Abstracts

Rationale: The aim of this project was to compare the localization of language, motor and sensory cortices sites using three different methods; intracranial evoked response potentials (iERP), gamma frequency analysis using the SIGFRIED procedure (Bruner et al. 2009; Schalk et al., 2008) and direct cortical stimulation (DCS) mapping . Each technique was performed on adult epilepsy patients with subdural electrodes implanted over sensory-motor and language cortex for localization of intractable epilepsy. Methods: In the first method the intracranial data were recorded during two tasks, a language mismatch negativity paradigm (MMN) and a somatosensory paradigm. In the MMN paradigm, the patient passively listened to a stream of sounds consisting of frequent and infrequent stimuli which were either phonemes, matched non-phonemes or matched tones. In the somatosensory paradigm patients were presented with medial nerve stimulation on the hand. Data collected were then analyzed off line by computing iERPs in the time domain . The second method, was an on-line analysis of the signal in the gamma frequency domain using the SIGFRIED procedure, while the patient performed language and sensory-motor tasks. The third method was an on-line causal mapping protocol which consisted of a systematic evaluation of the language and sensory-motor functions while the patient received DCS. Results: The results revealed good spatial overlap for iERPs, frequency analysis and DCS for both the language sites and sensorimotor sites. We also noted that iERPs showed more diffuse activations than was observed using the SIGFRIED analysis. Conclusions: In conclusion both iERP and SIGFRIED analysis may be useful in identifying essential functional cortical sites, although the distribution may be more widespread compared with DCS mapping.