Wouldn’t it be more efficient and economical to find the obstreperous brain circuit (or lack thereof) associated with losing one’s vehicle in a parking lot, rather than to hunt for a circuit which facilitates finding said vehicle? Regardless, researchers at the University of California – San Francisco (UCSF) have discovered a connection in the brains of mice that prompts their attention to the salient features of a new environment.
The connection originates in the prefrontal cortex and links it to the hippocampus, an example of the brain’s higher cognitive regions orchestrating operations in distant brain sites.
“This circuit is a gateway to understanding how the brain allows the prefrontal cortex to exert top-down regulation of other parts of the brain,” says senior author Dr. Vikaas Sohal, MD, PhD, in a statement. “It’s a type of long-range, inhibitory pathway connecting two brain regions, a pathway previously unknown.”
The prefrontal cortex (PFC) controls executive functions, such as attention, planning, and decision making. The hippocampus processes spatial information and commits it to memory, for use in navigating the environment. According to lead author Dr. Ruchi Malik, PhD, as the newly discovered circuit attends to important features of the environment, it ignores distracting sensory stimuli.
Malik gives the example of a parking lot as a context in which the PFC exerts that kind of top-down control over the hippocampus. “To remember where you parked, the PFC would tell the hippocampus to selectively pay attention to landmarks, and then recall and seek out those landmarks when you return,” explained Malik.
This circuit is unique in its complexity of function needed to accomplish the task of focusing attention. It directs activity in specific microcircuits of the hippocampus by inhibiting signals that subdue the microcircuits. Thus, the PFC signal to the hippocampus is clear, directing it to attend to salient environmental features.
The team put mice into a small arena in which there were a few objects. While exploring the arena, the mice inspected the objects for a minute or two, then moved on. The monitored the brains of the mice, noting that the signals between the two brain regions synchronized. When a mouse passed a particular object again, the pertinent signals within the hippocampus were refined and enhanced.
“There was this dialogue happening; the hippocampus was mapping the locations of objects in space, and the PFC was instructing the hippocampus on the relevance of each location,” says Malik.
Data indicated which neurons were firing at a given time and identified where the mouse was at that moment. It confirms that brain activity changes as the mouse approaches or investigates an object that the PFC has already deemed important. These changes indicate that the hippocampus maps the environment.
Malik believes that dysfunction in this pathway may underlie cognitive issues related to attention or memory, such as dementia, ADHD, or psychiatric disorders.
“To operate in a complex environment, to go look for food or rewards and then come back, you need to pay attention to specific stimuli and arrange them in space in a precise way,” she said. “The filtering job of this circuit is absolutely essential.”
The research is published in the journal Cell.