To the editor:

Astafiev et al.1 report that unseen, visually guided motor acts activate the extrastriate body area (EBA)2. This finding has potential implications for understanding the interactions between motor and perceptual systems and suggests a mechanism by which the visual stimulation resulting from one's own motor acts is distinguished from that produced by others3. We replicated the experiment of Astafiev et al. and found, in line with their findings, action-related modulation in the EBA. However, a closer look showed that the region involved in visually guided motor acts is distinct from the EBA and that action-related modulation and body selectivity are unrelated.

We scanned 13 subjects with an fMRI localizer for the EBA (contrasting headless bodies with faces, scenes and tools). In the same session, we compared unseen visually guided finger movements with a perceptually matched control condition in an event-related design (see Supplementary Fig. 1 online). Replicating Astafiev et al., we found a significant effect of finger movements in left (t12 = 4.5, P < 0.001) and right (t12 = 4.0, P < 0.005) EBA.

For each subject, a whole-brain contrast of finger movements versus control significantly (P < 0.00001, uncorrected) activated a bilateral temporal-occipital region (mean peak Talairach coordinates (x, y, z): left: −46, −65, −1; right: 53, −56, 0) that was close to the EBA (left: −45, −74, −3; right: 48, −68, 0). The peak of this action-related region (ARR), however, was significantly anterior to the EBA (left: t12 = 5.4, P < 0.001; right: t12 = 5.9, P < 0.001). Moreover, the spatial overlap4 of ARR with the EBA (at P < 0.0005, uncorrected) was only 14% (see Supplementary Fig. 2 online).

Note that the partial overlap of ARR and the EBA does not necessarily mean that the same neurons are involved in both motor actions and body perception. If this were the case, we would expect a positive voxel-by-voxel correlation between selectivity for bodies and action-related modulation. To test this, we defined for each subject the intersection of ARR and the EBA and calculated the correlation between the strength (as expressed by T values) of action-related activity compared to control, and body selectivity. The average correlation between these two measures was not statistically different from zero (r = 0.00, P = 0.96). This suggests that the region shared by ARR and the EBA contains interleaved but functionally independent neural populations.

To verify these findings, we scanned five subjects with an additional EBA localizer, using a contrast of body parts versus object parts. We replicated all of our key findings: a significant effect of pointing within the EBA (P < 0.05), a significantly anterior peak of ARR compared to EBA (P < 0.05), low spatial overlap of EBA and ARR (19%) and, if anything, a negative voxel-by-voxel correlation between action-related activity and body selectivity (r = −0.14, P = 0.08). In contrast, the correlation between selectivity for whole bodies and for body parts was significantly positive (r = 0.42, P < 0.05), showing that the absence of a correlation between action-related activity and body selectivity was not due to insufficient statistical power.

Thus, the temporal-occipital area that is involved in executing motor actions is distinct from the EBA. It may instead correspond to an area anterior to MT that is activated when subjects generate action-related words5. It also falls near the putative human homolog of MST, which represents visual motion in the periphery6,7. Further studies will be needed to determine the relationship between motor activity, action representation and visual motion-selective regions in lateral temporal cortex.

Note: Supplementary information is available on the Nature Neuroscience website (http://www.nature.com/natureneuroscience/).