The Basal Ganglia for Cognitive Scientists

8/7/2019 The Basal Ganglia for Cognitive Scientists

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Basal Ganglia for CognitiveScientists

The primate basal ganglia: parallel andintegrative networks

(Haber, 2003)

Dopamine, Learning, and Production Rules:

The Basal Ganglia and the Flexible Control ofInformation Transfer in the Brain

(Stocco, Lebier & Anderson, 2009)


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BG for Cognitive Scientists

Anatomy and circuitry

Circuitry highlights

Parallel versus integrative networks

Cognitive function of the basal ganglia

Routing model of the basal ganglia

Routing and production rules


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Basal Ganglia: anatomy


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Basal Ganglia: anatomy


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Basal Ganglia: circuitry

Input

Striatum

Caudate

Putamen Subthalamic nucleus

Output (via the thalamus)

Globus Pallidus internal segment (GPi) Substantia Nigra pars reticulata (SNr)


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Basal Ganglia: circuitry


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Topographical connections

Direct and indirect pathways

The role of dopamine


Cognitive function of the basal ganglia Routing model of the basal ganglia

Comparison and implications of the model


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Topographical connections


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Direct & indirect pathways


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Role of dopamine


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Parallel vs integrative networks

Integrative networks

Two types of integrative circuits

Cognitive function of the basal ganglia Routing model of the basal ganglia



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Topographical connections suggest parallelprocessing of cortical information

BG are critical in mediating learning process byreinforcing new behavioral-guiding rules

Parallel processing does not explain learningand adaptability necessary in goal-directedbehavior


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1. Dendrites and axons crossing functionalboundaries

2. Convergence of terminals from functionallyadjacent fields onto progressively smaller BGstructures

3. Non-reciprocal connections betweenstructures that direct the 'flow of informationthrough the functional circuits


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Two types of integrative circuits

A striato-nigro-striatal network governed bydopamine from the SNr neurons in the midbrain

A thalamo-cortico-thalamic interface with anactive role for the thalamo-cortical connections


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Striato-nigro-striatal circuit


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Thalamo-cortico-thalamic circuit


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Nice, but where does cognition comes in?


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Topographical connections revisited


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BG and the procedural module

ACT-R claims a functional correspondencebetween the procedural module and theactivity of the basal ganglia

The procedural module executes operations inthe form ofconditionaction rules

A rule responds to specific contents of modulebuffers corresponding to representations held inthe cortex


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Routing model of the BG

Actions performed by the basal ganglia can bethought of as routing operations

Routing operations define which signals aretransferred between source regions to targetregions in the cortex


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Striatal neurons:

SN: striatonigral

direct pathway

represent source SP: striatopallidal

indirect pathway

represent non-targets

IN: interneurons

inhibit SN and SP

implement rules


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Interneurons implement rules

A rule is embedded in the incoming andoutgoing synapses of interneurons

Condition part of the rule are incoming

synapses encoding the cortical representationthat will trigger the neuron to fire

The action is encoded in the outgoing synapsesand activating SN or SP neurons

SN and SP neuron activation triggers thetransmission of information from the sourceregion of the cortex to the target region.


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Interneurons implement rules


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Topographical connections revisited

SN and SP are large sets of neurons with aratio of 1:10 to the represented neurons in thecortex

Both, cortical regions and theirprojections toother regions are encoded using these neurons

Apart from the compression theserepresentations remain stable through the

subsequent nuclei in the basal ganglia So these are parallel networks


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Direct & indirect pathways revisited

Input from indirect pathway is delayed withrespect to that from the direct pathway

Delay can be used as a memory for theprevious state

The SNr / GPi can compare the current

source regions with the previous destinationregions


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Role of dopamine revisited

When a region belongs to both, current sourceand previous destination, dopamine neurons inthe SN receive an extra boost of activation

These neurons project to the stratium In the stratium the extra dopamine modifies

the activation ofSN and SP projection neuronsand the interneurons

Thereby a compressed copy of the corticalrepresentation gets stored as constants in anencoded rule


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Production compilation in ACT-R

Merging two condition-action rules that fireconsecutively into a single-step rule

This will happen when an action from the first

rule suffices as a condition for the second one Actions of both rules will be encoded as the

result of the first and an assumed condition(constant)

This implements skill acquisition includingcognitive and motor skills


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Habbit Learning


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Habbit Learning


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Haber (2003) revisited

Output nuclei (SNr and GPi) project back tothe cortex through the thalamus

The router model does that by changing

cortico-cortical connections This might resemble processes in the thalamo-

cortico-thalamic interface

The model implements a dopamine governedstriato-nigro-striatal network with an intrinsicreward independent from the limbic system


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Parkinson revisited


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Parkinson revisited

Parkinson disease involves death of dopamine cellsin SNr

This can be modeled by simulating damage to theseunits by:

Increasing input to SN units in the stratium

Corresponding decrease in input to PN units

The router model predicts that Parkinson Diseaseaffects skill acquisition

Dysfunction of the routing mechanism is not limited tomotor skills


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Cognitive science of the BG

Merging the routing model of the basal gangliawith ACT-R allows to model impairment of skillacquisition by cognitive diseases

Models of specific tasks predict reaction times Activation of specific ACT-R modules can be

used to model BOLD responses in fMRI


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The Basal Ganglia for Cognitive Scientists

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