Methods
If you have questions about the method or if you want to sign up to participate in our studies, please contact the Egner lab via phone (919.684.1034) or email (egner.laboratory@gmail.com).
Behavioral Experiments
Since our goal is to understand how the brain produces adaptive thoughts and actions, the most fundamental data we base our theories on are behavioral: we design psychological experiments and compare participants’ response times and error rates across different conditions to infer what kind of conditions require how much processing time, whether different cognitive processes can be carried out in parallel or must occur sequentially, and so forth. Sometimes we are able formalize our theories in mathematical terms and use computational modeling to try to simulate and predict human performance. Once we have established a robust behavioral signature of a particular cognitive computation, we can try to elucidate the brain mechanisms underlying that computation using fMRI and TMS.
Functional Magnetic Resonance Imaging (fMRI)
While behavioral experiments allow us to make many inferences about the cognitive architecture of the mind, they do not reveal the neural implementation of those cognitive processes. To relate behavior to the brain, we have participants perform our cognitive experiments in an MRI scanner. Using fMRI allows us to noninvasively measure local changes in blood-oxygenation levels in the brain, an indirect measure of neural activity, as a function of the cognitive operations the participants have to carry out in different experimental conditions. We can then relate the neural activation patterns in different brain structures to the cognitive requirements of our tasks. This approach results in correlational data: we can tell which brain areas become activated by, or harbor information about, different stimuli or cognitive states. However, these data do not allow us to draw causal inferences about the necessity of a given brain region for a specific cognitive computation. To move from correlational to causal inferences, we sometimes use a noninvasive brain stimulation technique called TMS.
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The MRI scanners we use are located at the Duke University Hospital, and they are operated and maintained through the Brain Imaging and Analysis Center (BIAC) at Duke University. More information regarding fMRI studies in general and participation can be found on their research website.
Transcranial Magnetic Stimulation (TMS)
TMS is a technique that allows us to noninvasively induce small electric currents in someone’s brain. Since neurons communicate with each other via electric currents, this technique can mimic, disrupt, or even enhance the function of the stimulated neurons. TMS involves rapidly switching on and off an electric current in a plastic-enclosed wire coil that is placed over a person's head. The electric field in the coil produces a perpendicular magnetic field, which in turn induces a small electric current in the brain area close to the coil. By inducing these small current, and depending on the exact frequency and amplitude of the stimulation, one can either suppress or enhance the functioning of the underlying brain region for a short period of time. This allows us to assess the causal role that this brain region might play in a particular cognitive computation: if suppressing the activity in a specific brain region leads to impaired task performance, we can infer that the region in question is necessary for normal task performance.
Our TMS studies are carried out in Egner Lab space in the Division of Brain Stimulation and Neurophysiology in Duke's Department of Psychiatry and Behavioral Sciences.