The influence of the auditory cortex on acoustically evoked cerebellar responses in the CF-FM bat, Rhinolophus pearsonic chinesis

Summary

• 1. Acoustically evoked responses of 284 neurons isolated from the cerebellar vermis, hemispheres and paraflocculus of Rhinolophus pearsonic chinesis were studied under free field acoustic stimulation conditions.

• 2. The BFs of these cerebellar auditory neurons ranged from 24 to 76 kHz but they mostly fall either between 48 and 64 kHz or between 65 and 76 kHz (Fig. 1). However, the BF distribution varies among vermal, hemispheric and parafloccular neurons (Fig. 2).

• 3. Threshold curves of cerebellar neurons are generally broad but those tuned to the frequency of the predominant CF component are extremely narrow (Fig. 3).

• 4. Response latencies of cerebellar neurons ranged from 2 to 48 ms suggesting multiple auditory cerebellar pathways. The latency distribution also varies among vermal, hemispheric and parafloccular neurons (Fig. 4, Table 1).

• 5. Although both the vermis and hemispheres contain a disproportionate number of 65–74 kHz neurons, the response latencies of those neurons isolated from the vermis are scattered over a wide range of 2.2–28 ms while those neurons isolated from the hemispheres are generally stabilized between 5 and 12 ms (Fig. 5).

• 6. Electrical stimulation of the auditory cortex evokes discharges from a recorded cerebellar auditory neuron (Fig. 6). Cortical stimulation also facilitates the response of an acoustically evoked cerebellar neuron by increasing its number of impulses (Fig. 7). The degree of facilitation is dependent upon the amplitude of the acoustic stimulus (Fig. 8).

• 7. For a given electrical and acoustic stimulation condition, the facilitative latency and the degree of facilitation varied with the interstimulus interval. Among 23 neurons studied, most of them (19 neurons, 82.6%) had a maximal facilitative latency between 2 and 10 ms (Fig. 9B).

• 8. By examining the difference in the facilitative effect in each isolated cerebellar auditory neuron before and after a topical application of local anesthetic, procaine, onto the point of electrical stimulation in the auditory cortex, we found that the facilitative pathways to vermal and hemispheric neurons may be different from the pathway to parafloccular neurons (Figs. 10, 11).

• 9. Possible auditory pathways to different parts of the cerebellum are discussed in relation to the wide range of recorded response latencies.

• 10. The facilitative influence of the auditory cortex on the cerebellar auditory neurons is assumed to enhance the cerebellar role in acoustic motor orientation.