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Reliability of neural activity as an assay of cognitive state (in collaboration with Lucas Parra). The ability to faithfully measure human cognitive state would find immediate application in multiple settings (e.g. the control room and navigation environments). Our central hypothesis is that cognitive state modulates the reliability of sensory processing, as measured by the correlation between stimulus features and neural activity. Preliminary data from our group indicates that attentional state and task difficulty modulate the reliability of EEG. These findings were enabled by the development of a new regression technique for measuring the reliability of neural responses. A related hypothesis is that being actively engaged with a stimulus leads to fundamentally different neural responses than when passively observing it.   The goal of this work is to increase our understanding of how the brain represents its environment in real-world settings, while also advancing the state-of-the-art in brain-state monitoring. This research is funded by the Army Research Laboratory.

 

EEG-informed Transcranial Electrical Stimulation (in collaboration with Marom Bikson). To demonstrate causal relationships between brain and behavior, investigators would like to guide brain stimulation using measurements of neural activity. Particularly promising in this context are EEG and transcranial electrical stimulation (TES), as they are linked by a reciprocity principle which, despite being known for decades, has not led to a formalism for relating EEG recordings to optimal stimulation parameters.  We have derived a closed-form expression for the TES configuration that targets the sources of recorded EEG, without making any assumptions about source location or distribution. We also derive a duality between TES targeting and EEG source localization, and demonstrate that in cases where source localization fails, so does the proposed targeting.  Our focus now is to validate these findings in human experiments.    This work could allows brain scientists and clinicians to rationally target the sources of observed EEG and thus overcome a major obstacle to the realization of closed-loop brain stimulation.

 

Augmenting cerebral oxygenation with laser stimulation (in collaboration with Greg Dmochowski and Hanli Liu).   The brain makes up only 5% of the body’s mass, yet consumes over 20% of the its energy.  In order to metabolize glucose and generate ATP, the brain requires a steady supply of oxygen in its blood supply. Deficits in cerebral blood flow and oxygenation are associated with ischemic stroke and several neurodegenerative disorders.   We are investigating the use of near-infrared light to increase cerebral oxygenation.  The experiments involve applying low levels of coherent light (i.e., lasers) to the brain transcranially.     This work is funded by a CUNY Junior Faculty Research Award.

 

Multi-scale brain imaging  (collaboration with Anthony Norcia, Adam Kohn, and Jeffrey Schall).  The electroencephalogram (EEG) is arguably the most widely collected neural signal. Despite the fact that it was discovered almost 90 years ago, we still do not have a good understanding of how the EEG relates to cellular-level signaling such as action potentials.  We are probing the relationship between the EEG and spiking by simultaneously measuring intracranial multi-unit activity and extracranial EEG.  Advanced regression techniques are then used to decode the relationship between these two neural signals.

 

Ultrasonic neuromodulation (collaboration with Elisa Konofagou)Existing techniques for stimulating the brain using electromagnetic fields are limited in spatial resolution and penetration depth.    The human skull greatly attenuates low-frequency electric fields, resulting in weak stimulation of the cortex.  This has arguably led to the variable and generally insufficient results in TMS and TDCS research.  In principle, ultrasound waves can overcome these limitations: ultrasonic waves have already been shown to be focused through the human skull in high-intensity applications for neurosurgery.   The same focusing can be applied in a low-intensity regime to achieve targeted neuromodulation of cortical and subcortical brain structures.  We are investigating ultrasound as a tool to interrogate brain circuits, beginning with experiments in rodents.  The effects of the stimulation are monitored using electrophysiological recordings.