What observations have aided the understanding of the motor cortex?

Sanjay Manohar, Cambridge 2001

Historic

                1870 Fritz & Hitzig

                                stimulation of frontal cortex of anaesthetised dog produced contralateral movement

                1900s Ferrier & Sherrington

                                Electrical stimulation shows contralateral precentral gyrus has lowest threshold for movement

                1920-1930 AW Campbell

                                comparative neurohistology shows motor cortex resides in Brodmann area 4

                Betz

                                proposed giant pyramidal cells project to LCST

                Stroke patients have contralateral impairment

M1 = Area 4 = precentral gyrus

                doctrine of one pyramidal cell => one motor neurone pool

                Penfield 1950

                                electrical cortex stimulation in epileptics yields motor homunculus

                Georgopoulos 19??

                                population vector coding for direction of movement

                cortical plasticity

                                Donoghue & Sanes: denervation in mice causes alteration of homunculus

                                fMRI in stroke patients shows alteration of map.

                                immediate change in cortical function (seconds)

Area 6 (both PMA and SMA)

                2 somatotopic maps

                Penfield

                                More complex movements: multiple muscle groups involved

                Roland

                                PET during random finger movement, memorised finger movement and mental rehearsal of movement

                                shows activity in M1, M1+Area 6 and Area 6 only, respectively

                                                => role in planning

SMA

                Evarts

                                activity 1 second prior to movement

                                bilateral representation of movements

                Lesions in monkeys and humans

                                bimanual deficit (buttoning/clapping)

                Anatomically

                                i) BG, Limbic system, PFC connections

                                o)

PMA

                1982 Weinrich & Wise

                                movement direction-specific (not stimulus-specific) response in cue-stimulus interval

                                                => representation of motor plan

                Kuypers

                                monkey lesions in PMA impair:

                                                shaping hand for target based on vision

                                                accounting for obstacles when reaching for food

                Anatomically

                                i) CBM, parietal cortex

                                o) medial tracts eg reticulospinal to proximal motor units