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

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.

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