Collaborative Research: US-German Research Proposal: optimization of human cortical stimulation

Long used for cortical mapping, electrical stimulation of human cortex is an emerging strategy for brain-computer interface and rehabilitation strategies. The mechanisms of how stimulation induces change in function are poorly understood but even less is known about surface (as opposed to intracortical) stimulation, even though the former is the clinically used modality.  Even the distribution of current within cortex is unknown.  As higher resolution arrays become possibilities in the clinical setting, it is increasingly important to understand whether current can be distributed to functionally relevant cortex, or even the limits of predicting where the current is distributed. Studies of non-invasive stimulation, such as transcranial magnetic stimulation, are leading to the development of methods, including finite element models, that make predictions about the distribution of current.

In this Collaborative, US-German project, we seek to apply these methods to the case of brain surface cortical stimulation. We will validate these models using surface and sub-surface arrays in an animal model, including novel geometric designs of the arrays. We will apply these methods to human data in patients with indwelling electrodes. Using novel patterns of stimulation (at low strengths), we will validate models of surface stimulation that seek to distribute current to specific cortical locations, such as the depths of sulci. These computational models will allow for accurate design and implementation of future cortical arrays.  Specifically: 1. Animal models of cortical stimulation will be developed to maximize stimulation of regions of interest. 2. These models will be validated across a variety of inter-electrode distances and geometries (based on the model results) in sheep studies. 3. Conventional human cortical stimulation will be modeled with varying spatial patterns of stimulation proposed and 4. These models will be validated with surface stimulation and recording in patients with implanted electrodes.

Intellectual Merit:

This will represent one of the first attempts to characterize the distribution of cortical stimulation in clinical situations, or animal models that mimic the clinical situation. The study of current distribution into deeper sulci, as the result of different spatial electrode parameters, and validation of these finite element models are all novel, particularly in the case of direct cortical stimulation.

Broader Impacts:

The development of tools to assess cortical stimulation will have immediate and substantial implications for stimulation uses such as mapping for neurosurgical procedures, emerging research using cortical stimulation for stroke rehabilitation, and closed-loop sensorimotor brain-computer interface. This will directly impact a large number of patients suffering from stroke, paralysis and other neurological disorders. The collaboration between the four groups will build on pre-existing relationships and strengthen interdisciplinary work in the field of cortical stimulation and allow for increased sharing of information into their respective fields (e.g., neurosurgical information into electrical engineering fields and vice versa). The collaboration with the University of Freiburg group will additionally build on pre-exisiting joint projects and leverage technical expertise in electrode development.  The education of undergraduate students, graduate students, and post-doctoral fellows will advance the field. Undergraduate work will target underrepresented groups and this work will also expose K-12 students to brain stimulation and brain mapping fields. 
 

Principal Investigator(s)
Research Lab