| |
Abstract:
Much of our normal behavior depends on learning how to
perform entire action sequences so smoothly that we carry them out
almost without conscious effort. This type of learning, known as
procedural or habit learning, is critical for maximizing cognitive
function. We depend on habits to free us to think and plan and to
react to novel events in the environment. Clinical and experimental
evidence suggests that our ability to acquire habits depends on the
basal ganglia, deep forebrain structures that are interconnected
with the frontal cortex in a series of loop circuits. Almost
nothing is yet known, however, about the type of neural processing
that lets us transform behaviors into habits. Nor do we understand
neural activity that allows us to perform complex acts
automatically once habits are formed. Our laboratory is focusing on
these two issues.
In rats, we are recording chronically from the striatum with
multiple tetrodes as the animals undergo training on a T-maze. We
find that large and widely distributed changes in neuronal activity
patterns occur in the sensorimotor striatum during behavioral
acquisition, culminating in task-related activity emphasizing the
beginning and the end of the automatized procedure. These new
ensemble patterns remain stable over weeks of subsequent
performance of the same task, and are accompanied by increases in
temporal coordination of spike activity. These results suggest that
a dynamic reorganization of population activity of striatal neurons
occurs as habit learning proceeds.
In monkeys, we are recording the patterns of neuronal activity
in frontal cortex and striatum as monkeys perform sequential
saccade tasks under conditions that favor either an attentive,
reactive mode of performance or an increasing automization of the
saccade performance. We are finding striking modulations of firing
frequency of supplementary eye field (SEF) neurons as the monkeys
switch from the reactive to the semi-automatic mode of saccade
performance. Initial recordings in the striatum of these monkeys
suggest that mode-specific modulation patterns occur there as well.
These experiments suggest that cortico-basal ganglia loop circuits
carry signals reflecting the stepwise release of performance from
reactive, attentional demands as performance becomes
increasingly.
|
