In particular, the prefrontal cortex (PFC) and posterior parietal cortex (PPC) have been the focus of recent research efforts. Growing evidence indicates that visual working memory is distributed over multiple brain regions 3, 4, 5, 6, 7. Visual working memory is a capacity-limited, temporary buffer that maintains and manipulates visual information for a short period 1, 2. Our findings suggest that the prefrontal cortex holds behaviorally relevant abstract representations while visual representations in posterior and visual areas are modulated by the task demands. In contrast, both dynamic and stable coding are found in the continuous estimation task. In occipitoparietal electrodes, however, we find that remembered features are dynamically coded over time, whereas neural coding of the ensemble mean is absent in the old/new judgment task. Here, we consistently observe stable coding of simple features as well as the ensemble mean in frontocentral electrodes, which even correlated with behavioral indices of the ensemble across individuals. Ensemble representations provide a unique opportunity to investigate structured representations of working memory because the visual system encodes high-order summary statistics as well as noisy sensory inputs in a hierarchical manner. The light stimuli include flashes of light (flash ERG) and flickering lights.We characterized the population-level neural coding of ensemble representations in visual working memory from human electroencephalography. The visual stimuli vary some are done with no light in the background (dark-adapted, or scotopic readings), and some are done with light in the background (light-adapted, or photopic readings). The ERG machine records the resulting electric signals' amplitude (voltage) and time course. Retinal cells emit small electrical signals when stimulated by certain types of light. The physician places an additional electrode on the forehead skin.ĭuring an ERG recording session, the patient looks into a bowl displaying different amounts of light. The doctor then props the eyelids open with a speculum and gently places a contact lens electrode or an electrode resembling a fine thread on each eye. An eye doctor dilates the patient's eyes with standard dilating eyedrops. The patient assumes a comfortable position either lying down or sitting up. ERG is usually well tolerated, painless, and medical professionals can perform ERG even in cooperative children and infants. Depending on which eye condition is being studied, ERG may be performed in conjunction with other tests, such as electrooculography (EOG) or dark adaptometry testing. How do health care professionals perform an ERG?ĮRG is one type of ophthalmic electrophysiology test.
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