gating of movement-related neural activity ?

Andrew_R._Mitz arm at helix
Sun Aug 20 21:12:34 EST 1995


MGLinWS (mglinws at aol.com) wrote:
: Previous studies have established that the neural representation of
: sensory activity is gated by the animal's motoric state.  Does anyone know
: of any studies that show that the neural representation of movement is
: gated by the animal's preparation to move ?  

: I have been studying neural activity in the striatum and frontal cortex of
: rats during reaction-time performance and have found that both preparatory
: and movement-related activity differ with the animal's reaction-time and
: with the length of the preparatory interval prior to the trigger stimulus.
: The movements made by the animal appear to be constant independent of the
: reaction-time and the length of the preparatory interval.  (This is based
: on a detailed analysis of video-tape. I am currently recording EMG
: activity together with neural activity to assess if the differences I see
: are due to different patterns of muscle activity.)

: As the striatum and frontal cortex are not primary motor structures, one
: might expect that neural activity in these structures may vary with the
: degree to which the animal is prepared to move (i.e., motor preparation,
: readiness, preparatory set).  I interpret my data as evidence for motor
: preparation gating the transmission of movement-related neural signals. 
: Moreover, these data suggest that a "movement-related" neuron is not
: necessarily responding to movement per se.

: I wonder if my observation is novel or if I have rediscovered an already
: obvious fact.  Any information will be greatly appreciated.
:  

The main problem here is that it is unclear if a rat has a premotor
cortex (PM).  Activity in monkey PM is often related to an upcoming movement,
independent of how the movement is cued or triggered (but only if the
cue or trigger is well-learned).  There are a number of papers on this
phenomenon.  Search for papers by S. P. Wise for reviews on PM.  
Basically, if a monkey knows what movement to make (i.e. receives
a cue signal) before it is permitted to make the movement (i.e. receives a
separate trigger signal), PM cells associated with that movement
are active just after the cue and shut down just after the
trigger.  (Actually, many PM neurons also fire during the movement).
Thus, within (certain parts of) PM the unit activity is in preparation
for an upcoming movement.  During a choice reaction-time task this PM 
activity would look "movement-related", since the cue signal and
the trigger signal are one and the same.  Note that preparatory
activity has also been observed in the supplementary motor area
SMA, an area that rats apparently do have.

There is lots more to the PM and SMA stories, but first, is this
the kind of information you are looking for?


--
------------------------------------------------------------------------
Andrew Mitz, Biomed. Eng., National Institutes | Opinions are mine alone 
of Health Animal Center, Poolesville, MD       | arm at helix.nih.gov       
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