| Houk,
et.al.; Models of Information Processing in the Basal
Ganglia |
|
|
| Book |
Page |
|
Topic |
|
|
| 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.
|
|
0 |
| 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 |
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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. |
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0 |
| Jackson
& Houghton; Basal Ganglia Model |
341 |
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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. |
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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. |
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0 |
| Jackson
& Houghton; Basal Ganglia Model |
342 |
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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. |
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| Jackson
& Houghton; Basal Ganglia Model |
342 |
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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. |
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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. |
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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. |
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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. |
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0 |
| Graybiel;
Adaptive Neural Networks in Basal Ganglia |
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