Projection of precentral, premotor and prefrontal cortex to the basilar pontine grey and to nucleus reticularis tegmenti pontis in the monkey (Macaca fascicularis).

In the present autoradiographic study the projections from frontal lobe cortex to basilar pontine grey (GP) and to N. reticularis tegmenti pontis (RTP) have been traced in 24 monkeys. GP receives marked ipsilateral and scant contralateral projections from primary motor as well as from premotor cortex (including supplementary motor area and frontal eye field). This projection terminates in the form of thin lamellae which are folded along the longitudinal axis and which receive the input in a partly separate and partly overlapping somatotopical order. These lamellae provide the enlarged interface which seems necessary for the interaction and the processing of information converging from frontal cortex of the two hemispheres and dealing with posture and movement of functionally related parts of limbs and body. Comparatively weak and widely spread ipsilateral projections are noted from prefrontal area 9. This may indicate a functionally significant difference of prefrontal cortex with respect to the "dynamic operation of cerebro-cerebellar circuitry" (Eccles). The fronto-cortical projections to RPT and to the caudal pole of GP are also described.