Neuroscientists at University College London (UCL) have identified the posterior parietal cortex as the principal brain region responsible for building a real-time map of the body in space. Using brief magnetic stimulation applied through coils placed on participants’ scalps while they experienced controlled touches and limb movements, the team tested how the brain combines touch with information about limb position. Their results show that the posterior parietal cortex plays a central role in judging where body parts are relative to one another and to external space. These findings are relevant to research on proprioception, developmental coordination disorder, body dysmorphic disorder, phantom limb sensations, balance and related conditions.
Part of the brain that tracks limbs in space discovered
Researchers pinpoint the parietal cortex as the area that integrates touch and limb position to track body posture through space.
Everyday actions—like brushing a mosquito off your arm without looking—depend on the brain’s ability to combine tactile input with internal information about limb position. This integration creates a dynamic “body map” that lets us know where our hands and limbs are even with our eyes closed. The UCL team, working with collaborators in Barcelona, investigated how the brain constructs this map by temporarily disrupting activity in a targeted part of the parietal cortex and measuring how that disruption affected people’s judgements about touch and body location.
In their experiment, volunteers’ forearms rested in a sling that could be raised or lowered to change the arm’s spatial relation to the face. The researchers applied brief taps at various points along the forearm and then shortly afterward at different sites on the face. Participants were asked to report whether the touch on the arm occurred above or below the touch on the face. Making that judgement requires combining where each touch occurred on the skin with the current position of the arm—the very process the team aimed to test.
After the first tap on the arm and before the face tap, the scientists delivered a short pulse of magnetic stimulation to the posterior parietal cortex (PPC) in the right hemisphere, using a coil positioned over the PPC location based on each participant’s brain scan. This transient interference did not alter participants’ basic ability to feel a touch or to indicate a location on the skin. Instead, it specifically impaired their ability to judge the spatial relationship between the arm and face taps—evidence that the PPC is required to combine touch and limb position into an egocentric map of the body in space.
Professor Patrick Haggard of the UCL Institute of Cognitive Neuroscience, who led the UCL team, explained that our brains continuously update the posture of the body so that we maintain an internal sense of where our limbs are. The study demonstrates how the brain performs that update: the posterior parietal cortex remaps tactile signals into external, body-centered space by integrating touch with proprioceptive cues about limb position.
The study’s findings have clear implications for clinical and developmental research. For children with developmental coordination disorder, for example, difficulties coordinating movement may stem in part from an impaired internal sense of limb position. By identifying a specific parietal region involved in constructing the body map, this research points to a neural target for further study and potentially for interventions aimed at improving spatial awareness of the body. Likewise, better understanding how tactile and positional signals are combined could inform research into phantom limb sensations, balance disorders and conditions that involve altered body perception.
The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the findings are reported in the journal Current Biology. The paper, titled ‘The Posterior Parietal Cortex Remaps Touch into External Space’, details how transient disruption of PPC activity selectively impairs judgements that require combining touch with limb position, while leaving simple touch detection and limb-location judgements intact.
Source: University College London