Seeing Is Believing, Indeed
-- by Joann Jovinelly
Understanding your physical place in the world from moment to moment (and how you got there) relies not on just one part of the brain, the hippocampus, as was previously suspected. As a new study shows, the memories and processes involved actually require several parts of the brain to work together in tandem.
The brain’s processes for creating new memories and putting that information into a context that we can use are very complex. Although the importance of the hippocampus in encoding and storing memory cannot be overstated, the surrounding area—chiefly the parahippocampal cortex or PHC—provides a crucial component in receiving and transferring that visual and spatial data.
In the study, which was published this month in Neuron, study author Rebecca Burwell, Ph.D., professor of psychology and neuroscience at Brown University, explains the new findings and how they might be useful for helping those with traumatic brain injuries and/or diseases like depression or schizophrenia.
The Expert Take
“Understanding how and where context is represented in the brain is important,” explains Burwell. “Context, or the place in which events occur, is the hallmark of episodic memory, but context is more than a place or a location. A room, for example, has a window, furniture, and other objects. You walk into a room and all that information helps you remember what happened there.”
Revealing just where and how the human brain makes connections regarding where it is within the context of surrounding objects will be invaluable when treating people with brain injuries or deficits in those regions.
“Individuals with schizophrenia and depression have trouble using context to plan actions or choose appropriate behaviors,” Burwell says. Her hope is that providing new information about how context is processed in the brain will help give rise to better treatments or details about how to further neurological rehabilitation.
Source and Method
In humans, the area of Burwell’s study focuses on the parahippocampal complex, but her research and testing is conducted on rats’ brains in the equivalent postrhinal cortex or POR.
And while scientists accept as fact that the POR, and subsequently the PHC, play a significant role in encoding spatial context, they previously believed that another area of the brain, the perirhinal cortex (PER), provided details about that context.
“The dogma is that this spatial and nonspatial information is segregated,” Burwell explains. “That is, until those streams of information are finally integrated by the hippocampus.”
Burwell, however, countered that conclusion and made it the center of her research, bolstered by the fact that recent studies also concluded that the PER and POR communicate directly with each other. Her conclusions proved accurate when rats with damage to the POR became confused about context. Burwell then theorized that the POR links objects to places to encode spatial context outside of the hippocampus.
“That’s what we think is happening in the POR,” she says. “It’s integrating information about place and information about objects to characterize the spatial layout of a local context.”
To prove her theory, Burwell and her team surgically inserted electrodes in the rats’ brains near the POR and had them perform a series of tasks, such as running a bowtie-shaped maze and choosing between two different projected images (objects). When the rats chose the “correct” object, they were rewarded.
During the experiment, neurons in the rats’ POR spiked when they looked at specific objects, such as the one associated with the reward. The experiments also revealed that the rats had a specific neuronal response for self-specific information, such as where objects were in relation to the rats' own placement.
While the brain and its inner-connectivity remains the final frontier in human medicine, researchers are consistently learning more about how the regions of the brain work together as well as independently.
Since we’ve learned that an increase in spatial information tends to increase gray matter in the hippocampus (London taxi drivers’ hippocampal regions increased in size after they learned to correctly navigate the city), it isn’t surprising that the new information gained is, in part, transferred from and processed by nearby regions.
There is abundant research about brain perception and activity. Several related studies show how the brain interprets visual clues, forms visual grids to navigate the world, and how surrounding contextual information is processed to help us define and make decisions about the evidence gathered.