Control of Brain Signals

Volitional Control of Cortical Brain Signals

Overview: This work is the bulk of my Ph.D. research under Dr. Eberhard Fetz at the University of Washington. As this is the main work entering my thesis and a few publications I will need to be brief regarding the results of the experiments. If you would like further information on these projects, please feel free to email me.

Brief Details:

  • Developed novel experimental paradigms to enhance volitional control of cortical signals
  • Derived mathematical correlates between cortical brain signals and behavior
  • Designed wireless motion capture and reward system for tracking and analysis in freely moving animals
  • Constructed and implanted neural hardware for long term cortical recordings
  • Mentored multiple students on related projects concerning local field potentials and behavior

Background

Brain computer interfaces(BCI) have huge implications for improving the lives of people with motor dysfunction. While a BCI can refer to any system that aids interaction between the brain and technology, we tend to focus on motor action related BCIs - or systems that are targeted towards people with motor deficits. This often takes the form of interfacing a computer cursor or motorized prosthetic with specially decoded brain signals that allow for someone to interact with their world again.

Operant Conditioning is a paradigm used to explore new BCI technologies in animal models. A BCI system requires high fidelity brain signals which in turn call for more invasive techniques when exploring cutting edge BCI research. In my work, we use operant conditioning to reward non-human subjects for modulations in spontaneous brain activity. By rewarding specific patterns of activity, the subject can learn to volitionally modulate this signal. Through this principle, I have trained subjects to modulate both single neurons and field potentials in the brain.

Operand Conditioning of Single Neuron Firing Rate in Motor Cortex

One of the earliest BCI systems used the firing rate of single neurons in the motor cortex to control a voltage meter. In these studies, the subject was rewarded for modulating neuron activity with food pellets, demonstrating volitional control in a traditional operant conditioning paradigm. Current BCI technologies that use single neuron activity rely on advanced control algorithms, but the basic principles rely on the subject being able to determine which thoughts or actions can drive the external device. The exploration of the control space can be aided by auditory, visual, or reinforcement based feedback. Additionally, a longer period of time to explore the space may lead to more robust control of the system. Initial experiments of volitional control of single neurons focused on the motor cortex, where the control paradigm targets neurons related to overt physical movements. Other cortical areas are becoming prime targets for BCI based interventions which may not have as well defined control spaces. Research topics I have explored in this area:

Volitional Control of Motor Cortex Field Potentials in Free Behavior

Local field potentials arise from the collective activity of cellular and extracellular processes in the brain. LFP signals are reemerging as an alternative to single neuron activity in BCI technologies, due to increases in accessibility, signal longevity, and new signal processing techniques. The signal power of specific frequencies in the LFP signal are related to a range of behavioral activities. While this relationship between LFP and behavior is not as well understood as that of single neurons, the power of these specific frequency bands can be used to control BCI devices. Traditional studies examine the ability of an subject to control the power in a given frequency band in restrained environments. In this work I aimed to demonstrate volitional control of motor cortex LFP in a freely behaving animal.

Through this work I was able to clearly observe the animal's voluntary control of beta signal activity (13-30Hz) for extended periods of time. The bulk of this work will be included within a paper focusing on the free-behavior technologies required for the study.

Volitional Control of PreFrontal Cortex Field Potentials

Volitional control of local field potentials in the prefrontal cortex is an additional unexplored control signal for brain computer interface technologies. The prefrontal cortex has been shown to modulate with the integration of sensory information and the control of executive behavior. The prefrontal cortex outputs directly to the premotor cortex which outputs to the motor cortex . All three of these sites may be ideal locations for BCI interventions due to their involvement in volitional motor control. However, the PFC may offer distinct advantages over motor areas. In my current work I am studing the efficacy of volitional control of LFP in prefrontal cortex while simultaneously recording LFP in premotor and motor cortices. These results will also lend insight to whether volitional control of LFP is a local or system wide phenomenon.