basal ganglia is inhibitory. In contrast to the quiescent medium spiny neurons, the neurons in both these output zones have  high levels of spontaneous activity that tend to prevent unwanted movements by tonically inhibiting cells in the superior colliculus and thalamus. (Purves; Neuroscience, 423)

 

 

 

(paraphrase:   Basal ganglia loops and non-motor brain functions, Purves; Neuroscience, 432)

Traditionally, the basal ganglia have been regarded as motor structures that regulate the initiation of movements.  However, the basal ganglia are also central structures in anatomical circuits or loops that are involved in modulating non-motor aspects of behavior.  These parallel loops originate in broad regions of the cortex, engage specific subdivisions of the basal ganglia and thalamus, and ultimately terminate in areas of the frontal lobe outside of the primary motor and premotor cortices.  These non-motor loops include a “prefrontal” lobe involving the dorsal lateral prefrontal cortex and part of the caudate, a limbic loop involving the cingulate cortex and the ventral striatum and an “oculomotor” loop that modulates the activity of the frontal eye fields.

The anatomical similarity of these loops to the traditional motor loops suggests that the non-motor regulatory functions of the basal ganglia may be generally the same as what the basal ganglia do in regulating the initiation of movement.  For example, the prefrontal lobe may regulate the initiation and termination of cognitive processes such as planning, working memory, and attention.  The limbic loop may regulate emotional behavior and motivation.  Variation of cognitive and emotional functions in both Huntington's disease and Parkinson's disease could be the result of disruption of these nonmotor loops.

A variety of other disorders are now thought to be caused at least in part by damage to nonmotor complements of the basal ganglia.  For example, patients with Tourette's syndrome produce inappropriate utterance and obscenities as well as unwanted vocal as vocal motor “tics” and repetitive grunts.  These manifestations may be the result of excessive activity in basal ganglia loops that regulate the cognitive circuitry of the prefrontal speech areas.

(end of paraphrase)

 

Two Functions of Basal Ganglia

In my view, there are two functions of the basal ganglia:

(1) Restraint of FAPs

Rapid response movements are sometimes needed. An animal may need to flee from danger or to pounce upon prey. Restrained but continuously running FAPs in the basal ganglia and brain stem, together with reflexes in the spinal cord, can provide rapid-response actions.

Restrained by inhibitory neural circuits

Jack-in-the-Box metaphor: in a simplistic metaphor, restrained FAPs are like a Jack-in-the-Box, latched by the basal ganglia.  Signals from the motor cortex release the latch on the Jack-in-the-Box, and the FAPs spring into action rapidly.  The impulsive actions of the FAPs is dampened and smoothed by the modulating actions of the cerebellum as well as the basal ganglia.

Brain is a jack-in-the-box, loaded to the brim with spring-loaded plans of action. (Hobson; Dreaming as Delirium, 117)

(2) Participate with the cortex to synthesize action plans

The cortex and basal ganglia can conjure action plans related to movement and perhaps other things.

Parallel loops through the basal ganglia (and through the cerebellum) may be involved in setting up and executing neural routines. (Edelman; Universe of Consciousness, 185)

Brain’s function as a reality emulator for prediction and action.

Brain selects among multiple possible actions (FAPs) facilitated by Basal Ganglia

Cognitive models have been focusing on how dopamine signals in the basal ganglia, which occur as a result of positive and negative outcomes of decisions (that is, rewards and punishments), drive learning. Basal ganglia learning is made possible by two main types of dopamine receptors, D1 and D2, which are associated with two separate neural pathways through the basal ganglia. When the "Go" pathway is active, it facilitates an action directed by the frontal cortex; when the opposing "NoGo" pathway is more active, the action is suppressed. These Go and NoGo pathways compete with each other when the brain selects among multiple possible actions, so that an adaptive action can be facilitated while at the same time competing actions are suppressed. (Frank; Learning and the Basal Ganglia, 155)

 

Science 3 July 2009: Vol. 325. no. 5936, pp. 48 - 50

How to Think, Say, or Do Precisely the Worst Thing for Any Occasion

Daniel M. Wegner

Department of Psychology, Harvard University, 33 Kirkland Street, Cambridge, MA 02138

In slapstick comedy, the worst thing that could happen usually does: The person with a sore toe manages to stub it, sometimes twice. Such errors also arise in daily life, and research traces the tendency to do precisely the worst thing to ironic processes of mental control. These monitoring processes keep us watchful for errors of thought, speech, and action and enable us to avoid the worst thing in most situations, but they also increase the likelihood of such errors when we attempt to exert control under mental load (stress, time pressure, or distraction). Ironic lapses of mental control often appear when we attempt to be socially desirable, as when we try to keep our minds out of the gutter. People instructed to stop thinking of sex, for example, show greater arousal during the suppression of sex thoughts. Ironic errors in attention and memory occur with identifiable brain activity and prompt recurrent unwanted thoughts; attraction to forbidden desires; expression of objectionable social prejudices; production of movement errors; and rebounds of negative experiences such as anxiety, pain, and depression. Such ironies can be overcome when effective control strategies are deployed and mental load is minimized.

 

Basal ganglia respond rapidly to cortical commands for movement

Animals must have capability for movement, which must be readily available on a quick-reaction basis. Rather than having the physiological delay of a movement initiation sequence, the movement sequences are constantly available as circulating neural signals of inhibited FAPs. Cortical commands for movement respond rapidly by releasing the appropriate inhibited FAPs.

Activity in the basal ganglia is running all the time, playing motor patterns and snippets of motor patterns amongst and between themselves. Because of the reentrant inhibitory connectivity among and between these nuclei, they seem to act as a continuous, random, motor pattern generator. (Llinás; I of the Vortex, 170)

Expression of FAPs is supported by the interplay among a number of vastly different parts of the nervous system and the basal ganglia. (Llinás; I of the Vortex, 136)

Majority of connections within the basal ganglia are inhibitory. (Llinás; I of the Vortex, 138)

Basal ganglia's intrinsic, reciprocal inhibitory activity keeps all potential FAPs from becoming active. (Llinás; I of the Vortex, 138)

When a FAP is executed, we say that it has been "liberated" into action. (Llinás; I of the Vortex, 138)

Basal ganglia are the doors that, when unlatched by the motor cortex, may release into action very large functions outside of the basal ganglia. (Llinás; I of the Vortex, 138)

FAPs are most probably implemented at the level of the basal ganglia and put into context by the reentry of the basal ganglia output into the ever-cycling thalamocortical system. (Llinás; I of the Vortex, 144)

Language itself is a FAP. (Llinás; I of the Vortex, 151)

 

Internal competition among ancient evolutionary mutations

The basal ganglia are ancient evolutionary developments. Reptiles that have tiny cortical areas have a developed basal ganglia.

In vertebrates with no or only poorly developed cortex, the basal ganglia are the most important forebrain centers. (Koch; Quest for Consciousness, 130)

Basal ganglia pathways are complicated. The complication is the result of internal competition among multiple pathways that developed from ancient mutations. Over evolutionary time, ancient multiple pathways interact and compete in the natural selection process. The result is there are some top-performing pathways together with a number of lesser-performing pathways that nonetheless contribute in ways that aid survival. The multiple pathways tend to enhance reliability characteristics that avoid complete failure in case functionality in one of the pathways should fail.

Inhibitory effect of the Basal Ganglia

Although there are many different neurotransmitters used within the basal ganglia (principally ACh, GABA, and dopamine), the overall effect on thalamus is inhibitory. The function of the basal ganglia is often described in terms of a "brake hypothesis". To sit still, you must put the brakes on all movements except those reflexes that maintain an upright posture. To move, you must apply a brake to some postural reflexes, and release the brake on voluntary movement. In such a complicated system, it is apparent that small disturbances can throw the whole system out of whack, often in unpredictable ways. The deficits tend to fall into one of two categories: the presence of extraneous unwanted movements or an absence or difficulty with intended movements.

 

FAPs implemented by basal ganglia

FAPs are most probably implemented at the level of the basal ganglia and put into context by the reentry of the basal ganglia output into the ever-cycling thalamocortical system. (Llinás; I of the Vortex, 144)

Dysfunctions of FAPs release from the Basal Ganglia

One way to gain some understanding of the basal ganglia is to consider the neurological dysfunctions of Parkinson's disease and Tourette’s Syndrome. In Parkinson's disease there is difficulty initiating movement, i.e., releasing (“unbraking”) FAPs from the basal ganglia. In Tourette’s Syndrome certain FAPs are released involuntarily.

Basal ganglia diseases produce severe deficits of movement. Parkinson's disease, movements are more difficult to make. Huntington's disease, useless and unintended movements interfere with intended ones. (Shepherd; Synaptic Organization of the Brain, 329)

Basal Ganglia anatomy, connections, functionality

Basal Ganglia, (Wilson; Basal Ganglia, 329)

Major structures of the basal ganglia are the caudate nucleus, putamen, globus substantia nigra, and subthalamic nucleus, (Wilson; Basal Ganglia, 329)

Basal ganglia anatomy. (Pinel; Anatomy of Human Brain, 124)

Basal ganglia have no direct connections with either the sensory or motor organs. (Wilson; Basal Ganglia, 329

Anatomical connections of the basal ganglia link it to elements of the sensory, motor, cognitive, and motivational apparatus of the brain, (Wilson; Basal Ganglia, 329)

Basal Ganglia Parallel Circuit Diagram

Basal ganglia diseases produce severe deficits of movement. Parkinson's disease, movements are more difficult to make. Huntington's disease, useless and unintended movements interfere with intended ones, (Wilson; Basal Ganglia, 329)

Only voluntary, purposive movements affected, reflexive movements relatively unaffected, (Wilson; Basal Ganglia, 329)

Two largest sources of input to the basal ganglia: cerebral cortex and thalamus, (Wilson; Basal Ganglia, 329)

Most of the input to the basal ganglia from other brain structures arrives in the neostriatum, which consists of the caudate nucleus, putamen, and nucleus accumbens, (Wilson; Basal Ganglia, 329)

Within the caudate nucleus and the putamen, inputs from sensory, motor; and association cortical areas converge with inputs from the thalamic intralaminar nuclei, dopaminergic inputs from the substantia nigra pars compacta, and serotoninergic inputs from the dorsal raphe nucleus. Connections arising from the limbic cortex and hippocampus are formed in a third structure, the nucleus accumbens, (Wilson; Basal Ganglia, 330)

Three input structures of the basal ganglia (caudate nucleus, putamen, nucleus accumbens), (Wilson; Basal Ganglia, 331)

Input fibers to the neostriatum arise primarily from the cerebral cortex, the intralaminar nuclei of the thalamus, the dopaminergic neurons of the substantia nigra (pars compacta), the serotoninergic neurons of the dorsal raphe nucleus, and the basolateral nucleus of the amygdala. Less numerous inputs also arise from the external segment of the globus pallidus and from the substantia nigra, pars reticulata, (Wilson; Basal Ganglia, 332)

The neostriatum is unusual in that the principal neurons, as well as many of the interneurons, are inhibitory. The principal neuron of the globus pallidus and substantia nigra is also inhibitory. Excitatory influences in the basal ganglia arise mostly from incoming fibers, (Wilson; Basal Ganglia, 345)

Neostriatal spiny cells fire very rarely and in episodes that last for only about 0.1 to 3 sec, (Wilson; Basal Ganglia, 345)

Cells in the globus pallidus and substantia nigra fire tonically at very high rates. Their tonic firing produces a constant inhibition of neurons in the thalamus and superior colliculus. , (Wilson; Basal Ganglia, 346)

Firing of spiny neostriatal neurons can cause a transient pause in tonic inhibition, releasing thalamic and superior colliculus neurons to respond to excitatory inputs that would otherwise be subthreshold, (Wilson; Basal Ganglia, 347)

The neostriatum acts to disinhibit neurons in the thalamus and superior colliculus; interneurons of the neostriatum help regulate the duration, strength, and spatial pattern of the disinhibition, (Wilson; Basal Ganglia, 347)

Cells in globus pallidus and in substantia nigra pars reticulata have very high rates of tonic activity. Fire rhythmically at a rate determined by membrane characteristics, (Wilson; Basal Ganglia, 373)

Inhibition exerted by (usually silent) neostriatal spiny neurons during their brief episodes of friring causes a momentary decrease in the rate of the tonic firing. , (Wilson; Basal Ganglia, 373)

Fast-firing cells of the globus pallidus and substantia nigra are GABAergic neurons, which exert a tonic inhibition on the target cells of the thalamus and superior colliculus, (Wilson; Basal Ganglia, 373)

The overall functionality of the basal ganglia and their interconnections provide a Jack-in-the-Box, rapid response functionality of stereotype programs for the motor cortex.

Overall, excitation of neostriatal spiny neurons leads to a disinhibition of the otherwise suppressed activity of neurons in the thalamus and superior colliculus, (Wilson; Basal Ganglia, 373)

Modality-specific thalamic nuclei share the following characteristics: (1) receive direct inputs from long ascending sensory  tracts or process information from basal ganglia, cerebellum, or the limbic system; (2) have reciprocal connections with well-defined cortical areas. (Afifi; Functional Neuroanatomy, 251)

Globus pallidus fibers project mainly on the ventral anterior  nucleus of the thalamus.  Collaterals of this projection reach the intralaminar nuclei. (Afifi; Functional Neuroanatomy, 247)

Cortical fibers to the intralaminar nuclei of the thalamus arise primarily from the motor and premotor areas. (Afifi; Functional Neuroanatomy, 247)

In contrast to other thalamic nuclei, connections between the intralamina nuclei and cerebral cortex are not reciprocal. (Afifi; Functional Neuroanatomy, 247)

Music and Basal Ganglia

Something may start randomly -- a tic, for example, bursting out of overexcited basal ganglia. (Sacks; Musicophilia, 86)

Fragmentary musical patterns may be emitted or released from the basal ganglia as raw music, without any emotional coloring or associations. (Sacks; Musicophilia, 88)

 

Excerpts from science experts

Basal ganglia are a set of huge nuclei in the depths of the forebrain that contain a vast number of neurons and that have evolved in parallel with the thalamocortical system. The long, one-way, parallel loops of the basal ganglia have the architecture to implement a variety of independent unconscious neural routines. They are triggered by the dynamic core at specific "ports out," do their job rapidly and efficiently, and then return the results to the core at specific "ports in." (Edelman; Universe of Consciousness, 184-185)

Basal ganglia participate in the development and expression of sequential motor acts; neurons in the basal ganglia fire selectively in relation to specific learned motor sequences. The type of connectivity typical of basal ganglia and similar loops (functionally insulated and connected to the dynamic core only at ports out and ports in) may be the reason such routines are unconscious. (Edelman; Universe of Consciousness, 185-186)

A trip in a single loop through the basal ganglia may take up to 100-150 msec. (Edelman; Universe of Consciousness, 186)

In addition to automatic motor routines, there are a large number of cognitive routines having to do with speaking, thinking, planning, etc. that may be unconscious. (Edelman; Universe of Consciousness, 186)

The enormous associative capabilities of the dynamic core are ideal to link or hierarchically organize a series of preexisting unconscious routines into a particular sequence. Pianist deliberately links separate arpeggio passages. (Edelman; Universe of Consciousness, 187)

The basal ganglia influences our conscious motor actions: from basal ganglia to thalamus to motor cortex.  (Edelman)  Edelman also proposes that our thoughts may also be influenced by the sub-cortical basal ganglia.  For one thing, the striatum, the first input level of the basal ganglia, has reciprocal connections with many of the cortical areas that give this first input to the basal ganglia.  Perhaps this increases activation of these cortical areas, which might be experienced as heightened environmental perception (posterior lobe), memory recall (temporal lobe), generalized environmental mapping and calculations (parietal lobe), and goal-directed intentionality (frontal lobes). (http://biosistemica.org/basal_ganglia.htm)

 It is also possible that the thalamic patterns, created by the basal ganglia output (from the substantia nigra and globus pallidus), can also influence cortical patterns outside of the motor cortex.  Thus, our thinking and other aspects of our mental life, once again, may be influenced by the sub-cortical basal ganglia.  For example, it is possible that the sequencing patterns of the basal ganglia motor routine can then return to the cortex, via the thalamus, to create sequencing of thoughts, both verbal thoughts and non-verbal thoughts. 

 

Science 23 November 2007: Vol. 318. no. 5854, pp. 1309 - 1312

Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism

Michael J. Frank,1 Johan Samanta,2,3 Ahmed A. Moustafa,1 Scott J. Sherman3

1 Department of Psychology and Program in Neuroscience, University of Arizona, Tucson, AZ 85721, USA.
2 Banner Good Samaritan Medical Center, Phoenix, AZ 85004, USA.
3 Department of Neurology, University of Arizona, Tucson, AZ 85724, USA.

Deep brain stimulation (DBS) of the subthalamic nucleus markedly improves the motor symptoms of Parkinson's disease, but causes cognitive side effects such as impulsivity. We showed that DBS selectively interferes with the normal ability to slow down when faced with decision conflict. While on DBS, patients actually sped up their decisions under high-conflict conditions. This form of impulsivity was not affected by dopaminergic medication status. Instead, medication impaired patients' ability to learn from negative decision outcomes. These findings implicate independent mechanisms leading to impulsivity in treated Parkinson's patients and were predicted by a single neurocomputational model of the basal ganglia.

 

 

Basal Ganglia (Koch; Quest for Consciousness, 226)

Basal ganglia of fish (Changeux; Neuronal Man, 43)

Succession, planning, and choice; the Basal Ganglia (Edelman; Remembered Present, 133)

Main anatomical connections of the basal ganglia and their relation to the cerebral cortex. - (diagram) (Edelman; Remembered Present, 135)

Motor components of the basal ganglia - (diagram)  (Purves, Neuroscience, 418)

Nuclear masses of the basal ganglia: caudate, putamen, globus pallidus. (Zeman; Consciousness, 61)

Basal ganglia - large and functionally diverse set of nuclei: caudate, putamen, globus pallidus, substantia nigra, subthalamic nucleus in the ventral thalamus. Certain basal ganglia components are required to initiate a movement and to terminate a movement. (Purves, Neuroscience, 418)

 Motor components of the basal ganglia make a subcortical loop that links most areas of the cortex with upper motor neurons in the primary and premotor cortex and in the brainstem. Caudate and putamen of the corpus striatum comprise the input zone of the basal ganglia. Large dendritic trees of the striatum allow them to integrate inputs from a variety of cortical, thalamic, and brainstem structures. Globus pallidus and substantia nigra pars reticulata are the main sources of output from the basal ganglia complex. (Purves, Neuroscience, 418)

 Nearly all regions of the neocortex project directly to the striatum, making the cerebral cortex the source of the largest input to the basal ganglia, by far. The only cortical areas that do not project to the striatum are the primary visual and primary auditory cortices. (Purves, Neuroscience, 418)

Of the cortical areas that innervate the striatum, the heaviest projections are from association areas in the frontal and parietal lobes, but substantial contributions also arise from the temporal, insular, and cingulate cortices. Association cortices receive inputs from a number of primary and secondary sensory cortices and associated thalamic nuclei. (Purves, Neuroscience, 418)

The fact that different cortical areas project to different regions of the striatum implies that the corticostriatal pathway consists of multiple parallel pathways serving different functions. Corpus striatum is functionally subdivided according to its inputs. Visual and somatic sensory cortical projections are topographically mapped within different regions of the putamen. Rostrocaudal bands within the striatum; functional units concerned with the movement of particular body parts. Functionally distinct pathways project parallel from the cortex to the striatum. (Purves, Neuroscience, 417-19)

Motor components of the basal ganglia - (diagram) (Purves, Neuroscience, 418)

Anatomical organization of inputs to the basal ganglia. - (diagram) (Purves, Neuroscience, 419)

Neurons and circuits of the basal ganglia - (diagram) (Purves, Neuroscience, 420)

Functional organization of outputs from the basal ganglia - (diagram) (Purves, Neuroscience, 422)

Basal ganglia loops and non-motor brain functions - (diagram) (Purves, Neuroscience, 432)

 

 

Return to — Movement Control

Return to — Fixed Action Patterns (FAPs)

Link to — Consciousness Subject Outline

Further discussion — Covington Theory of Consciousness