Stability and plasticity of functional brain networks after hemispherectomy: implications for consciousness research

Laterality and hemispheric specialization of self-face recognition

Inspired by the pioneering work of Eran Zaidel beginning in the early 1970's on the role of the two cerebral hemispheres of the human brain in self-related cognition, we review research on self-face recognition from a laterality perspective. The self-face is an important proxy of the self, and self-face recognition has been used as an indicator of self-awareness more broadly. Over the last half century, behavioral and neurological data, along with over two decades of neuroimaging research evidence have accumulated on this topic, generally concluding a right-hemisphere dominance for self-face recognition. In this review, we briefly revisit the pioneering roots of this work by Sperry, Zaidel & Zaidel, and focus on the important body of neuroimaging literature on self-face recognition it has inspired. We conclude with a brief discussion of current models of self-related processing and future directions for research in this area.

Postoperative seizure and developmental outcomes of children with hemimegalencephaly and drug-resistant epilepsy

OBJECTIVE

To evaluate seizure and developmental outcomes in the short and long term in children with hemimegalencephaly (HMEG) after surgery.

METHODS

This is a cohort study of 36 children who underwent surgery for HMEG were followed up for at least 1 year postoperatively. The Griffiths Mental Development Scales, Ages and Stages Questionnaire version 3, and Peabody Developmental Motor Scales were used to assess development.

RESULTS

The median postoperative follow-up duration was 2.7 (1.0-5.0) years, and median age at surgery was 1.9 years (5.8 months-5.9 years). At the last follow-up, 83% of children were seizure-free. the predicted probability of being seizure-free three years after surgery was 79%. The proportion of patients who were moderate to severe delay declined from 97% preoperatively to 76% at least 1 year after surgery. Catch-up, stabilization, and regression of developmental quotient (DQ) was observed in 41%, 35%, and 24% of children 3 months after surgery, respectively. The corresponding proportions during long-term follow-up were 40%, 33%, and 27%, respectively. Change of DQ shortly after surgery was negatively correlated with age at seizure onset and age at surgery. The long-term DQ was positively correlated with the preoperative DQ. Long-term change of DQ was positively correlated with change of DQ shortly after surgery.

CONCLUSIONS

Most of patients with HMEG could achieve seizure free after surgery. After surgery, the proportion of catch-up, stabilization, and regression in both short- and long-term DQ was approximately 40%, 35%, and 25%, respectively. The change of DQ shortly after surgery may be a predictor for long-term developmental change.

Independent and unified consciousness co-existence in commissurotomy cases

Independent hemispheric consciousness was observed following complete commissurotomy under controlled laboratory conditions that restricted stimulus input and response output to a single hemisphere. Hemispheric specialization was investigated in this way. Consciousness of the self was tested directly as well and found to be represented in each of the hemispheres. Unified consciousness was evidenced in unaltered personality, character, humor, and past knowledge (autobiographical and knowledge of the world). Intact cortico-subcortical projections to intact subcortical regions are offered as explanation for why both unified and independent are possible in the same brain.

Large-scale resculpting of cortical circuits in children after surgical resection

Despite the relative successes in the surgical treatment of pharmacoresistant epilepsy, there is rather little research on the neural (re)organization that potentially subserves behavioral compensation. Here, we examined the post-surgical functional connectivity (FC) in children and adolescents who have undergone unilateral cortical resection and, yet, display remarkably normal behavior. Conventionally, FC has been investigated in terms of the mean correlation of the BOLD time courses extracted from different brain regions. Here, we demonstrated the value of segregating the voxel-wise relationships into mutually exclusive populations that were either positively or negatively correlated. While, relative to controls, the positive correlations were largely normal, negative correlations among networks were increased. Together, our results point to reorganization in the contralesional hemisphere, possibly suggesting competition for cortical territory due to the demand for representation of function. Conceivably, the ubiquitous negative correlations enable the differentiation of function in the reduced cortical volume following a unilateral resection.