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Abstract

The lateral premotor cortex of the macaque monkey is an anatomically multifaceted area, which serves multiple sensorimotor and cognitive functions. While evidence for the functional organization of human premotor cortex accumulates, much less is known about the underlying anatomical properties of this brain region. Based on the findings in macaques, we hypothesized the existence of at least two major fields, corresponding to the ventral and the dorsal lateral premotor cortex, the border between which is still a matter of debate in the human brain. Since a further subdivision running orthogonally in the rostro-caudal direction has been suggested and often reconfirmed in macaques, we set out to find whether our data would also support four distinct fields on the lateral convexity. We used diffusion tractography and functional Magnetic Resonance Imaging (fMRI) to investigate whether the supposed homologue area in humans can be segregated on the basis of anatomical connectivity and functional activation in a set of cognitive and motor tasks. Tractographic data suggested a distinction between ventral and dorsal premotor cortex, as well as inferior and superior sub-parcellation of both. Functional MRI data corroborated these four areas, showing that anatomical parcellation based on the tractography predicts the distribution of functional activation and vice versa. Functional data from movement of different body parts, prediction of rhythmic, object-based or spatial sequences, and observation of different types of movement of an actor were largely consistent with the interpretation of -based parcellation of four sub-regions in the human precentral gyrus (PCG). However, they also showed that functional activations were not sharply restricted to these fields. In line with evidence from macaque research, we therefore suggest that even under optimal signal-to-noise ratio, the contributions of the sub-regions of the PCG are differently weighted for different functional requirements rather than exclusively engaged in only the one or the other function or task. In sum, results may encourage the application of combined diffusion tractography and fMRI in vivo in order to shed light on the correspondence of brain function and anatomy.