Inhibiting the Development of Threat Memories with TMS
Post by Megan McCullough
The takeaway
Decreasing activity in the primary sensory cortex through transcranial magnetic stimulation interferes with the formation and consolidation of threat memories in humans.
What's the science?
The ability to predict events based on past experiences is important as it allows us a degree of self-protection. However, some individuals are impacted by memories in a way that negatively affects their behavior and wellbeing. Previous studies have primarily used drug administration to study human threat memory. Because drugs cannot be administered only to specific brain areas, it does not allow researchers to study the specific regions involved in developing threat memories. Previous research has implicated the sensory cortices in the development of threat memories, but it is still unclear whether they are a necessary brain region for threat memory development. This week in Biological Psychiatry, Ojala and colleagues studied the relationship of the primary sensory cortex (S1) and human threat memory using transcranial magnetic stimulation (TMS), a technique that induces excitability changes in neurons in specific brain regions.
How did they do it?
First, all participants underwent functional magnetic resonance imaging (fMRI) while fingers of their left hand were stimulated to localize the S1 in each individual’s brain. Participants then received TMS to the area identified by the fMRI. The authors used continuous theta-burst TMS to decrease activity in the primary sensory cortices of the participants. TMS was used because it is non-invasive and circuit-specific. Each trial of the experimental task involved electric pulses being administered to the fingers of the left hand while participants fixated on a cross on a screen and indicated with a button the stimulus pattern they perceived. Participants in the control group received the TMS to the left side of the brain from the stimulation while participants in the experimental group received the TMS to the right side of the brain (which contains the S1 corresponding to the fingers of the stimulated left hand). Right after the administration of the TMS, participants underwent threat conditioning; an electric shock was delivered intermittently during the experimental task. The next day, memory retention of the threat of the electric shock was assessed by measuring fear-potentiated startle during trials of the task.
What did they find?
The authors found a decreased fear response during the trials after fear conditioning in participants in the experimental TMS group. This shows that decreasing activity in the sensory cortices in the side of the brain where the stimulation to the fingers was represented, affected the formation of memories of the threat of the painful shock. This implicates the S1 in the consolidation of threat memories in humans. It also illustrates the usefulness of TMS in studying relationships between specific brain regions and the formation of fear memories.
What's the impact?
This study found that the primary sensory cortices are involved in the process of forming and consolidating memories associated with events that invoke feelings of fear. The study also shows that TMS can be an effective technique for interfering with the development of fear memories. This finding has clinical relevance as TMS is a potential treatment for individuals adversely affected by threat memories such as those with anxiety disorders.