CODING OF SOMATIC SENSORY INPUT BY VIBRISSAE NEURONS IN RATS TRIGEMINAL GANGLION

As part of a program to elucidate sensorimotor mechanisms involved in rat 'sniffing' behavior, the response characteristics of 616 single units in the trigeminal ganglion were studied in 52 anesthetized albino rat. The mystical vibrissae and surrounding facial regions were stimulated by delicate mechanical stimuli delivered either manually or by an electronically-controlled stimulator. Units which were activated by stimulation of vibrissae were always activated by deflection of one and only one vibrissa. Five categories of such 'vibrissae units' were identified. The units in each category were distinguished from those in other categories by directional sensitivity, velocity threshold, adaptation rate, and responsiveness to stimulus return. Sectioning of the trigeminal nerve root did not affect such receptive field and response characteristics of the units. Unit response patterns were also studied when vibrissae movements, characteristic of the awake exploring rat, were simulated by electrical stimulation of the facial motor nerve. These experiments show that when a rat encounters objects which deflect its mobile or stationary vibrissae, a relatively large population of first-order somatic sensory neurons is capable of coding the following aspects of mechanical stimuli: peripheral location, deflection direction, onset, termination, amplituded, velocity, duration, repetition rate, and temporal pattern. © 1969.