Salient rhythms in the human insular cortex
Deep within the folds of the cerebral cortex is a region known as the insula, and one of its main functions is responding to stimuli that are surprising, or that deviate from expectations. In this study Dr. Darrell Haufler and colleagues from the laboratory of Dr. Denis Pare identify for the first time the neurophysiological activity that drives these salience signals. By combining intracranial recordings in epilepsy patients along with a virtual reality task, they show that surprising events produce a large increase in rhythmic "beta burst" activity in the insula. These beta bursts not only signal salient events in the insula, but also appear to coordinate with increases in rhythmic activity in other distant cortical areas, suggesting that the insula broadcasts its salience signals widely throughout the brain.
Protecting the temporal lobe with exercise
The medial temporal lobe (MTL) is one of the earliest brain regions impacted by Alzheimer’s disease. In a recent study, Dr. Neha Sinha and colleagues in the laboratory Dr. Mark Gluck show that exercise exerts a rehabilitative and protective effect on MTL function, resulting in networks that are more flexible and able to reconfigure in response to memory demands. These more flexible networks may underlie exercise-induced improvements on cognitive measures of generalization, which are sensitive to subtle changes in MTL function.
The essential role of acetylcholine in the striatum
The chemical messenger acetylcholine (ACh) is found throughout the brain, and one region where it is particularly important is the striatum, a part of the basal ganglia implicated in neurological disorders like Parkinson’s disease, dystonia, and Tourette syndrome. The laboratory of Dr. James Tepper studies the microcircuitry and function of striatal neurons, and in a recent study by PhD candidate Samet Kocaturk, they perform a comprehensive circuit analysis aimed at understanding how ACh-containing interneurons (CINs) contribute to striatal function. Using a combination of pharmacological, optogenetic, and neural recording approaches, they show that CIN activation recruits an intricate dual mechanism involving both pre- and postsynaptic ACh receptors on four distinct populations of striatal interneurons.
Strengthening memory with brain stimulation
Salient or emotional events produce strong memories. This depends in part on the amygdala, a brain region interconnected with other areas that support memory storage. Following a memorable experience, the amygdala exhibits rhythmic activity in the gamma frequency range (>40 Hz), which predicts the strength of subsequent memory. To test the importance of gamma, Dr. Drew Headley and colleagues developed a method to enhance or suppress gamma by tracking it in real-time and delivering stimulation during its rhythmic peaks or troughs. For the memory task, rats learned the location of a hidden cache of food, received one hour of stimulation, and then had their memory tested. They found that trough stimulation enhanced gamma and improved memory for the food location, while peak stimulation had the opposite effect. Dr. Headley is now adapting the technique to motor cortex with the goal of improving limb control following a stroke.