This paper is the product of a collaboration between Birmingham’s School of Psychology and Nottingham’s Physics department using novel multimodal brain imaging techniques to better understand an often overlooked phase of brain function.
The post stimulus undershoot is a component of the fMRI signal that occurs after an external stimulus has ceased or a task has finished. The real-life issue of the undershoot is that this response occurs after the perception of a stimulus or the performance of the task has finished.
Usually brain function is studied using signal responses that occur during the task, but there are brain responses that are related to the offset of the task as well, although their function is poorly understood. Researchers think this signal relates to the transition from the active brain state back to the resting state. It represents part of the mechanism for the re-setting of the whole sensory cortex back into its internal rhythm. So the undershoot may say something about how the brain stops doing things, in contrast to most imaging signals which indicate how it starts, or continues, doing things.
Up until now this signal has not been used to study how the brain works because its origin was uncertain. This work provides compelling evidence that the post-stimulus undershoot is a measure of neuronal activity rather than just changes in the brains blood flow.
The exact functional role of the post-stimulus undershoot is not known but the work suggests that this signal might help the brain make the transition from processing stimuli back to their internal thoughts in different ways. The team hope that this work will enable them to map a kind of brain function that up to now couldn’t be studied before, and open up a new window of time in which they can look at what the brain is doing.
The abstract of the paper is available on the PNAS early release page.