Interneurons descending from the cricket cephalic ganglia that discharge in the pattern of two motor rhythms

Summary

• 1. When male field crickets (Gryllus campestris L.) sing, abdominal respiration is usually synchronized with the chirps of the calling song. These experiments were designed to find a neuronal correlate of this synchronization.

  Animals with freely moving wings and abdomen are caused to produce normal song by brain lesions, during which the activity of single fibers in the cervical connectives is recorded extracellularly together with the myograms of the wing muscles and the expiratory abdominal flank muscles.

• 2. In each of three animals a descending neuronal spike pattern was found (I, II, III, respectively) in which bursts of impulses alternate with the chirps and the corresponding abdominal ventilatory activity (AVA). In silent males the bursts alternate with the AVAs and other abdominal movements.

• 3. The beginning of the neuronal burst is correlated with the end of the preceding chirp, no matter how long it is, and the end is correlated with the onset of the following chirp. The relationship to the chirp-coupled AVA is less clear-cut.

• 4. The muscle potentials in the chirp-coupled AVA are grouped so as to resemble the syllable pattern (animal I). Between these groups increasing numbers of neuronal impulses appear toward the end of the chirp. When the chirp is shifted with respect to the AVA, the spikes continue to follow the syllable rhythm.

• 5. A relation between Pattern I and the AVA becomes evident in the case of AVAs lasting through two chirps. The neuron fires more rarely during such AVAs than it does between AVAs coupled to a single chirp.

• 6. In silent males the neuronal burst both ends and begins later with respect to the AVA, and the discharge rate is lower.

• 7. After transection of all nervous connections to thorax and abdomen Patterns I and II are irreversibly altered. That is, the correlation of the neuronal pattern with the motor patterns must require ascending inputs from these regions. During singing these inputs would have to be correlated primarily with the rhythm of stridulation, whereas in the silent phase they would be correlated with the activity rhythm of the abdominal dorsoventral muscles alone.