Fig. 6. Extracellular recording from a single trigeminal ganglion unit in the unattached and attached state. The instantaneous frequency plot and interspike interval (ISI) histogram accompanying each trace were constructed from a single unit discriminated on the basis of spike shape. (A) Spontaneous activity in the unattached state. (B) In the weight-attached state, firing rate is increased. For each recording the accompanying ISI histogram is unimodal and skewed. The coefficient of variation (CV=S.D./mean ISI, measure of regularity) values show firing to be irregular. Firing rate over the 5 min period (total number of spikes/total time period) is also shown.