MICROCIRCUITRY AND FUNCTION OF THE INFERIOR OLIVE

The inferior olive, which provides the climbing fibers to Purkinje cel ls in the cerebellar cortex, has been implicated in various functions, such as learning and timing of movements, and comparing intended with achieved movements. For example, climbing-fiber activity could transm it error signals during eye-blink conditioning or adaptation of the ve stibule-ocular reflex, or it could carry motor command signals beating on the rhythm of the oscillating and synchronous firing of ensembles of olivary neurons, or both. In this review, we approach the controver sial issue of olivocerebellar function from the perspective of the uni que organization of the microcircuitry of the olivary neuropil,The cha racteristic glomeruli are formed by a core of long dendritic or axonal spines, each of which is innervated by both an inhibitory terminal de rived from the hindbrain and an excitatory terminal derived from eithe r an ascending or descending input. The dendritic spines, which origin ate from dendrites with varicosities carrying dendritic lamellar bodie s, are coupled by gap junctions. By drawing a comparison with a comput ational model by Segev and Rall, which might be applicable to the typi cal olivary spine with its unique morphological features and combined excitatory and inhibitory input, we propose that the microcircuitry of the inferior olive is capable of functioning both in motor learning a nd motor timing, but does not directly compare intended with achieved movements.