Evaluating reverse speech as a control task with language-related gamma activity on electrocorticography.

Reverse speech has often been used as a control task in brain-mapping studies of language utilizing various non-invasive modalities. The rationale is that reverse speech is comparable to forward speech in terms of auditory characteristics, while omitting the linguistic components. Thus, it may control for non-language auditory functions. This finds some support in fMRI studies indicating that reverse speech resulted in less blood-oxygen-level-dependent (BOLD) signal intensity in perisylvian regions than forward speech. We attempted to externally validate a reverse speech control task using intracranial electrocorticography (ECoG) in eight patients with intractable focal epilepsy. We studied adolescent and adult patients who underwent extraoperative ECoG prior to resective epilepsy surgery. All patients received an auditory language task during ECoG recording. Patients were presented 115 audible question stimuli, including 30 reverse speech trials. Reverse speech trials more strongly engaged bilateral superior temporal sites than did the corresponding forward speech trials. Forward speech trials elicited larger gamma-augmentation at frontal lobe sites not attributable to sensorimotor function. Other temporal and frontal sites of significant augmentation showed no significant difference between reverse and forward speech. Thus, we failed to validate reported evidence of weaker activation of temporal neocortices during reverse compared to forward speech. Superior temporal lobe engagement may indicate increased attention to reverse speech. Reverse speech does not appear to be a suitable task for the control of non-language auditory functions on ECoG.

High inter-reviewer variability of spike detection on intracranial EEG addressed by an automated multi-channel algorithm.

OBJECTIVE: The goal of this study was to determine the consistency of human reviewer spike detection and then develop a computer algorithm to make the intracranial spike detection process more objective and reliable. METHODS: Three human reviewers marked interictal spikes on samples of intracranial EEGs from 10 patients. The sensitivity, precision and agreement in channel ranking by activity were calculated between reviewers. A computer algorithm was developed to parallel the way human reviewers detect spikes by first identifying all potential spikes on each channel using frequency filtering and then block scaling all channels at the same time in order to exclude potential spikes that fall below an amplitude and slope threshold. Its performance was compared to the human reviewers on the same set of patients. RESULTS: Human reviewers showed surprisingly poor inter-reviewer agreement, but did broadly agree on the ranking of channels for spike activity. The computer algorithm performed as well as the human reviewers and did especially well at ranking channels from highest to lowest spike frequency. CONCLUSIONS: Our algorithm showed good agreement with the different human reviewers, even though they demonstrated different criteria for what constitutes a 'spike' and performed especially well at the clinically important task of ranking channels by spike activity. SIGNIFICANCE: An automated, objective method to detect interictal spikes on intracranial recordings will improve both research and the surgical management of epilepsy patients.

Transient shivering during Wada test provides insight into human thermoregulation.

PURPOSE: Some patients with pharmacoresistant epilepsy undergoing the Wada test experience transient shivering. The purpose of this study was to investigate various clinical and radiographic characteristics of these individuals to delineate underlying mechanisms of this phenomenon. METHODS: A systematic review of prospectively collected information on patients undergoing the Wada test was performed. All demographic, clinical, and radiographic information was obtained and reviewed by the appropriate expert in the field; statistical analysis was performed to determine the predictors of transient shivering. RESULTS: A total of 120 consecutive carotid artery injections in 59 patients were included in the study. Shivering was observed in 46% of the patients, and it was not significantly affected by gender, age, location of epileptogenic zone, brain lesion on magnetic resonance imaging (MRI), side of the first injection, duration of the hemiparesis, or excess slow wave activity on electroencephalography (EEG). However, shivering was more likely to follow sodium amobarbital injection if there was no filling of the posterior circulation on cerebral angiogram. DISCUSSION: Transient shivering during the Wada test is common. A transient but selective functional lesion of the anterior hypothalamus produced by the effects of sodium amobarbital may result in disinhibition of the posterior hypothalamus and other brainstem thermoregulatory centers, thereby inducing transient shivering.