Spatial updating in human parietal cortex
Taken together, our results suggest that power in the gamma band is instantly reorganized to encode task-relevant visuomotor space in a gaze-centered reference frame, while power in the alpha band reflects a regulatory mechanism actively facilitating the gating of the saccade target and inhibiting the original stimulus representation.The posterior parietal cortex (the portion of parietal neocortex posterior to the primary somatosensory cortex) plays an important role in planned movements, spatial reasoning, and attention.
The superior parietal lobule and inferior parietal lobule are the primary areas of body or spacial awareness.Saccadic eye movements cause sudden and global shifts in the retinal image. This “spatial updating” mechanism ensures that spatial codes for perception and action are not compromised by eye movements.Rather than causing confusion, however, eye movements expand our sense of space and detail. Spatial updating occurs in the lateral intraparietal area (LIP) as well as several other cortical and subcortical regions of the monkey brain, including the frontal eye fields (FEF) (12), the parietal reach region (8, 13), extrastriate cortex (14), and the superior colliculus (15).At the population level, rhythmic neuronal synchronization may provide a mechanism by which PPC could selectively emphasize the task-relevant reference frame in spatial processing.Using magnetoencephalography, we tested this hypothesis by studying the modulations in oscillatory activity in a spatial updating task.In another single-cell recording experiment, neurons in parietal reach region exhibited responses consistent with either of two target locations in a sequence of planned reaching movements, suggesting that different parts of a planned sequence of locations can be represented in parallel in parietal reach region.
The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals.
The posterior parietal cortex is divided by the intraparietal sulcus to form the dorsal superior parietal lobule and the ventral inferior parietal lobule.
In addition to separation based on effector type, some regions are activated during both decision and execution, while other regions are only active during execution.
Similarly, parahippocampal and retrosplenial regions, together with specific parietal subregions such as the precuneus, are selectively involved in a specific form of allocentric representation in which object locations are encoded relative to enduring spatial features of a familiar environment (“environmental referencing”).
We also present a novel functional magnetic resonance imaging study showing that these regions are selectively activated, whenever a purely perceptual spatial task involves an object which maintains a stable location in space during the whole experiment, irrespective of its perceptual features and its orienting value as a landmark.
By varying the onset time of stimulation, we show that the representation of space in IPSp is updated immediately after the first-saccade. In the current study, we stimulated the human IPS of the right hemisphere with TMS and measured effects on spatial updating using a variant of the “double-step saccade” task ().