Laterality of seizure onset and the simple reaction time: revamping the Poffenberger's paradigm for seizure surgery

Abstract

Background: Crossed-uncrossed differentials (CUDs) are viewed as surrogates for interhemispheric transfer time (IHTT). Not uncommonly CUDs assume statistically significant negative values (inverted CUDs). This raises doubts of the accepted interpretation of CUDs, i.e. intra- and inter-hemispheric routings of signals in uncrossed and crossed responses, respectively.

Method: Based on the evidence supporting directionality in callosal traffic, data are provided indicating that callosal transfers exclusively involve non-dominant responses and such transfers are modality non-specific. The evidence also indicates that neural handedness corresponds to behavioral only in a statistical manner and the former remains unchanged regardless of the subject's life experience.

Results: The neurally dominant side is the side that is directly connected to the major hemisphere (command center). The connection of the non-dominant side to the command center is via the corpus callosum; therefore, a delay occurs in the reaction time of all non-dominant effectors, corresponding to IHTT. Accordingly, negative CUDs indicate a mismatch of neural and behavioral (avowed) handedness of the subject. This group comprises a minority of 15–20% of the population.

Conclusion: Comparing the response time of symmetrically located effector is a robust way of lateralizing a person's major hemisphere. The latter is also the site of initiation of seizures, as the minor hemisphere is bereft of independent motor activity. Sensory signals arising from the nondominant side of the body traverse the callosum before reaching the major hemisphere. Searching for ipsilateral somatosensory evoked potentials provides another approach in lateralizing the non-dominant side of the body (ipsilateral to the major hemisphere). Practical uses of a conceptually revamped Poffenberger paradigm in neurosurgery are briefly reviewed.

Keywords:

• NEURAL HANDEDNESS
• BEHAVIORAL HANDEDNESS
• EPILEPSY
• MAJOR HEMISPHERE
• MINOR HEMISPHERE
• REACTION TIME
• POFFENBERGER PARADIGM