Parieto-occipital cortex activation during self-generated eye movements inthe dark

A number of extrastriate visual areas in the parietooccipital cortex are kn own from single-cell recordings of the macaque monkey to be involved in the coding of eye-position signals in the brain. These are important for the a ccurate location of visual objects in extrapersonal space, It can be predic ted that these areas will show increased activation during the performance of eye movements at high frequency. In the present study PET and measuremen ts of the regional distribution of cerebral blood flow (rCBF) were used as indirect measures of neural activity. Two independent groups of normal volu nteers performed large-amplitude self-generated eye movements in complete d arkness, thus removing the confounding effects of visual stimulation on par ietooccipital activation. The first group (group A; n = 5) served as a hypo thesis-generating group and the second group (group B; n = 4) served as a h ypothesis-testing group, The data were analysed using statistical parametri c mapping at a significance level corrected for multiple comparisons (group A, Z > 4.08; group B, Z > 4.04), Significant rCBF increases were found for both groups in the frontal eye fields, supplementary eye fields, cerebella r vermis and putamina/thalami. Additionally, activation was found in the cu nei in the posterior bank of the parieto-occipital sulcus, Also, the extrao cular muscles were activated and, as a consequence of the partial volume ef fect, projected to the orbitofrontal cortices, At a less conservative thres hold, activation was found close to the intraparietal sulci on the left sid e (Z = 3.91, P = 0.09) and right side (Z = 3.33, P = 0.42), The locations o f these areas were confirmed in group B with reference to high-resolution s tructural MRI scans. The activation of the parieto-occipital cortex without overt visual stimuli is interpreted as the result of neural activity relat ed to the reception of efferent copies of motor commands and/or the activat ion of neurons coding for eye position relative to the orbits. These are im portant constituents for the location and remapping of visual stimuli in sp ace.