PSYC 427 Lecture Notes - Lecture 7: Pyramidal Tracts, Antidromic, Central Sulcus
14 May 2018
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PSYC 427 – LECTURE 7
Pyramidal tract neurons (PTNs): output cells in layer V
SELECTION CRITERIA FOR PTNS
• Weak intracortical microstimulation could evoke finger movements
• Antidromic activation at short latency by medullary pyramidal tract stimulation
o Antidromic activation: used to see if recorded neuron in one part of the cortex projects to another region
• Discharge clearly modulated in relation to voluntary finger movements
• Located in anterior bank of central sulcus
Additional collision test: is nullification possible?
• Whether or not the antidromic signal is eliminated by stimulating the cortex
• Confirms that what is being stimulated is an output cell, not an interneuron
Eats deostated…
• Activity of pyramidal tract neurons precedes onset of EMG activity of wrist flexion/extension movements
• Activity is related to the force, rather than direction of movement.
The okes’ task as to ait ith its fige o a ke ad elease the ke i espose to a light
• Above is a spike train, or series of action potentials as a function of time
• Horizontal trace is when the finger was raised and key released
The signal was related to the initiation of movement, rather than the visual stimulus
• Timing of motor cortex activity was closely correlated with timing of muscle activity
• Left: all records are aligned with the onset of visual stimulus
Key finding: pyramidal tract activity (M1 action potentials) was found to precede EMG in agonist muscles by as much as 100ms.
• Demonstrates planning of movement and lack of reliance on feedback
x-axis: time; y-axis: proportion of cells
Above is the frequency distribution of the onset of activity in pre-and post-central neurons in relation to the movement onset (R)
• The pre-central units (motor cortex) are active 50-60ms before movement starts
o Remains active during movement
• The post-central units (somatosensory cortex) discharge almost entirely after movement onset
A high proportion of pyramidal tract neurons show changes in activity related to direction of intended movement
• Cells have a preferred direction of movement
1. Monkey holds robot arm and is given visual warning signal, which species the upcoming movement direction
2. A Go sigal is applied the robot several seconds later
• Two possible instructions: push or pull
• Triggered by sensory input, or displacement of the limb
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1. Moke gasps od ad holds it i the ete hold zoe: midway between push and pull
• Holding period varied unpredictably from 2-5s
2. Red or green lamp came on
• Red: instruction to pull when handle was subsequently perturbed
• Green: instruction to push when handle was subsequently perturbed
3. Either of the two possible instructions (push or pull) was followed by either of the two possible directions of perturbation (push or pull)
Bottom: Discharge raster
• Each dot represents an action potential
• Each row is a single trial
• Dark line in the middle is when the visual info was given (instruction to push or pull)
• Instantaneous discharge rate of a PTN for 1s before and 1s after appearance of the pull and push signal
Top: frequency distribution
• Bins represent summation of activity in successive 40ms periods
• Height of the line represents number of action potentials recorded within each band
Pogessiel oe the 1s afte the isual sigal, thee is oe ad oe atiit i the ell fo the oeet dietio pefeed the PTN
• O the ota, atiit deeases fo the opposite, less pefeed dietio of oeet
An instruction as to a forthcoming movement leads to anticipatory activity in motor cortex neurons, even though there is no muscular response while awaiting the
signal (red or green). These instruction-related changes in motor cortex activity persist while the monkey waits.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Pyramidal tract neurons (ptns): output cells in layer v. Selection criteria for ptns: weak intracortical microstimulation could evoke finger movements. Antidromic activation at short latency by medullary pyramidal tract stimulation. Antidromic activation: used to see if recorded neuron in one part of the cortex projects to another region. Discharge clearly modulated in relation to voluntary finger movements. Additional collision test: is nullification possible: whether or not the antidromic signal is eliminated by stimulating the cortex. Confirms that what is being stimulated is an output cell, not an interneuron. Activity of pyramidal tract neurons precedes onset of emg activity of wrist flexion/extension movements. Activity is related to the force, rather than direction of movement. The (cid:373)o(cid:374)ke(cid:455)s" task (cid:449)as to (cid:449)ait (cid:449)ith its fi(cid:374)ge(cid:396) o(cid:374) a ke(cid:455) a(cid:374)d (cid:396)elease the ke(cid:455) i(cid:374) (cid:396)espo(cid:374)se to a light. Above is a spike train, or series of action potentials as a function of time. Horizontal trace is when the finger was raised and key released.
