EFFECTS OF CHANGES IN CENTRAL AND PERIPHERAL CONDITIONS ON ORGANIZATION OF COURTSHIP SONG IN GRASSHOPPER GOMPHOCERIPPUS REFUS L

During courtship the male grasshopper performs a sequence of movements mainly with the head and its appendages and the hindlegs. This behaviour can be released by optical, acoustical and tactile stimuli, but the performance of the movements does not seem to be controlled via visual or acoustic feed-back (Table 1). However, it is possible to interrupt the sequence by means of visual stimuli, leading to optomotor responses, but only during the phase of slow and not during fast head movements (Table 2). Extracellular recordings from muscles in the freely moving animal, following the operations listed below, indicate that courtship is determined predominantly by a programme laid down in the central nervous system. Peripheral control does, however, influence details of the whole pattern. a) The temporal sequence of muscle potentials is not changed by amputation or fixation of the hindlegs, but the activity of the individual motor unit may decrease (Figs. 1-4). b) If the hind legs are loaded, no increase in the activity of the muscles could be found (except in the coxal abductor) and heavy loading may even lead to a decrease (Fig. 5). c) Hind legs connected together mechanically do not alter the activity in the homologous muscles from the normal out-of-phase pattern to synchronous discharge (Fig. 6). d) If the head is fixed to the prothorax, the activity of the head moving muscles as well as their co-ordination with the leg muscles remains unchanged (Fig. 7), but the frequency of head oscillations is lowered at the beginning of a courtship unit. As soon as the pterothorax is also fixed to the prothorax and the head, no courtship song appears (Table 4). The central nervous mechanisms involved in the control of courtship seem to be arranged in a hierarchical manner. The sequence remains unchanged when only connectives on one side are cut between the head and the thoracic ganglia; stridulation stops, however, after severing both connectives anterior to the metathoracic ganglion, but the movements of the head and its appendages have been found normal (Figs. 8, 9). Rhythmical movements of the hindlegs can also be released by small lesions and focal electrical stimulation in the brain (Fig. 11, Table 6). © 1969 Springer-Verlag.