The clinical and anatomical heterogeneity of environmental dependency phenomena

Following damage to the frontal lobes, the observation of patients presenting with environmental dependency syndrome (EDS), particularly with its two main components--grasping and imitation behavior, provides a unique opportunity to gain new insights into the neural bases of human autonomy and free-will. In the present study, thirty-nine patients with frontal lobe dysfunction [21 with progressive supranuclear palsy (PSP), and 18 with the behavioral variant of frontotemporal dementia, (bvFTD)] were tested for environmental dependency phenomena and underwent neuropsychological evaluation and T1-weighted 3D brain MRI. We correlated scores obtained by assessing grasping, imitation and utilization behaviors with both neuropsychological executive test performance and grey matter density on MRI using Voxel-Based Morphometry (VBM). This study confirms the high frequency of two environmental dependency phenomena- grasping and imitation- in patients with frontal lobe syndrome (34/39 patients) and the rarity of utilization behavior (2/39). The grasping score was significantly and positively correlated with those obtained in all executive tests except the Stroop test, while the imitation score was not. In the VBM study, while the grasping score was correlated with grey matter density in the right superior frontal gyrus and both inferior temporal gyri, the imitation score was correlated with changes in the right insula, left medial frontal gyrus and left precuneus. Environmental dependency is associated with the dysfunction of a frontoparietal network. Within this large network, grasping and imitation behaviors can be dissociated from both neuropsychological and anatomical standpoints, underlining the clinical and anatomical heterogeneity of environmental dependency phenomena.