Search

To determine clinically ictal direct current (DC) shifts that can be identified by a time constant (TC) of 2 s and to delineate different types of DC shifts by different attenuation patterns between TC of 10 s and 2 s.Twenty-one patients who underwent subdural electrode implantation for epilepsy surgery were investigated. For habitual seizures, we compared (1) the peak amplitude and (2) peak latency of the earliest ictal DC shifts between TC of 10 s and 2 s. Cluster and logistic regression analyses were performed based on the attenuation rate of amplitude and peak latency with TC 10 s.Ictal DC shifts in 120 seizures were analyzed; 89.1% of which were appropriately depicted even by a TC of 2 s. Cluster and logistic regression analyses revealed two types of ictal DC shift. Namely, a rapid development pattern was defined as the ictal DC shifts with a shorter peak latency and they also showed smaller attenuation rate of amplitude (73/120 seizures). Slow development pattern was defined as the ictal DC shifts with crosscurrent of a rapid development pattern, i.e., a longer peak latency and larger attenuation rate of amplitude (47/120 seizures). Focal cortical dysplasia (FCD) 1A tended to show a rapid development pattern (22/29 seizures) and FCD2A tended to show a slow development pattern (13 /18 seizures), indicating there might be some correlations between two types of ictal DC shift and certain pathologies.Ictal DC shifts, especially rapid development pattern, can be recorded and identified by the AC amplifiers of TC of 2 s which is widely used in many institutes compared to that of TC of 10 s. Two types of ictal DC shifts were identified with possibility of corresponding pathology.Ictal DC shifts can be distinguished by their attenuation patterns.

Objective In order to evaluate the clinical utility even under general anesthesia, the present study aimed to clarify the effect of anesthesia on the cortico–cortical evoked potentials (CCEPs). Methods We analyzed 14 patients’ data in monitoring the integrity of the dorsal language pathway by using CCEPs both under general anesthesia with propofol and remifentanil and awake condition, with the main aim of clarifying the effect of anesthesia on the distribution and waveform of CCEPs. Results The distribution of larger CCEP response sites, including the locus of the maximum CCEP response site, was marginally affected by anesthesia. With regard to similarity of waveforms, the mean waveform correlation coefficient indicated a strong agreement. CCEP N1 amplitude increased by an average of 25.8% from general anesthesia to waking, except three patients. CCEP N1 latencies had no correlation in changes between the two conditions. Conclusions We demonstrated that the distribution of larger CCEP responses was marginally affected by anesthesia and that the CCEP N1 amplitude had tendency to increase from general anesthesia to the awake condition. Significance The CCEP method provides the efficiency of intraoperative monitoring for dorsal language white matter pathway even under general anesthesia.

Introduction Human brain operates with oscillatory activity in different frequency bands. For example, mu rhythm is well known as an idling rhythm observed in the central area related to motor function. We observed some rhythmic pattern in the averaged waveforms in the CCEP investigation (called “oscillatory response” here), which is originally a method to trace connectivity by single electrical pulse stimulation. We report on the frequency and distribution of the oscillatory responses in CCEP. Methods Subjects are 5 intractable epilepsy patients who underwent chronic implantation of subdural electrodes for presurgical evaluation. Written informed consents were obtained from all subjects. Single-pulse stimuli (0.3 ms, 8–10 mA, alternating polarity, 30 × 2 trials) were applied through two adjacent electrodes (52.8 ± 15.3 stimulus sites per patient). CCEP was recorded from subdural electrodes (105.2 ± 31.8 electrodes per patient) placed on the lateral and medial aspect of the cerebral hemisphere. Lateral fronto-parietal area was covered in all subjects. An oscillatory response in CCEP was detected by visual inspection on the averaged waveform according to the following criteria; (1) it has at least two pairs of peak and trough spaced equally, (2) it can be overlapped with other evoked responses (typical N1/ N2 response). If more than one rhythms with different frequencies were observed in the same electrode, we counted the largest one in amplitude. Results Totally, 2362 oscillatory responses (7.9%) were detected in 29891 observations in 5 subjects, including 443 alpha-band responses (7.5–13.5 Hz), 312 beta-band responses (13.5–30 Hz) and 1505 theta-band responses (3.5–7.5 Hz). Theta rhythm was observed predominantly in the temporal lobe including the basal temporal area (the occurrence rate was 12.45%). Alpha rhythm was observed more often in the parietal lobe including the postcentral gyrus (the occurrence rate was 4.57%), while beta rhythm was often observed around precentral gyrus (the occurrence rate was 1.98%). The frequency of the resting rhythmic activity was equal to that of oscillatory CCEP response in the alpha band in the postcentral gyrus in all subjects. This alpha activity was considered as mu rhythm in all the 3 subjects who performed a hand grasping task. Conclusion Single pulse electrical stimulation evoked oscillatory CCEP responses preferentially in the temporal lobe and the perirolandic area. The correspondence of frequency between the oscillatory response and mu rhythm implies the phase resetting of the physiological oscillation by exogenous input. This unique oscillatory CCEP may help to map these functionally important cortical regions.

Cortico-cortical evoked potential (CCEP) has been widely used to probe brain network. Typically CCEP waveform consists of two negative potentials, N1 (peak: 10–50 ms) and N2 (peak: 100–500 ms). We, however, occasionally encounter atypical responses, such as those with prolonged N1 peak latency. We attempt to classify these atypical patterns and clarify their anatomical distribution. We retrospectively reviewed CCEP responses in two patients with intractable focal epilepsy, in whom CCEPs were obtained bystimulating all the implanted subdural electrodes (IRB#443). We classified CCEP into 6 groups based upon the N1 and N2 peak latencies; IA: N1 (10–50 ms), N2 (100–500 ms), IB: N1 (10–50 ms), N2: (50–100 ms), IIA: N1 (50–100 ms), N2: (100–500 ms), IIB: N1 (50–100 ms) without definite N2, III: mirror CCEP response with positive peaks, IV: N1 (100–500 ms) without definite N2. Atypical CCEP responses (IIA, IIB, III, IV) accounted for 16.0% among all the recording. They mostly distributed in the temporal lobe. There was a tendency of preferred locations for each pattern; IIB in the lateral temporal region and frontal operculum, III in the superior temporal gyrus and mesial temporal region, IV in the temporal pole. Further case accumulation is warranted to verify the results, which helps understand the significance of CCEP for presurgical evaluation.

Objective: In order to establish a new intraoperative monitoring for preservation of subcortical language pathways, we applied technique of cortico-cortical evoked potentials (CCEP) during brain surgery. Methods: Subjects were 17 patients with brain tumors located close to the arcuate fasciculus (AF) in the language-dominant left hemisphere. Af- ter craniotomy, electrodes were placed over frontal and parieto-temporal perisylvian areas. Single-pulse stimuli were applied to several pairs of electrodes in the frontal area to record CCEP from the parieto-temporal area. Under general anesthesia, the anterior perisylvian language area (AL) was first defined by CCEP connectivity patterns, and also by presurgical neuroimaging findings. We then monitored the integrity of the language network by stimulating AL and recording CCEPs from the posterior peri- sylvian language area (PL) consecutively during both general anesthesia and awake condition. In the awake condition, language assessment with batteries was also sequentially performed throughout surgical procedures. To confirm language function in AL, high-frequency electrical stimulation (ES) was performed during awake craniotomy in nine patients, who had neither cognitive impairment nor aphasia preoperatively. Results: In all, the CCEP connectivity pattern delineated perisylvian lan- guage network between AL and PL even under general anesthesia. CCEP amplitude declined in two patients (≤32%) during surgical procedures. Two patients had transient language impairment postoperatively. One patient who showed 32% decrease of CCEP amplitude presented phonemic para- phasia during and after operation. Another patient who did not showed decrease of CCEP amplitude developed language impairment immediately after surgery because of brain edema. Language function recovered within a few months in both patients. In all, CCEP monitoring successfully prevented persistent language impairment. In all nine patients who were awakened fully, high-frequency ES confirmed language impairment at AL. Conclusions: Although further accumulated cases will be warranted for establishing the sensitivity and specificity, intraoperative CCEP delineated the perisylvian or dorsal language network and would be useful for online monitoring of subcortical language pathways.