The posterior parietal cortex (PPC) plays an important role in the transformation of spatial representations from perception to action. Taken together, our findings suggest a reorganization of oscillatory activity during spatial updating.
In particular, activity in the lateral intraparietal area (LIP) of monkey PPC and homologous areas in the human PPC has been associated with specialized spatial functions, including the control of spatial attention (Silver and Kastner 2009; Bisley and Goldberg 2010; Liu et al. Twenty-two naïve participants (7 females/15 males; mean age 26.5 years), free of any neurological or psychiatric disorders, volunteered to participate in the study.
These experiments suggest that stimulation of IPSp distorts an eye position or displacement signal that updates the representation of space at the completion of a saccade.
worst speed dating questions - Spatial updating in human parietal cortex
Using magnetoencephalography, we tested this hypothesis by studying the modulations in oscillatory activity in a spatial updating task. But without varying eye position, the question remains unanswered whether these oscillations are related to the construction of a gaze-independent spatial representation or are a manifestation of the saccade goal encoded in gaze-centered coordinates.
Human subjects had to remember the location of a target, briefly flashed left or right of central fixation. At the population level, rhythmic neuronal synchronization may provide a mechanism to selectively amplify and gate behaviorally relevant representations in parietal processing (Buzsáki 2006). To discriminate between these 2 possibilities, we applied MEG to record oscillatory brain activity from human subjects while they produced intervening saccades between viewing a goal target and generating an eye movement toward its remembered location.
Next, they refixated and then, after a further memory delay, made a saccade to the memorized target location. Gain field modulations, the scaling of neuronal firing rates by eye and head position, have been suggested to implicitly transform these spatial representations into other gaze-independent (e.g., head/body-centered) reference frames (Andersen et al. In general, gamma-band oscillations (40 Hz) have been implicated in active local processing, maintaining and emphasizing a neural representation (Fries 2009), while alpha-band oscillations (8–12 Hz) reflect functional inhibition and gating (Klimesch et al. With regard to monkey area LIP, intracranial local field potential recordings have shown that neurons synchronize their activity in a spatially tuned manner during the coding of a working memory for a saccade (Pesaran et al. Using magnetoencephalography (MEG), corresponding observations have been made in human PPC, indicating a bias of spectral power to contralateral target locations (Medendorp et al. While the target remained stable in gaze-independent coordinates (i.e., relative to head/body), its remembered location must be updated to compensate for the intervening saccade in gaze-centered coordinates.
We observed gamma-band (40 Hz) synchronization and alpha-band (8–12 Hz) desychronization in contralateral occipital and parietal areas, both showing updating in a gaze-centered reference frame but with fast and slow time courses, respectively. By exploiting the hemispheric lateralization of the power in the various frequency bands, we compared conditions in which the remembered location of the target reverses sides relative to the gaze-fixation point versus conditions in which the target remains at the same side after the intervening eye movement.
The two most striking consequences of PPC damage are apraxia and hemispatial neglect.