The middle temporal visual area(MT)in the bushbaby, Galago senegalensis.

Recently we discovered a topographic representation of the visual field in the temporal cortex of the owl monkey, Aotus trivirgatus, which we termed the 'middle temporal visual area' (M1)I. Such a systematic representation has not yet been demonstrated in the temporal cortex of other primates, although the probable 12 existence of MT is indicated in several other primates by fiber connection patterns10, 15, architectonic characteristicslo, and cortical evoked potentialsI3.l4. We attempted to identify MT in the bushbaby, Ga/ago senega/ensis, because we wondered if this temporal visual area arose early in primate (or mammalian) evolution or was re­ stricted to the Anthropoidea. Also, a projection from the inferior pulvinar to cortex in the expected loca tion of MT has been demonstrated in the bushbaby6, 7. Since cor­ tical projections from the pulvinar have been regarded as a major source of visual input to temporal 'association' cortex5•7, it seemed important to explore the or­ ganization of this projection zone of the inferior pulvinar in the bushbaby. !.:i The electrophysiological mapping methods used in this study were identical to I~'::: I l_ .: i those used previously for the owl monkeyl. The topography of the representation of 11; I the visual field in MT was deter~ined by relating the positions of receptive fields for ! ":':," ~ single neurons or small clusters of neurons recorded with microelectrodes. to· the i':::' locations of corresponding recording sites. MT was mapped in 4 adult bushbabies, , which were anesthetized with urethan. Small electrolytic lesions (20 p.A for 10 sec) were made at recording sites which had receptive fields near the vertical meridian or the extreme temporal periphery of the visual field. The experimental brains were " :: ~ perfused with formol-saline, dehydrated, embedded in celloidin, and alternate series u of 30 p.m sections were stained with thionine for cell bodies or hematoxylin for myelin (Heidenhain-Woelcke technique). , .......-~ The electro physiological and architectonic results clearly identified a region of the temporal lobe of the bushbaby as the middle temporal visual area. The location