Neural Activity Elicited by a Cognitive Task can be Detected in Single-Trials with Simultaneous Intracerebral EEG-fMRI Recordings

Recent studies have shown that it is feasible to record simultaneously intracerebral EEG (icEEG) and functional magnetic resonance imaging (fMRI) in patients with epilepsy. While it has mainly been used to explore the hemodynamic changes associated with epileptic spikes, this approach could also provide new insight into human cognition. However, the first step is to ensure that cognitive EEG components, that have lower amplitudes than epileptic spikes, can be appropriately detected under fMRI. We compared the high frequency activities (HFA, 50-150 Hz) elicited by a reading task in icEEG- only and subsequent icEEG-fMRI in the same patients (n = 3), implanted with depth electrodes. Comparable responses were obtained, with 71% of the recording sites that responded during the icEEG- only session also responding during the icEEG- fMRI session. For all the remaining sites, nearby clusters (distant of 7 mm or less) also demonstrated significant HFA increase during the icEEG- fMRI session. Significant HFA increases were also observable at the single-trial level in icEEG- fMRI recordings. Our results show that low-amplitude icEEG signal components such as cognitive-induced HFAs can be reliably recorded with simultaneous fMRI. This paves the way for the use of icEEG- fMRI to address various fundamental and clinical issues, notably the identification of the neural correlates of the BOLD signal.