The Organization of Abstract Brain Regions Like Sensory Brain Regions May Facilitate Information Flow
Post by Lani Cupo
The takeaway
Brain regions previously thought to be solely responsible for abstract processes, such as memory, can be organized like brain regions involved in sensory perception - detecting the world around us through our senses. This might indicate that information is being transferred between regions of the brain involved in sensory processing and abstract processes like memory.
What's the science?
Certain brain regions are known to be involved in external perception (e.g. vision), while others are associated with more abstract processes (e.g. memory). How information is communicated between these two types of processes is still an open question in neuroscience, especially since the neural code (or how the information is represented by neurons) for both systems is thought to be different. This week in Nature Neuroscience, Steel and colleagues use functional magnetic resonance imaging (fMRI) in humans to provide evidence for a way in which the perceptual and abstract processes may interact.
How did they do it?
Visual information is well known to have a retinotopic representation in the primary visual cortex, meaning that the neurons in this brain region are arranged corresponding to the region of the eye’s retina that they respond to. In this study, the authors first sought to determine whether the retinotopic organization of neurons exists not only in regions responsible for sensory processes as expected, but also in regions responsible for abstract processes. To do this, they acquired fMRI data from the entire cortex while participants viewed visual stimuli, to model populations of neurons associated with a retinotopic organization. They could also determine whether the neural responses to the stimulus that follow a retinotopic pattern were positive (greater than baseline) or negative (less than baseline). The authors also examined the ratio of positive to negative activations and identified brain regions outside of the visual cortex that showed a retinotopic pattern. Second, because they hypothesized that retinotopic activation outside of the visual cortex was related to memory, they had participants complete a memory task to test whether the ratio of positive to negative activity changed between the regions. Finally, the authors tested whether the same patterns of activity were observed in tasks more applicable to the real world that might activate both sensory and memory regions, by showing participants images of places that they were familiar with.
What did they find?
First, in addition to the expected retinotopic organization of the primary visual cortex (a key region for sensory perception), the authors found a retinotopic organization of neurons in higher-order regions of the brain involved in abstract cognitive processes. This is important because it has generally been theorized that only the primary visual cortex is organized corresponding to the retina. Specifically, during the perceptual task, brain activity was reduced in some memory areas (e.g. lateral parietal cortex), whereas in visual regions, activity increased in response to a stimulus. These findings suggested this inverse retinotopic organization may be associated with information transfer between perceptive and memory regions, so the authors next conducted imaging during a memory task. Consistent with this hypothesis, they observed opposite activation patterns, when comparing the perceptual and memory tasks. That is, they saw positive activations within retinotopic memory regions and negative activation in sensory regions. Finally, when they presented the participants with familiar scenes, the authors found the opposing interaction between sensory and memory regions persisted. This suggests that their findings are likely replicable in real-world scenarios and extend beyond the artificial and highly controlled laboratory settings of the first two experiments.
What's the impact?
This study provides additional evidence for a retinotopic organization of memory regions and suggests contrasting activity in memory and visual regions may be responsible for information transfer between sensory and higher-order regions. The findings further the understanding of how sensory and non-sensory brain regions communicate.
