Methods

Computer-based behavioral assessments

We develop novel behavioral tasks--combining demands across several domains--to probe cognitive processes and performance.

For instance, we may have participants remember one or multiple items over a delay of several seconds. Then, while they’re maintaining that information, have them perform some kind of intervening perceptual, attentional, or action task, before being tested on their memory of the initial information. The goal is to use behavioral perturbation that can both manipulate the brain activity associated with maintenance and also read out properties of the maintained information. Conversely, we use memory performance to gauge the influence of those intervening demands.

In addition to traditional measures of accuracy and response time, at both of these stages we use sensitive measures like mouse-tracking and computational modelling, to extract nuanced aspects of performance.

We also combine this sort of cognitive manipulation with (a) fMRI measurements of brain activity to explain behavior and to test theoretical predictions about how the brain achieves cognition, as well as (b) causal perturbations of brain function (specifically with focal transcranial magnetic stimulation), to probe the functional role of fMRI activations and their impacts on behavior. We use these convergent methods in an iterative way to continuously inform and update our cognitive and neural models.

Functional Magnetic Resonance Imaging (fMRI)

We combine behavioral task manipulations with fMRI measurements of brain activity. We use fMRI to explain behavior and to test theoretical predications about how the brain achieves cognition.

We use multivariate analyses of fMRI activity patterns to assess how information is represented in the brain, and to characterize how mental representations of information are impacted by complex task demands 

We use network measures of functional connectivity to assess how large scale brain organization facilitates cognition, and to measure flexible changes in brain network configuration in response to task demands.

We use measures of brain activity and connectivity to functionally guide brain stimulation. We use fMRI-guided TMS over target regions of interest to causally test their contributions to behavior.

Transcranial Magnetic Stimulation (TMS)

We use perturbations of brain function, via focal transcranial magnetic stimulation (TMS), to support causal inference about the roles of particular brain regions. We probe the necessity of targeted brain regions to performance, assessing the functional role of activations we measure with fMRI.

TMS delivers brief pulses on the scalp--via quickly changing magnetic gradients--which can temporarily perturb the electrical activity in the stimulated region (and in connected regions). TMS can be delivered in a range of frequencies, intensities, and temporal patterns, which can produce distinct impacts on the stimulated region of cortex. TMS can consequently have disruptive or facilitative impacts on behavior, depending on the stimulation parameters (as well as on characteristics of the individual, the context, and the stimulated region).

“Offline” TMS can be delivered before or after participants perform one of our cognitive tasks. This form of repetitive TMS is designed to perturb neural activity for a period of time that outlasts the duration of the stimulation itself (i.e., up to ~an hour). For instance, participants may perform a task after the stimulation has ceased, but during a period when it should continue to affect neural activity (as well as cognitive processes that depend on that activity). 

We use offline theta-burst TMS over fMRI-guided targets of interest to compare the causal contributions of multiple regions. We also stimulate based on connectivity patterns, to target subcortical regions that would be otherwise out of reach of the superficial stimulation. And we use theta-burst protocols that are thought to have both excitatory and inhibitory impacts on processing

We also use "online" TMS--which is delivered while participants perform a cognitive task--for temporally precise assessments of the targeted region’s contributions to particular cognitive processes. This sort of TMS can be delivered in single pulses, or in brief trains of rhythmic pulses at frequencies that may underlie oscillatory neural processes for distinct cognitive functions. 

We use stereotactic neuronavigation to position the TMS coil over our anatomical or functional target of interest, and we use EMG to calibrate TMS intensity based on each participant’s sensitivity.