Somatotopic studies on the vermal cortex of the cerebellar anterior lobe of unanaesthetized cats

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Abstract
In unanaesthetized cats with intact neuraxis the relation between the cutaneous receptive fields of Purkyně cells and the position of these cells in the vermis of the cerebellar anterior lobe was studied with the specific question whether this cerebellar area exhibits any kind of somatotopy in the absence of central anaesthesia. To establish the receptive fields the skin of all four limbs and of the trunk was probed with mechanical stimuli (taps, air-jets, pressure). The recording sites in the vermis were determined histologically. In regard to the mossy fiber transmitted input none of the four limbs showed a dominant representation in one or more of the lobules rostral of the fissura prima or in a parasagittal section. For the ipsilateral limbs there is a greater mossy fiber input to lobule V from the forelimb than from the hindlimb (84 ∶ 59%), and a reversed preponderance for lobule II (45 ∶ 80%) but this indication of a somatotopic arrangement is not unequivocally paralleled by the other mossy fiber inputs. Also in regard to the climbing fiber input no distinct somatotopical arrangement has been detected. Again it has been noted that the ipsilateral inputs have a somewhat greater input to lobule V from the forelimb than from the hindlimb (35 ∶ 22%), and the reverse finding holds true for lobule II (10∶ 45%). The overall results did not change appreciably when the responses were grouped according to their latencies or when the Purkyně cells were classified according to the patterns of convergence of their receptive fields. The absence of a distinct somatotopic organization in the vermis is a direct consequence of the considerable convergence from the cutaneous mechanoreceptors of the limbs onto the individual Purkyně cells which occurs via the mossy and the climbing fiber pathways. It is suggested that this convergence indicates that the vermal Purkyně cells are particularly involved in coordinating the motor activity of forelimbs and hindlimbs.