"Seeing" electroencephalogram through the skull: imaging prefrontal cortex with fast optical signal

Area of Science:

• Neuroscience
• Biomedical Engineering
• Cognitive Science

Background:

• Near-infrared spectroscopy (NIRS) is an imaging technique sensitive to brain hemodynamics and neuronal activity.
• Measuring fast optical signals (FOS) noninvasively is challenging due to low signal-to-noise ratio.
• Detectability of FOS has been debated in scientific literature.

Purpose of the Study:

• To reliably detect FOS noninvasively in human subjects.
• To investigate the correlation between FOS and electroencephalogram (EEG) signals during a cognitive task.
• To explore the potential of NIRS for cortical mapping of cognitive processes.

Main Methods:

• NIRS probes placed over prefrontal cortex in 11 individuals during a Go-NoGo task.
• Concurrent electroencephalogram (EEG) recordings were obtained.
• Independent component analysis (ICA) used for artifact removal and signal analysis.

Main Results:

• Reliable detection of FOS achieved in all subjects, with significant correlation to EEG (p < 10(-8)).
• Event-related optical signals (EROS) showed similarity to event-related potential (ERP) components, including an "optical N200".
• The "optical N200" component coincided with the N200 ERP, differentiating targets from non-targets and correlating with reaction time.

Conclusions:

• FOS components directly reflect electrical brain processes, evidenced by single-trial correlations with EEG.
• NIRS provides a highly localized and cost-effective tool for neuroimaging.
• Data suggest early prefrontal cortex involvement in rapid object recognition and support NIRS for cognitive process mapping.