Human cortical regions activated by wide-field visual motion: an H2(15)O PET study

Abstract

1. Several areas in the monkey dorsal visual pathway, including the dorsal part of the medial superior temporal area, have been found to contain cells responding to movements of a wide visual field and are suggested to be involved in analyzing self-induced motion information. In the present study, positron emission tomography was used to localize human cortical regions responding to wide-field visual motion. Changes in regional cerebral blood flow (rCBF) were measured when subjects maintained fixation and viewed low-contrast (0.15 log units brighter than the background) dots subtending 80 x 80 degrees and moving either coherently or incoherently. Brain foci were localized after activity in a fixation-only paradigm was subtracted from that in the two moving dot paradigms. 2. Both the coherent and incoherent movements significantly activated the primary/secondary visual cortex and surrounding visual areas in the cuneus and superior occipital gyrus. Subtraction of images between the coherent and incoherent movements showed that the activity caused by the two types of movement was comparable in these early visual cortical regions. 3. In the lateral occipitotemporoparietal cortex, the coherent movement specifically activated two separate areas; a posterior focus was located at the border of the right occipitotemporal gyri, and a dorsoanterior focus was located bilaterally in the temporoparietal cortex. The incoherent movement did not activate these regions. 4. A fine anatomic localization using individual magnetic resonance images was performed for the bilateral activation in the temporoparietal cortex, which was found to be located mainly in the depth of the inferior parietal lobule and a small portion of the superior and middle temporal gyri. 5. Both the coherent and incoherent movements activated a part of the superior parietal lobule located within the intraparietal sulcus (Brodmann area 7). The bilateral foci activated by the coherent movement were located more anteriorly than the focus activated by the incoherent movement. Subtraction images between the coherent and incoherent movements, however, did not reveal any significant rCBF increases in the superior parietal lobule. 6. Several other cortical regions known to be involved in visuospatial and visuomotor functions were also activated by the coherent movement, including the frontal eye field (Brodmann area 8) and premotor cortex (Brodmann area 6) in the frontal lobe. 7. The posteriorly located activation at the border of occipito-temporal gyri corresponds to the homologue of the middle temporal area reported in previous activation studies using small to medium-sized motion stimuli. The bilateral activation in the inferior parietal lobule appeared to rely on wide-field motion stimulation.

A cortical area that responds specifically to optic flow, revealed by fMRI

“…The cortical areas that responded to flow motion and translation were distinct. The region that responded to translation was similar to the region reported in other studies that used dynamic controls 16,22 . On the other hand, the region that responded to flow stimuli was separated by more than 1 cm from the area responding to translation, and was usually more ventral.…”

“…A very strong motion-selective response at the boundary of Brodmann's areas 19 and 37 is shown by human imaging [15][16][17][18][19][20][21][22][23] . This area is generally thought to be the human analogue of monkey V5/MT-MST regions, and is referred to as 'V5/MT complex' (MT+).…”

“…2a). The response extended for more than 1 cm along the sulcus that separates Brodmann's area 19 and 37, within the region that is usually referred to the human analogue of V5/MT complex [15][16][17][18][19][20][21] . Figure 2d shows the response time course, averaged over nine subjects; even when measured against a control that was well matched for local motion, there was a strong and specific fMRI response within the V5/MT complex, suggesting specialized detectors for this type of motion.…”

“…In agreement with the neurophysiological studies, these units have very large receptive fields 12 and sum information over periods of one or two seconds (L. Santoro and D.C. Burr, Perception 28, 90c, 1999). There is also some evidence in humans for selectivity along the 'cardinal directions' of optic flow (radial and circular) 13 , although this issue is somewhat controversial 14 .A very strong motion-selective response at the boundary of Brodmann's areas 19 and 37 is shown by human imaging [15][16][17][18][19][20][21][22][23] . This area is generally thought to be the human analogue of monkey V5/MT-MST regions, and is referred to as 'V5/MT complex' (MT+).…”

“…This area is generally thought to be the human analogue of monkey V5/MT-MST regions, and is referred to as 'V5/MT complex' (MT+). Other motion-sensitive areas have been identified: a dorsal region referred to as V3A 16,21,22,24 and a ventral region, seemingly activated by motion boundaries and second-order motion 20,21 . Here, using fMRI, we examined the response to optic-flow stimuli, and showed selective activation of a large area within the V5/MT complex to radial and circular motion, very different from the area activated by translational motion.…”