Investigation of Oscillations Underlying Human Cognitive and Affective Processing Using Intracranial EEG

Purpose: To investigate the electrophysiological correlates of human cognition and affective processing. Participants: Drug-resistant epilepsy patients undergoing epilepsy surgery cortical mapping with continuous electrocorticography (ECoG) with intracranial electrodes. Procedures (methods): Participants will perform computer-based cognitive and affective processing tasks during routine long-term monitoring. Intracranial EEG will be collected during the task

Oscillations in different frequency bands like theta, alpha, beta, gamma and high gamma are thought to underlie processing of cognitive and emotional information. For example, theta (3 - 7 Hz) and alpha (8 - 12 Hz) oscillations are known to underlie working memory as well as attentional processing. Theta oscillations are known to differentiate emotional and neutral stimuli while gamma oscillations (30 - 50 Hz) are known to underlie rapid integration of information. The fact that these oscillations are also disrupted in neuropsychiatric disorders underline the importance of these oscillations.

A lot of our understanding of these oscillations come from non invasive methods in humans like electroencephalography (EEG), magnetoencephalography (MEG) and invasive methods in animal models. However, EEG and MEG measure oscillations that are generated by collective firing of large cortical patches thereby losing spatial resolution. Also activity from deeper structures like amygdala and hippocampus cannot be picked up in these modalities. Animal models often suffer from the poor translation of behavior from animals to humans and vice versa. Intracranial EEG or Electrocorticography (ECoG) helps overcome the drawbacks described above.

Studies using ECoG have become widespread and have been helpful in elucidating the functional roles of different brain regions in cognition and emotion. The investigators aim to utilize these established procedures to study the role of oscillations recorded from different brain regions in cognition and emotion.

Patients with medically refractory epilepsy undergo long-term invasive monitoring for surgical resection planning. Electrodes are implanted subdurally over seizure focus to identify seizure onset zone and patients are often in the epilepsy monitoring unit at the Neuroscience hospital for approximately a week. During this period, intracranial EEG is constantly acquired for clinical investigation. The investigators plan to recruit these patients while they undergo long-term monitoring to leverage the rare access to direct brain recordings and study the role of oscillations in cognitive and affective processing. Patients who provide informed consent to participate in the study will perform computer based cognitive and emotional processing tasks.

Eligibility Criteria:
Inclusion Criteria:

1. History of medically intractable epilepsy
2. Capable of giving informed consent
3. Aged 18 - 80 years, either sex

Exclusion Criteria:

1. Major systemic illness
2. Severe cognitive impairment defined as mini-mental state examination of less than 20
3. Severe psychiatric illness
4. Excessive use of alcohol or other substances