Centrifugal Fibres in the Lateral Olfactory Tract

Abstract

FOR the interpretation of results of electrophysiological studies of the responses in the olfactory bulb to stimulation of the lateral olfactory tract it is a matter of some importance to know whether this tract consists solely of efferent fibres from the bulb or whether it also contains centrifugal fibres to the bulb^1–3. Such centrifugal fibres were described by Cajal⁴, who, although uncertain of their origin, clearly distinguished them from those in the anterior commissure (which, coming from the opposite olfactory bulb, should be considered as commissural). The commissural fibres have been demonstrated experimentally by several workers; but with one exception⁵ the presence of centrifugal fibres in the lateral olfactory tract has been either denied or overlooked. However, as all reports agree that after interruption of both the anterior limb of the anterior commissure and the lateral olfactory tract the degeneration is heavier in the ipsilateral than in the contralateral olfactory bulb^5–7, it is clear that a proportion of the fibres to the bulb must be arising in the ipsilateral hemisphere, but it is not known to what extent these run in the lateral olfactory tract or in the anterior commissure. In order to determine if centrifugal fibres run in the lateral olfactory tract it is necessary to place lesions which are strictly limited to the tract.