Behavioral and Functional Brain Activity Alterations Induced by TMS Coils with Different Spatial Distributions

Abstract

Previous investigation of cognitive processes using transcranial magnetic stimulation (TMS) have explored the response to different stimulation parameters such as frequency and coil location. In this study, we attempt to add another parameter by exploiting the spatial profiles of TMS coils to infer regional information concerning reward-related behavior.We used different TMS coils to modulate activity in the prefrontal cortex (PFC) and examined resulting changes in behavior and associated brain activity. More specifically, we used the Figure-8 coil to stimulate a portion of the dorsolateral PFC (DLPFC) and the H-Coil to stimulate a larger volume within the lateral PFC (LPFC). Healthy human volunteers completed behavioral questionnaires (n=29) or performed a reward-related decision-making fMRI task (n=21) immediately before and after acute high-frequency stimulation (10 Hz) with either a Figure-8 coil, H-Coil, or a sham coil.Stimulation was found to induce behavioral changes as well as changes in brain activation in key nodes of the reward network. Right LPFC, but not right DLPFC or sham, stimulation was found to induce changes in both behavioral scores and brain activation in key nodes of the reward system.In conclusion, this study supports the role of the right LPFC in reward-related behavior and suggest that the pathways through which the observed effects were generated are located outside the area of the DLPFC that is traditionally targeted with TMS. These results demonstrate the use of TMS coils with different spatial profiles as an informative tool to investigate anatomical and functional correlates of behavior.Significance StatementWhen trying to associate cognitive function with brain anatomy, probing with neuromodulation has emerged as a useful approach. One can modulate brain activity with techniques such as TMS and examine the effect on behavior. Yet, hypotheses often associate behavior with relatively large brain areas which is inefficient, requiring many experimental groups to provide useful information. Here, we describe an approach using TMS coils with different field distributions to achieve a similar goal with reduced time and simplified resources. Our results indicated a pattern that differed between a focal coil (Figure-8) coil and a wider/deeper coil (H-Coil). Future studies may localize the origin within the frontal cortex that drives these effects, and thereby further establish the association between structure and function.

Unresolved Issues Associated with Transcranial Magnetic Stimulation (TMS) Treatment of Chronic Tinnitus

“…However, as described in the section above, different brands and configurations of coils might cause variations in the stimulation parameters that can affect treatment outcomes. While figure-of-eight coils stimulate a somewhat narrow region of cortex, newer H-coils can stimulate a wider and deeper neural area, and should be studied in tinnitus populations [35]. For a review of TMS coil types, see Ilmoniemi et al [36].…”