THE `PATH' THEORY OF CORTICAL FUNCTION*

THERE have been few general theories to accouint foI the f11nctioning of tlhe centra,l nervous system, buit there has becn one which, although it has niever been put forwar(d with any definite evidence, inevert-heless has gradually grown uintil it remains practicallyT the only theory in the field. 1. refer to the ' path ' theory, which states, roughly, that the fiunctions of the central nervous systemn are controlled by chains of neurons laid down as a path so as to conduct the impulse to its appropriate end-organ: that the paths a11re strictly constant, tllus accounting for the fact that the reflexes and reactions are largely constant: that learning consists of the openinig uip of new palths and that memory cons;ists of the retraversing of some old path by another impullse. But it is beginning to become apparent that the theory is in need of a thorou1gh overhaul, especially as it has never been clearly stated but tends to lie in tlhe background, emerging to explain some convenient fact yet not being questionled when facts appear which it is powerless to explain. It appears either explicitly or implicitlv in neurology, in physiology, and particularlIy in iny work which attempts to deal with phy siologi-cal psychology : and, curiously eniough, it is particularly in the latter that it breaks (lowni. It will be shown tlhiat there aire certaiin facts which are iniconmpatible with this theory; but first it is a<s well to examine its beginnings andl its development ' since this throws s,ome light on its present position. Galen, aboIut A.D. 190, first showe(d that an excise(d muscle may be made to twitch by pinching the nierve. He foundl that pinching the nerve at any, point of its course resulted in contrcaction, anid tha,t (livision of the nerve between the point of application of the stimulus and the nmuscle prevented contraction. Here, theni, was the first ' path ' theory, a theory which was obviouisly juistified by the facts. It wcts assumed that sorimething passed from the point of stimulaltion to the muscle and it w$as fouind that, given the state of the path, oIne could pre(lict whetlher, or not the muscle wouild contract. From this point there was a gap, buit by 1800 the grosser anatomy of the neivous system was well known, though practicallyv nothinig was known of its plhysiology. In 1811, Bell 2 mlade his fuindanmental discovery of the functions