ASSR as a Biomarker

• Analyzed EEG data from 100+ participants to investigate gamma-band ASSR as a potential biomarker for prediction of clinical response to rTMS in treatment resistant depression (TRD).
• Applied advanced signal processing techniques (ERSP, ITC) and statistical analysis to uncover neural-cognitive associations in healthy and clinical populations.

Advisors:

• Dr. Fidel Vila-Rodriguez - University of British Columbia, Vancouver, Canada
• Dr Colleen Brenner – University of Loma Linda, California, USA
• Dr. Reza Shalbaf - ICSS, Tehran, Iran

Research Abstract

Gamma-band oscillations may underlie sensory and cognitive processes and could be reflected by the auditory steady-state response (ASSR) from electroencephalogram (EEG) recordings. There is little knowledge about the association between cognitive performance and gamma-band (40-Hz) ASSR in healthy volunteers (HV) and treatment-resistant depression (TRD) patients. Our study aims to obtain 40-Hz ASSR at scalp electrodes and neural sources and explore its possible association with cognitive performance for healthy and patient samples, as well as its possible biomarker role in the prediction of treatment response to repetitive transcranial magnetic stimulation (rTMS) in TRD. EEG data of 43 HVs and 62 TRD patients were recorded during auditory stimulation. Cognitive functions were tested for different domains, including verbal learning, verbal fluency, attentional shifting, working memory, inhibition, and premorbid IQ. Two ASSR variables, inter-trial coherence (ITC) and event-related spectral perturbation (ERSP), were computed. The association between ASSR variables and cognitive scores was assessed by Pearson‘s correlations at electrode and source levels. For HVs, attentional shifting, verbal learning and memory, as well as premorbid IQ were significantly associated with ERSP at neural sources, primarily located at the left occipital, parietal, and temporal regions. At these neural sources, working memory was significantly associated with ITC. For TRD patients, shifting attention was significantly associated with ERSP at the left frontal, parietal, and temporal regions, as well as verbal learning and memory were associated with ERSP and ITC at central electrodes. Also, non-responders to rTMS treatment had a deficit in 40Hz-ERSP relative to responders. Our results suggest the presence of a widely distributed network of 40-Hz ASSR neural generators, located at cortical and subcortical regions beyond the primary auditory cortex (A1). The analyses imply that 40-Hz ASSR might be a biomarker for the specific domains of cognitive performance at particular cortical neural sources and a biomarker for the prediction of the treatment response to rTMS.