Functional anatomy of the macaque temporo-parieto-frontal connectivity

The primate parietal lobe is primarily dedicated to the processing of sensory information for the guidance of motor behavior, based on the integration of sensory with motor signals (sensorimotor transformations), mediated by specific, strong, and reciprocal connections with the motor cortex. Sensorimotor transformations have been regarded as an automatic process carried out independently from the temporal cortex, which is considered the location where sensory information is used for perceptual processes. However, both human and non-human primate studies have shown interactions between these two regions in different aspects of sensorimotor and cognitive processes. Connectional studies in macaques have provided a detailed description of the possible neural substrate for these interactions. Specifically, temporo-parietal connections almost exclusively involve the inferior parietal lobule (IPL) and display a fine topographic organization, providing the substrate for the role of the macaque IPL in “perception-based” control of motor behavior. Particularly, more rostral IPL areas are involved in motor and cognitive motor functions related to hand action organization and oculomotor control as well as in action and intention understanding, whereas more caudal IPL areas are involved in multisensory integration for the construction of space representations for guiding arm and eye motor behavior. Temporal and IPL-interconnected areas also share connections with specific ventral frontal areas and are thus part of large-scale cortical networks in which the various nodes are linked through “dorsal” temporo-parieto-frontal and “ventral” temporo-frontal pathways. Anatomical and functional studies suggest homologies between human and macaque temporo-parieto-frontal connectivity; they also suggest that higher-order functions of the human IPL could have evolved from the exploitation and adaptation of phylogenetically older neural mechanisms that occur in macaque brains. Thus, connectional data from macaque studies appear essential for understanding human brain mechanisms, even in cases of cognitive abilities undeveloped in other animals, and for interpreting clinical data, including disconnection syndromes.