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Notizen: Abstract 1. The responses of neurons located in the rostral part of the fastigial nucleus to sinusoidal tilt of the animal were recorded in precollicular decerebrate cats and compared with those elicited by the same stimulation in Purkinje (P) cells located in the vermal cortex of the cerebellar anterior lobe. In particular, by fixing the head and the body of the animal to the tilting table and by rotating the animal around its longitudinal axis, it was possible to elicit a selective labyrinth input without eliciting a neck input. 2. Among the 60 fastigial neurons tested, 43 units responded to sinusoidal tilt at the frequency of 0.026 Hz and at the peak amplitude of displacement of 10°–15°. On the other hand, among 106 P-cells tested for a mossy fiber (MF) response to the labyrinth input, 32 units were affected by the same parameters of stimulation. In both instances the response consisted in a periodic modulation of the discharge frequency, which was related to the position of the animal. Most of the responses of the fastigial units to the labyrinth input were characterized by a peak excitation in phase with side-down tilt of the animal and by inhibition during side-up tilt, whereas most of the MF-responses of the P-cells to the labyrinth input showed just the opposite behavior. 3. The threshold amplitude of tilt responsible for these responses varied in different units from 1° to 3° at the frequency of 0.026 Hz. The sensitivity of the first harmonic of the unit responses to tilt, expressed in percentage change of the average firing rate per degree of displacement, corresponded on the average to 1.73±1.16, S.D., for the fastigal neurons and to 1.61±0.94, S.D., for the P-cells. These values did not change or were only slightly modified as a result of increasing amplitude of stimulation from 1°–3° to 15°–25° at a frequency of 0.026 Hz. Moreover, changes in amplitude of stimulation at the parameters reported above did not greatly modify the phase angle of the first harmonic of the responses relative to the side-down position of the animal. Units located in the medial corticonuclear zone of the cerebellum did not show any change in sensitivity and phase angle of the responses by increasing the frequency of tilt from 0.015 to 0.20 Hz at the fixed amplitude of 10°–15°, thus indicating that these responses depended upon stimulation of macular receptors. In other units, however, these changes in frequency of rotation modified the phase angle of the responses, which became related to velocity rather than to the positional signal, due to stimulation of semicircular canal receptors. 4. The observation that most of the responsive fastigial neurons increased their firing rate, while most of the responding P-cells located in the vermal cortex of the cerebellar anterior lobe decreased their firing rate during side-down rotation of the animal is discussed in relation to the postural changes of the limbs elicited during asymmetric stimulation of macular receptors.