The "closing-in" phenomenon refers to the tendency to copy near or overlap a model while performing figure-copying tasks. The mechanisms underlying the closing-in phenomenon have not been fully elucidated, and previous studies only investigated the mechanisms through neuropsychological tests. We investigated the neuroanatomical correlates of the closing-in phenomenon using voxel-based morphometry (VBM).

Thirty-eight patients diagnosed with probable Alzheimer's disease (AD) and 21 normal controls were included. All subjects underwent neuropsychological testing to diagnose dementia and magnetization prepared rapid acquisition gradient echo brain magnetic resonance imaging for the voxel-based statistical analysis. The subjects were asked to copy the modified Luria's alternating squares and triangles to quantify the closing-in phenomenon. We applied SPM8 for the VBM analysis to detect gray matter loss associated with the closing-in phenomenon.

The patients with probable AD showed a higher closing-in score than that of the normal control subjects ( p <0.0001). The VBM analysis revealed more parietal and temporal atrophy in the patients with AD than that in the normal control group. Moreover, atrophy of the orbito-frontal area was associated with the closing-in phenomenon.

The closing-in phenomenon is dysfunction while performing figure-copying tasks and is more common in patients with AD. The analysis of the orbito-frontal area, which is associated with inhibiting primitive reflexes, revealed that the closing-in phenomenon is an imitation behavior commonly observed in patients with frontal lobe damage.