In a nutshell: The brain area responsible for visually guided movements – such as reaching, pointing and grasping – is divided into three subregions with distinct yet complementary roles.

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The simple act of reaching for an object involves a complex process of perceiving its distance and depth, before moving to grasp it without knocking it over or missing it entirely. The part of the brain responsible for these visually guided arm movements is called the parietal reach region (PRR).

Studying the PRR is helpful not only for understanding human behaviour but also for designing prosthetic and robotic arms. However, despite considerable interest in the PRR, its structure and organization were not well understood.

An international group of researchers, led by Brain Function CoE chief investigator Marcello Rosa and associate investigator Sofia Bakola at Monash University, aimed to increase understanding of the PRR by clarifying the boundaries between its subregions. The team used fluorescent tracers in the brains of macaque monkeys to follow the connections between nerve cells in the PRR and other parts of the brain.

The team found that the PRR covers three distinct subregions that each receive inputs from multiple brain areas involved in sensation, vision and movement. Although their patterns of connectivity are different, some of their functions overlap or are complementary.

These results extend the findings of previous studies by further refining the structure of these subregions – and their functions in the brain.

Next steps:
The team will record brain activity in the PRR subregions in animals that are reaching and grasping objects of different shapes, to determine what is encoded in each area and how information flows between them.

Bakola, S., Passarelli, L., Huynh, T., Impieri, D., Worthy, K. H., Fattori, P., Galletti, C., Burman, K. J., & Rosa, M. G. P. (2017). Cortical afferents and myeloarchitecture distinguish the medial intraparietal area (MIP) from neighboring subdivisions of the macaque cortex. eNeuro, 4(6), ENEURO.0344-17.2017. doi: 10.1523/ENEURO.0344-17.2017

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