Maps and Thresholds for the Sensorimotor Cortex of the Cat

This is the authors' abstract. We don't add key points for this paper.

Single cathodal square current pulses, optimum duration 15 msec., and strength 09 to 2-0 mA, have been applied to the cat's motor area.The lowest- threshold foci for flick movements of forelimb, hindlimb and face have been mapped in 25 experiments.There is no systematic difference between the thresh- holds of the different foci, but the forelimb focus had the lowest threshold in about half the experiments.Repetitive stimulation yields a range of movements not much greater than single-pulse stimulation.The regions of lowest threshold to single surface-negative shocks are not regularly associated with particular groupings of large pyramidal cells.Maps of the tactile receiving area are largely co-extensive with the motor maps in the same individuals.EXPERIMENTS on the motor cortex of the baboon [Liddell and Phillips, 1950, 1951] have shown that motor maps of two general types may be drawn, according to the characteristics of the electrical stimuli employed.Single rectangular pulses (optimum duration 5-0 msec.), at weakest effective strength, will only excite movements when applied to a focus in the arm area.Each shock causes a flick movement of thumb and index finger of the opposite side.This focus is enlarged if the shocks are strengthened a little, and a second focus in the leg area now becomes effective.It causes flicks of the opposite hallux, with or without other toes.Further strengthen- ing is needed for the uncovering, in the face area, of foci for angle of mouth and tongue.The map delineated by these stronger shocks consists finally of thumb-index, hallux and face areas which overlap extensively, covering a large part of the motor area.If the same shocks are increased in frequency, e.g. to 50 c/s, another and more familiar type of map, the classical motor map [e.g.Graham Brown and Sherrington, 1911], is obtained.On this map, narrower foci for a very rich variety of peripheral movements are portrayed.These narrower foci are not all equally excitable, and the differences in threshold between them are evident in experiments of two kinds.First, the threshold current is lower for certain foci: in macaque, for toes, thumb and mouth [Boynton and Hines, 1933], and fingers [Woolsey, Settlage, Meyer, Sencer, Hamuy and Travis, 1952]; in cat, for flexion of elbow, and in dog, for flexion of hind leg and ankle [Tower, 1928].Second, when current strength is adjusted so that a large number of foci become excitable, the lowest-threshold foci require shorter trains of shocks-or shorter summation periods (as defined by Cooper and Denny Brown [1927])-than the remaining foci [Liddell and Phillips, 1950].