Motor Cortex Flashcards
M1 neurons fire how long before the onset of a movement? What does this mean?
5-100ms. Means involved in relaying commands to alpha MNs.
Why in humans do large M1 lesions have less potential for recovery than in monkeys?
Increased importance of descending signals from M1 onto spinal interneuronal circuits and spinal motor neurons. CST more direct connections in ventral horn in humans than in monkeys.
M1 does what ?
Generates motor commands which control spinal activity, including essential information necessary to select the location, timing and magnitude of muscle activity.
How are motor commands spatially specific?
Somatotopic M1. Different neurons project to different spinal cord levels.
Stimulation of what area of M1 leads to movements of the contralateral leg?
Anterior paracentral lobule.
As stimulating electrode (M1) moves X to X, movements are elicited progressively from the …
What does this explain?
Dorsomedial to contralateral, progressively from the torso, arms, face.
Jacksonian march seizures, simple partial seizure spreads from distal part of limb towards face. Reflects spread of electrical activity along M1.
Evidence for M1 neurons encoding force?
Fetz and Cheney (1980). Tonic firing rates increased with amplitude of torque across single joint.
Evidence for directional tuning in M1?
Georgopoulos et al (1982). Found cell that fired maximally when hand moved 180, moderately 90, none 0.
Evidence for speed tuning in M1?
Targeted movements follow bell-shaped curve. FR of some M1 neurons in monkeys correlate with profile.
Readiness potential occurs how long before movement onset? (Observed in PMA and SMA).
0.8 to 1 second.
SMA active for what sort of movement? Give 2 examples.
Internally generated. Deciding to stand up or playing a memorised piano piece.
What allows SMA to be involved in the sort of movements it is?
Receives input from PFC, which is responsible for decision making and intention formation.
Allows SMA to plan and initiate movements based on internal goals.
SMA involved (mote specifically) in what (2)? How do we know?
Movement sequencing.
Lesions challenges. Also finger tapping no activation, sequence added active.
Bimanual co-ordination, tying shoelaces. Lesions cause deficits.
PMA is involved in what sort of movement? Give 2 examples.
Stimulus-driven movement. Obstacle avoidance, grasping.
Why is PMA able to be involved in the sort of movements it is?
Receives input from PPC (dorsal visual stream). Translates visual input into grasping motor plans specific to object’s location and shape. Affordances.
How do we know PMA involved in externally-generated movements?
Monkey feeds food behind transparent barrier, readily reaches around.
Large PMC lesion, persistently reaches toward, striking barrier.
What study showed that there is not a strict dichotomy between SMA and PMA activity?
Mushiake et al (1991). More SMA (65%) pref. active during IT, more PMA (64%) during VT.
What is the function of the PPC? Enables what? How?
Sensorimotor integration, combines somatosensory and visual information to help plan movements.
Enables co-ordination of body movement according to visual cues.
Takes information from retinotopic space to egocentric space (somatotopy). Creating an internal map of body in relation to VF.
How do we know the PPC integrates across touch and vision.
Damage leads to visuospatial neglect and somatic neglect.
