PSYC 427 Lecture Notes - Lecture 11: Premotor Cortex, Prefrontal Cortex, Stretch Reflex

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PSYC 427 LECTURE 11
There is short-term sensory memory for events within the motor cortex.
Decision-making about magnitude of sensory stimuli occurs in cortical motor areas
This makes you question what the motor cortex is really responsible for
However, it is hypothesized that there is local memory more widespread than just within the motor cortex
LONG LATENCY STRETCH REFLEX
EMG from muscle that is ipsilateral to the stretch has two peaks:
1. M1: short latency (monosynaptic stretch reflex) lasting 10-15ms
2. M2: long latency (transcortical reflex) that begins shortly after M1
ROMO ET AL: SENSORY DECISION MAKING IN VENTRAL PREMOTOR CORTEX (F5)
Panel A: sequence of events
1. Mechanical probe is lowered (PD)
2. Monkey places free hand on key (KD)
3. Probe oscillates vertically at baseline stimulus frequency
A vibratory stimulus, comparable to a flutte, is lowered on the fingertip (low frequency)
4. After a delay, a second stimulus is delivered at comparison frequency
5. Monkey releases key (KU) and responds (PB) to indicate whether comparison is higher or lower than baseline
Panels B-D: stimulus sets used during recordings
Different combinations of base and comparison frequency used
Details are not important
The frequencies are manipulated in a systematic fashion to maintain a constant difference
o Interested in neural activity that codes the first stimuli, second stimuli and the difference between
Panel E: picture of brain surface
Black circle: site of recordings in VPC (area F5)
Abbreviations: AS = arcuate sulcus; CS = central sulcus; PS = principal sulcus
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F1 in the macaque corresponds to the primary motor cortex (area 4, M1) in humans
F4 and F5 in the macaque corresponds to ventral premotor cortex (area 6, PMv) in humans
Remember that sensory decision making occurs in F5
F3 in the macaque corresponds to supplementary motor area (area 6, SMA proper) in humans
Area 9/46V (ventrolateral prefrontal cortex) is located under the principal sulcus
It is prefrontal yet its inputs and outputs are somatic
It is active during somatosensory decision making
The brain holds information about the first stimulus in memory in order to compare it with the second stimulus.
Above are 4 different neurons, all from the ventrolateral prefrontal cortex.
Horizontal axis: time
Each row has labels with the combination frequency used
o For example: the first row is labeled 26:34, meaning the first stimulus was 26Hz and the second 34Hz.
Each dot is an individual action potential
Grey bars: onset of first and second stimuli
Note that the first five labels are written in black, indicating that the vibratory frequency was higher for the second stimulus, and the last 5 written in grey, indicating
that the vibratory frequency was higher for the first stimulus.
In general, there is not much activity before the first stimulus- or even between the stimuli. However, for both the first and second stimuli, there is significant
neuronal discharge.
Panel A: from the lowest trial (10:18) to the upper trial (26:34), the discharge frequency increases
As stimulus frequency goes up, the firing rate goes up
Thus, the neuron is coding the frequency of the stimulus
Panel D: there is no discharge during presentation of stimuli. However, starting from the top row to half way down (10:18), there is gradual increase in firing rate as
you get further into the delay period (time between the two stimuli).
Firing during delay period increases as a function of the frequency of the first stimulus
Thus, this neuron is holding onto info about the first stimuli. It is a pure memory cell!
Panel G: this neuron responds to the first stimulus; as the frequency of the first stimulus decreases, firing rate increases.
During the comparison period (f2), after a short delay, the neuron begins firing vigorously if the frequency of the second stimulus is higher than the first.
However, the neuron shuts off if the frequency of the second stimulus is lower than the first stimulus
Thus, this neuron is involved in the comparison process, firing only when its preferential difference between stimuli is present (F2>F1)
Panel J: this neuron has a selective response during the comparison period (f2); it shuts off when the second stimulus has a higher frequency and continues firing if it
has a lower frequency. Additionally, it is active during the delay period.
In conclusion, neurons all have the capacity to encode information about the first stimulus, which is maintained in working memory during the delay period. This
memory enables selective responding. In other words, different neurons have different responses to the comparison stimulus, depending on the property of the
neuron.
The activity of ventral premotor cortex neurons reflects current and remembered sensory inputs, their comparison and motor commands expressing the result;
that is, the entire processing cascade linking the evaluation of sensory stimuli with a motor report.
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Document Summary

There is short-term sensory memory for events within the motor cortex. Decision-making about magnitude of sensory stimuli occurs in cortical motor areas. This makes you question what the motor cortex is really responsible for. However, it is hypothesized that there is local memory more widespread than just within the motor cortex. Emg from muscle that is ipsilateral to the stretch has two peaks: m1: short latency (monosynaptic stretch reflex) lasting 10-15ms, m2: long latency (transcortical reflex) that begins shortly after m1. Romo et al: sensory decision making in ventral premotor cortex (f5) Panel a: sequence of events: mechanical probe is lowered (pd, monkey places free hand on key (kd) After a delay, a second stimulus is delivered at comparison frequency. A vibratory stimulus, comparable to a (cid:862)flutte(cid:396)(cid:863), is lowered on the fingertip (low frequency: monkey releases key (ku) and responds (pb) to indicate whether comparison is higher or lower than baseline. Different combinations of base and comparison frequency used.

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