Roles of left and right Dorsolateral Prefrontal Cortex during spatial and cognitive processing

The dorsolateral prefrontal cortex (DLPFC) is important to cognitive and
spatial control, such that one key function of the DLPFC is thought to be the
inhibition against distracting information in order to guide attention to
another location in space. In a typical laboratory task to assess this
function, the anti-saccade task, subjects must look away from a visual stimulus
and generate an accurate eye-movement to another location. It is thought that
the DLPFC is crucial to inhibiting a reflexive eye-movement towards the
stimulus, and generating the voluntary anti-saccade. However, whether each
hemisphere (left/right) contributes similarly to these functions, whether each
hemisphere processes predominantly one side of space, or whether there are
distinct lateralizations (where only one hemisphere is critical) needs to be
assessed. This is important, because the DLPFC is a brain region investigated
in many brain stimulation studies of cognitive control, attention, and spatial
memory processes, but researchers typically only examine the influence of brain
stimulation on left or right DLPFC, but not both.

We aim to better dissociate the roles of the left and right DLPFC in cognitive
control and spatial processing, using a commonly used saccadic eye-movement
task. Future studies will then have better information with regards to the
influence of brain stimulation on left or right DLPFC.

A counter-balanced design, where we will apply 40s of inhibitory transcranial
magnetic stimulation (continuous theta-burst stimulation) cTBS to the right or
left DLPFC (or vertex control region) prior to performing the task.

Single-pulse transcranial magnetic stimulation (TMS) and continuous theta burst
stimulation (cTBS).

Each participant will receive no direct benefit from participating in the
study, but will receive a compensatory (financial) incentive. Transcranial
magnetic stimulation (TMS) is a widely used non-invasive brain stimulation
technique, based on the principle of electromagnetic induction. During
stimulation the participant will likely hear the clicks of the TMS pulses and
experience stimulation of nerves and muscles of the head. The most common side
effect is a light transient headache (2-4% occurrence). A severe headache is
uncommon (0.3-0.5% occurrence). In TMS studies of patient populations (e.g.
epilepsy) or that exceeded the standard protocols (e.g. in intensity or
frequency) epileptic seizures have been reported in rare cases. In the current
study all participants will be stimulated with protocols that fall within the
safety guidelines. All subjects are screened for their relevant medical history
and other TMS safety aspects (e.g. presence of metal parts in the head). In
summary, because the risk and burden associated with participation can be
considered negligible-to-minimal, we do not expect serious adverse events
during the project.