Graded Potentials and Spiking in Single Units of the Oval Organ, a Mechanoreceptor in the Lobsterventilatory System Iii. Sensory Habituation to Repetitive Stimulation

When the oval organ is stimulated repetitively at frequencies imitating normal scaphognathite beating the responses of the three sensory afferents decline. The number of spikes per response diminishes, the firing rate declines and the latency of the first spike may increase. The term ‘sensory habituation’ is proposed to describe the decline in response of a primary sensory unit to a repetitive train of identical stimuli. The decline in spiking performance is shown to be due to some or all of these underlying changes: (a) a decline in the rate of rise of the graded potential, (b) a decline in amplitude of the graded potential, (c) a decline in the rate of growth of the active process leading to spike initiation and (d) a rise in spiking threshold. The graded potential undergoes less of a reduction than impulse generation. Tetrodotoxin-treated fibres show little habituation to stretch. Normal fibres habituate to repetitive pulses of depolarizing current. It is suggested that during regular quiet ventilation the analogue signal alone provides feedback. Any extraneous perturbation or change in scaphog nathite rhythm restores spiking.