Selective effects of a brain tumor on the metric representation of the hand: a pre- versus post-surgery comparison

Abstract

Body representation disorders are complex, varied, striking, and very disabling in most cases. Deficits of body representation have been described after lesions to multimodal and sensorimotor cortical areas. A few studies have reported the effects of tumors on the representation of the body, but little is known about the changes after tumor resection. Moreover, the impact of brain lesions on the hand size representation has been investigated in few clinical cases. Hands are of special importance, as no other body part has the ability for movement and interaction with the environment that the hands have, and we use them for a multitude of daily activities. Studies with clinical population can add further knowledge into the way hands are represented. Here, we report a single case study of a patient (AM) who was an expert bodybuilder and underwent a surgery to remove a glioblastoma in the left posterior prefrontal and precentral cortex at the level of the hand's motor region. Pre- (20 days) and post- (4 months) surgery assessment did not show any motor or cognitive impairments. A hand localization task was used, before and after surgery (12 months), to measure possible changes of the metric representation of his right hand. Results showed a post-surgery modulation of the typically distorted hand representation, with an overall accuracy improvement, especially on width dimension. These findings support the direct involvement of sensorimotor areas in the implicit representation of the body size and its relevance on defining specific size representation dimensions.

Keywords: Body representation; Brain tumor; Hand size; Localization task; Metric representation; Sensorimotor areas.

Fig. 1

Patient AM’s T1-weighted magnetic resonance imaging scans before and after surgery. A T1-weighted (SPGR) magnetic resonance imaging scan in native space showing lesion location in the left posterior prefrontal and precentral cortex at the level of the hand region. Top right panel shows a 3D reconstruction of the lesion volume. Top left, bottom left and bottom right pictures represent coronal, transverse and sagittal slices centered on the lesion volume, respectively. B Transverse and sagittal views of the post-surgery MR scan (with T1 enhancement after gadolinium administration) in native space, coregistered to the pre-surgery scan

Fig. 2

Hand localization task. Modified from Mora et al. (2021)

Fig. 3

Distortion of widths and lengths. Representation of perceived underestimation and overestimation (%) of finger lengths (A), hand dorsum (B), hand width (C) and wrist width (D), for the right hand. Error bars represent the standard error of the mean. * Significant differences after correction for multiple comparisons

Fig. 4

Cartographic maps for the real and perceived representation of the right hand. Black dotted lines represent the real size of the hands. The light gray dots represent all AM’s pointing responses from which averaged representation is calculated (solid lines)