The following article is now available at
http://www.cns.bu.edu/Profiles/Grossberg in PDF:
Brown, J.W., <http://cns-web.bu.edu/Profiles/Bullock.html>Bullock,
D., and <http://cns-web.bu.edu/Profiles/Grossberg/>Grossberg, S.
(2003). How laminar frontal cortex and basal ganglia circuits
interact to control planned and reactive saccades. Neural Networks,
in press.
How does the brain learn to balance between reactive and planned
behaviors? The basal ganglia and frontal cortex together allow
animals to learn planned behaviors that acquire rewards when
prepotent reactive behaviors are insufficient. This paper proposes a
new model, called TELOS, to explain how laminar circuitry of the
frontal cortex, exemplified by the frontal eye fields, interacts with
the basal ganglia, thalamus, superior colliculus, and inferotemporal
and parietal cortices to learn and perform reactive and planned eye
movements. The model is formulated as fourteen computational
hypotheses. These specify how strategy priming and action planning
(in cortical layers III, Va and VI) are dissociated from movement
execution (in layer Vb), how the basal ganglia help to choose among
and gate competing plans, and how a visual stimulus may serve either
as a movement target or as a discriminative cue to move elsewhere.
The direct, indirect and hyperdirect pathways through the basal
ganglia are shown to enable complex gating functions, including
deferred execution of selected plans, and switching among alternative
sensory-motor mappings. Notably, the model can learn and gate the use
of a What-to-Where transformation that enables spatially invariant
object representations to selectively excite spatially coded movement
plans. Model simulations show how dopaminergic reward and non-reward
signals guide monkeys to learn and perform saccadic eye movements in
the fixation, single saccade, overlap, gap, and delay (memory-guided)
saccade tasks. Model cell activation dynamics quantitatively simulate
seventeen established types of dynamics exhibited by corresponding
real cells during performance of these tasks.
Key Words: basal ganglia, frontal cortex, cortical layer, saccade,
gating, dopamine, reinforcement learning, action selection, planning,
Parkinson's disease
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