Motor programs of spontaneous and visually guided saccades in macaque monkey: an electrophysiological approach

The discharge activity of 37 burst neurons in the paramedian pontine reticular formation and the saccades performed in the dark (spontaneous saccades) and between visual targets (attentive visually guided) were recorded in two macaque monkeys. Forty-five % of spontaneous saccades showed more than one maximum of velocity (irregular velocity profiles), while visually guided saccades were always characterized by a single maximum of velocity (regular velocity profiles). The discharge pattern of each burst neuron (short lead neuron) was different according to the saccade velocity profile. We observed a clear inhibition within the burst neuron discharge for irregular velocity profiles, thus giving rise to multiple maxima of discharge frequency, and to a clearly interrupted saccade. The same neuron showed only one maximum of discharge frequency for regular saccades. Then the hypothesis of two different neural networks generating the different motor programs of spontaneous and attentive visual guided saccades is put forward and discussed.