Multiple representation in the nucleus lateralis of the cerebellum: an electrophysiologic study in the rat.

The motor organization of the nucleus lateralis (NL) of the rat's cerebellum was investigated by observing the motor effects of electrical microstimulations of the NL. The movements evoked by the NL mainly concerned forelimb and head segments. Only in a few cases were movements of hindlimb segments evoked. Motor effects were obtained according to a precise topographical pattern. This pattern delimited functional zones, or representations, within the NL, each zone being specifically related to a particular segment of the body. A few body segments were activated from single zones only (single representation) whereas some other body segments could be activated from different zones of the NL. Among them, the axio-proximal body segments were activated in a similar way from all sites (multiple representation) whereas the distal body segments were differently activated from the various representation zones (specific representation). The multiple and specific representations were distributed between the 3 cytoarchitectonic subregions of the NL (NLm, DLH and slp) in such a way that the body segments were usually represented only once in each individual NL subregion. Each NL subregion included sets of representations concerning body segments characterized by a topographical continuity (e.g. the different segments of the forelimb in both DLH and slp). Thus, the individual NL subregions may bring into play coordinate plurisegmental muscular activities of the limbs and/or of the head. The NLm controls movements of all the segments of the head and those of axio-proximal segments of both limbs. The DLH particularly controls movements of the head, including both the proximal (neck) and the oral regions. To a lesser degree, DLH controls movements of the various segments of the forelimb, including synchronous flexion of all the digits. The slp is specifically involved in the control of motor activities of: i) the proximal segment of the head (rotation of the neck) as well as its distal segments (displacement of individual vibrissae, rotation of the ear pinna) and ii) the various segments of the forelimb including individual digits. Functionally, the proximal segments would be concerned in the spatial displacement of the limbs or of the head whereas the distal segments would be involved in the realization of precise and discrete movements related to specific functions of the distal segments concerned. The 3 subregions of the NL may be concerned in different motor functions.(ABSTRACT TRUNCATED AT 400 WORDS)