Lesion-network mapping in task-dependent frequencies uncovers remote consequences of focal damage

The brain consists of a multiplicity of networks with massively interacting nodes. Disruption of a node following brain damage can result in both short- and long-distance functional abnormalities, affecting even intact brain regions remote from the site of lesion (termed 'diaschisis'). Diaschisis has been well described previously, and structural and functional connectivity have been related to clinical findings. However, the mechanistic and neurophysiological properties of this remote loss of function, its temporal and spectral dynamics, and its impact on the whole brain remain to be elucidated. In this study, we used high-density electroencephalography (EEG) to detect and characterize function- and frequency-dependent transcallosal diaschisis in a single-case of visual agnosia who has a perceptual deficit in object and face recognition following a focal lesion in the right posterior temporal cortex. Scalp EEG activity was evoked by images of intact and parametrically increased scrambled objects. SilenceMap, an algorithm developed for the location of reduced power (i.e., regions of silence), was used to estimate the slope of shape-selective EEG responses at levels of object scrambling, with structural and functional MRI serving as the ground truth for the lesion and diaschisis. The functional deficit, manifest as a significant reduction in the slope of EEG object shape sensitivity, was observed in the lesioned right ventral cortex and right dorsal cortex across most of the frequency bands ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>></mml:mo> <mml:mn>4</mml:mn> <mml:mo> </mml:mo> <mml:mo> </mml:mo> <mml:mi>H</mml:mi> <mml:mi>z</mml:mi></mml:mrow> </mml:math> ). This reduction in EEG slope was accompanied by contralesional diaschisis in the homotopic left ventral and left dorsal cortex but only in the Theta band ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>4</mml:mn> <mml:mtext>​</mml:mtext> <mml:mo>-</mml:mo> <mml:mtext>​</mml:mtext> <mml:mn>8</mml:mn> <mml:mo></mml:mo> <mml:mi>H</mml:mi> <mml:mi>z</mml:mi></mml:mrow> </mml:math> ). This noninvasive approach both elucidates the neural correlates of diaschisis and confirms the viability of this approach in identifying neurological abnormality, perhaps offering a path toward precision medicine.