NEURAL ACTIVITY IN MECHANORECEPTIVE CUTANEOUS AFFERENTS: STIMULUS-RESPONSE RELATIONS, WEBER FUNCTIONS, AND INFORMATION TRANSMISSION

Abstract

A study has been made of the neural activity evoked in first-order mechanoreceptive fibers ending in Iggo corpuscles of the hairy skin of cats and monkeys by mechanical stimuli. After an early onset transient discharge the responses to stimuli of short duration (500 msec) continue in a highly periodic fashion during a period of time designated an early steady state. The S-R relation between skin indentation and the level of activity in this state is accurately described by a power function of the general form R = K.Sn, with exponents commonly less than one. Certain derived aspects of this relation were explored in an effort to correlate these physiological events with psychophysical findings in man. Weber functions were constructed which parallel that of man for tactile sensibility (which is not Weber''s law) on the assumption that the least discriminable increment in neural response is a constant, not a fractional, increase. S-R matrices were constructed and the information transmitted per stimulus calculated. With increase in stimulus uncertainty beyond 4-5 bits, a/ the information transmitted per stimulus leveled off at about 2.5 bits, a value comparable to that found for man for a number of sense continua.