PSYC 427 Lecture Notes - Lecture 18: Dentate Nucleus, Putamen, Muscimol
14 May 2018
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PSYC 427 – LECTURE 18
Neural activity in post-instruction period is indicative of preparatory or memory-related activity. To dissociate the direction of preparatory set (and limb movement)
from the task-related patterns of tonic and phasic muscular activation, some trials included application of a constant torque load that either opposed or assisted the
movements.
The task involved two movements
1. First movement chosen at random, after which the monkey returned to the center hold position (unknown)
• Cursor either on right or left is illuminated
• When illuminated, monkey moves to location of illuminated cursor then back to center
2. Second movement in the same direction as the first movement (known)
Unlike the first movement, the monkey knows where to move for the second movement. Thus, it is able to prepare in advance.
It was found that loads have no effect. Thus, the results are related to planning of movement in particular directions, not force or muscle activity.
Above is neural activity recorded from M1, SMA and putamen during a visuomotor step-tracking task
During this task, elbow movements were made both with and without prior information about the direction of upcoming movement
• Top 3 rows: extension movements
• Bottom 3 rows: flexion movements
• Aligned at movement onset
• Thick line: target (illumination) onset
Left panel: first movement (direction unknown)
• No difference in activity before onset of target
• Note that after the target comes on, there is no movement-related activity. Thus, this cell is not coding movement.
Right panel: second movement (direction known)
• SMA neuron shows preparatory activity during the delay period
• Note that activity is only in the extension direction (selectivity)
• Also, once movement begins, the neuron becomes inactive.
In all areas, preparatory activity was found to be independent of load
• Preparatory activity in M1 and SMA preceded activity in putamen.
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The M1 neuron shows both preparatory and movement-related activity.
Left: cell is active before movement onset
• Note that activity is only for extension movements (selectivity)
• No difference in activity depending on load (contrary to Evarts finding)
Right: there is more activity in the run-up period prior to extension movement (and less before flexion movement)
Thus, there is preparatory activity before making a known, preferred movement and suppression of activity before a known movement in direction opposite to the
preferred direction.
This M1 neuron shows preparatory activity but no movement-related activity (between target and movement onset)
• Active during preparation period for known flexion movements
• Inactive during preparation period for known extension movement
Thus, not all neurons are the same- even if they are found in the same area
• Variety of cell properties can be found within M1
This putamen neuron shows preparatory activity (but no movement-related activity)
• Lower overall discharge rate
• There is differential activity in post-instruction period: only for flexion movements
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Latency: onset time of recorded neuron relative to movement initiation
Majority of cells in the putamen have onset times after movement
• Later than SMA and M1 cells, majority of which have onset times before movement
Mink and Thach (1991) showed that pallidal neurons are not involved in movement initiation
• In this task, monkeys made movements to visual targets
• Above are single neuron recordings from GP penetrations in 5 different animals
The modal times of change for GPi were significantly later than those for forearm agonist muscle EMG
• GP is never active before movement initiaton
By contrast, the modal time of change for cerebellar dentate nucleus preceded that for wrist agonist muscle EMG
Thus, there is inconsistent coding of movement parameters by pallidal neurons.
• Onset is not systematically related to movement direction (or any other parameter)
Reaction time is normal following muscimol injection: reversible cooling of pallidum (inactivation); GABA receptor antagonist
• In other words, even if GP is removed from the circuit, reaction time is not affected.
GP output structures were studied to determine its role in movement.
• Bottom raster: activity in GP
o Solid bar in raster: 1) go-signal and 2) reaching of target location
• Middle: binned activity
• Line: movement onset
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Document Summary
Neural activity in post-instruction period is indicative of preparatory or memory-related activity. To dissociate the direction of preparatory set (and limb movement) from the task-related patterns of tonic and phasic muscular activation, some trials included application of a constant torque load that either opposed or assisted the movements. Cursor either on right or left is illuminated. First movement chosen at random, after which the monkey returned to the center hold position (unknown: when illuminated, monkey moves to location of illuminated cursor then back to center. Second movement in the same direction as the first movement (known) Unlike the first movement, the monkey knows where to move for the second movement. Thus, it is able to prepare in advance. It was found that loads have no effect. Thus, the results are related to planning of movement in particular directions, not force or muscle activity. Above is neural activity recorded from m1, sma and putamen during a visuomotor step-tracking task.
