gating of movement-related neural activity ?

MGLinWS mglinws at
Wed Aug 23 19:36:00 EST 1995

arm at helix (Andrew_R._Mitz) wrote:

:You obviously have some specific task procedure in mind.  How does
:the start of a trial differ from the trigger stimulus in a RT task?

The task I use is analogous to a task used by Amalric and Koob (J.
Neurosci., 1987) to study reaction-time performance in the rat.  I use a
nose-poke operandum instead of a bar.

After each correct response, a light inside the operandum is turned on and
the rat begins each trial by placing his snout inside the operandum, thus
breaking a photobeam.  This behavior results in the nose-poke operandum
light turning off and initiates the preparatory interval (500-2000 msec). 
If the animal sustains the response over this interval, an auditory
trigger stimulus (tone) is presented for 200 msec.  The animal must
withdraw from the operandum within 600 msec to obtain a drop of water.

The start of each trial is distinct from the trigger stimulus as the
events are cued by different stimuli and are separated in time.

The goal of this design was to examine how the spike activity of neurons
that become active during the preparatory interval vary in relation to the
animal's reaction-time and as a function of the length of the preparatory
interval.  However, only a portion of the neurons fire in a preparatory
manner and others fire in relation to movement.  I noticed that both
"types" of cells varied in relation to the reaction-time and the length of
the preparatory interval.  The animal's movements did not vary in relation
to these factors (as determined from time measurements of video-tape of
the behavior during the neural activity).  

Therefore, I was prompted to ask: are the neurons that show differences
being differentially activated by their inputs as a function of the
reaction-time or the preparatory delay ?  The data suggest to me that a
process of motor readiness may arise in the corticostriatal pathways and
give rise to a differential expression of both preparatory and
movement-related activity in the frontal cortex (medial agranular area)
and dorsal striatum.

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