Maintaining internal representations: the role of the human superior parietal lobe

Abstract

In sensorimotor integration, sensory input and motor output signals are combined to provide an internal estimate of the state of both the world and one's own body. Although a single perceptual and motor snapshot can provide information about the current state, computational models show that the state can be optimally estimated by a recursive process in which an internal estimate is maintained and updated by the current sensory and motor signals. These models predict that an internal state estimate is maintained or stored in the brain. Here we report a patient with a lesion of the superior parietal lobe who shows both sensory and motor deficits consistent with an inability to maintain such an internal representation between updates. Our findings suggest that the superior parietal lobe is critical for sensorimotor integration, by maintaining an internal representation of the body's state.

Dual-tasking postural control: Aging and the effects of cognitive demand in conjunction with focus of attention

“…A well-established view suggests that the brain utilizes internal representations of forward motor commands and multi-sensory feedbacks to monitor, update, calibrate, and maintain the body's position (e.g., [37,72,74]). Findings derived from spatial-neglect patients who suffer from postural instability suggest in particular the involvement of parietal cortical functions in postural control probably implicating internal body representations [27,38,44,65,66,73,75]. In addition to maintaining the internal body representation in 3D space, parietal lobe functions may also underlie covert preparatory motor attention [55,56], somewhat analogous to their roles in covert orienting of visual attention [46].…”

Intact spatial updating during locomotion after right posterior parietal lesions

“…This indicates that the right PPC is not critically involved in updating self-location along straight paths. We found this surprising, considering the aggregation of evidence for impaired eye and arm position updating after PPC lesions [15,16,29,65]. Before abandoning the notion that the PPC is a critical structure for updating during locomotion, however, other types of locomotion and more complex trajectories should be tested.…”

“…Future testing with left hemisphere patients promises to shed light on this issue. Evidence is scant for lateralization of the neural substrates of arm position updating, but there are reports that lesions to or stimulation of the left PPC can lead to de®cits in updating during reaches [15,65], at least for reaches made by the contralateral arm.…”

“…This prior knowledge could have an important facilitory e ect upon updating. One possibility is that this information is used to generate a neural representation of the predicted extent of self-motion (i.e., a goal state for the path integrator) [65]. During the walk, the selfmotion that is sensed on-line can then be compared with the predicted value.…”

“…Neuropsychological work and transcranial magnetic stimulation studies suggest that the PPC functions to maintain an updated estimate of the current position of the arms [15,65]. In both monkeys and humans, lesions to certain regions of the PPC can produce a disorder of reaching behavior, known in humans as optic ataxia [19,27,32,42].…”