A step toward cracking the code of how brains work.
Whether we’re paying attention to something we see can be discerned by monitoring the firings of specific groups of brain cells. Now, new work from Johns Hopkins shows that the same holds true for the sense of touch. The study brings researchers closer to understanding how animals’ thoughts and feelings affect their perception of external stimuli.
The results were published Nov. 25 in the journal PLoS Biology.
“There is so much information available in the world that we cannot process it all,” says Ernst Niebur, Ph.D., a professor of neuroscience in the Johns Hopkins University School of Medicine. “Many researchers believe the brain copes with this by immediately throwing away most of what we take in — that’s called selective attention. But we need to be certain that what is thrown away is really the irrelevant part. We investigated how our neurons do that.”
Niebur, a computational biologist, worked with Steven Hsiao, Ph.D., a professor of neuroscience in Johns Hopkins’ Zanvyl Krieger Mind/Brain Institute, who died in June, on the study. Hsiao’s assistant research scientist, Manuel Gomez-Ramirez, Ph.D., trained three rhesus monkeys to pay attention to either the orientation (vertical or horizontal) or the vibration rate (fast or slow) of a pencil-shaped object using their sense of touch. The monkeys learned to move their gaze to a location on a monitor screen corresponding to the right answer and were rewarded with drops of juice or water.
Gomez-Ramirez then monitored the activity of groups of neurons and figure out which were in charge of perceiving which property. When the monkeys were paying attention to the object’s orientation, he found, the neurons for that property fired more rapidly, and more synchronously, than did neurons for the vibration rate. That much was consistent with previous studies on selective attention in vision.
In addition, the research team found, the firing rate of the neurons for the property, and how much they synced up, predicted how well the monkey did on the task — whether it at to the correct location on the monitor. But synchronization was more important to performance than was firing rate.
The results are a step toward “cracking the neural code,” he says, an ambitious goal for which his research group continues to strive. “We’re looking for the neural code of internal thought processes,” he says. “It’s a very fundamental question.”
The National Institute of General Medical Sciences funded the study (grant: NIH IDeA P20GM103645).
Contact: Shawna Williams – Johns Hopkins Medicine
Source: Johns Hopkins Medicine press release
Image Source: The image is credited to geralt and is in the public domain
Original Research: Full open access research for “Temporal Correlation Mechanisms and Their Role in Feature Selection: A Single-Unit Study in Primate Somatosensory Cortex” by Manuel Gomez-Ramirez, Natalie K. Trzcinski, Stefan Mihalas, Ernst Niebur, and Steven S. Hsiao in PLOS Biology. Published online November 25 2014 doi:10.1371/journal.pbio.1002004
Temporal Correlation Mechanisms and Their Role in Feature Selection: A Single-Unit Study in Primate Somatosensory Cortex
Studies in vision show that attention enhances the firing rates of cells when it is directed towards their preferred stimulus feature. However, it is unknown whether other sensory systems employ this mechanism to mediate feature selection within their modalities. Moreover, whether feature-based attention modulates the correlated activity of a population is unclear. Indeed, temporal correlation codes such as spike-synchrony and spike-count correlations (rsc) are believed to play a role in stimulus selection by increasing the signal and reducing the noise in a population, respectively. Here, we investigate (1) whether feature-based attention biases the correlated activity between neurons when attention is directed towards their common preferred feature, (2) the interplay between spike-synchrony and rsc during feature selection, and (3) whether feature attention effects are common across the visual and tactile systems. Single-unit recordings were made in secondary somatosensory cortex of three non-human primates while animals engaged in tactile feature (orientation and frequency) and visual discrimination tasks. We found that both firing rate and spike-synchrony between neurons with similar feature selectivity were enhanced when attention was directed towards their preferred feature. However, attention effects on spike-synchrony were twice as large as those on firing rate, and had a tighter relationship with behavioral performance. Further, we observed increased rsc when attention was directed towards the visual modality (i.e., away from touch). These data suggest that similar feature selection mechanisms are employed in vision and touch, and that temporal correlation codes such as spike-synchrony play a role in mediating feature selection. We posit that feature-based selection operates by implementing multiple mechanisms that reduce the overall noise levels in the neural population and synchronize activity across subpopulations that encode the relevant features of sensory stimuli.
“Temporal Correlation Mechanisms and Their Role in Feature Selection: A Single-Unit Study in Primate Somatosensory Cortex” by Manuel Gomez-Ramirez, Natalie K. Trzcinski, Stefan Mihalas, Ernst Niebur, and Steven S. Hsiao in PLOS Biology. doi:10.1371/journal.pbio.1002004.