Abstract
IntroductionAn essential complement to molecular-genetic approaches for analyzing the function of the oculomotor circuitry in mice is an understanding of sensory and motor signal processing in the circuit. Although there has been extensive analysis of the signals carried by neurons in the oculomotor circuits of species, such as monkeys, rabbits and goldfish, relatively little in vivo physiology has been done in the oculomotor circuitry of mice. We analyzed the contribution of vestibular and nonvestibular signals to the responses of individual Purkinje cells in the cerebellar flocculus of mice.MethodsWe recorded Purkinje cells in the cerebellar flocculus of C57BL/6 mice during eye movement responses to vestibular and visual stimulation.ResultsAs in other species, most individual Purkinje cells in mice carried both vestibular and nonvestibular signals, and the most common response across cells was an increase in firing in response to ipsiversive eye movement or ipsiversive head movement. When both the head and eyes were moving, the Purkinje cell responses were approximated as a linear summation of head and eye velocity inputs. Unlike other species, floccular Purkinje cells in mice were considerably more sensitive to eye velocity than head velocity.ConclusionsThe signal content of Purkinje cells in the cerebellar flocculus of mice was qualitatively similar to that in other species. However, the eye velocity sensitivity was higher than in other species, which may reflect a tuning to the smaller range of eye velocities in mice.
Highlights
An essential complement to molecular-genetic approaches for analyzing the function of the oculomotor circuitry in mice is an understanding of sensory and motor signal processing in the circuit
Summation of vestibular and eyemovement related signals in a Purkinje cell Despite the nonlinearities described above, Purkinje cell responses in the floccular complex of monkeys and goldfish can be well-approximated by a linear summation of the responses to the head velocity and eye velocity inputs (Lisberger and Fuchs 1978a; Miles and Eighmy 1980; Pastor et al 1997; Hirata and Highstein 2000). We evaluated this in mice by testing the extent to which the response of each Purkinje cell during VOR cancellation (VORC) could be predicted from the responses during VOR in total darkness (VORD) and optokinetic reflex (OKR)
We assessed the signal content of floccular Purkinje cells in awake mice performing eye movement responses to both vestibular and visual stimuli
Summary
An essential complement to molecular-genetic approaches for analyzing the function of the oculomotor circuitry in mice is an understanding of sensory and motor signal processing in the circuit. We analyzed the contribution of vestibular and nonvestibular signals to the responses of individual Purkinje cells in the cerebellar flocculus of mice. Results: As in other species, most individual Purkinje cells in mice carried both vestibular and nonvestibular signals, and the most common response across cells was an increase in firing in response to ipsiversive eye movement or ipsiversive head movement. The cerebellum contains roughly half of all neurons in the brain (Lange 1975), yet it has a relatively simple circuit architecture, which makes it a tractable model for studying the function of neural circuits. A critical complement to the use of molecular-genetic approaches in mice is an understanding of the signal processing in the VOR circuit
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