Neurons respond strongly to stream of familiar images
As the study of neuroscience becomes increasingly prevalent in modern society, we are just beginning to understand the many complexities of the brain, namely its highly adaptable nature. Researchers from the Center for the Neural Basis of Cognition (CNBC), a joint Carnegie Mellon and University of Pittsburgh project, have explored this aspect of the brain through their research involving neuron response to rapid sequences of images.
Carl Olson, a professor of biological sciences at Carnegie Mellon and a member of the CNBC; Travis Meyer, a research associate of neuroscience at the CNBC; and Christopher Walker and Raymond Cho of the department of psychiatry at the University of Pittsburgh examined how neurons react to familiar and unfamiliar images presented in rapid succession.
The researchers showed animal and human subjects rapid sequences of familiar and unfamiliar images and monitored the electrical responses of various individual neurons in the inferotemporal cortex, a section of the brain that is crucial for recognizing objects, to determine whether the inferotemporal cortex neurons followed the rapidly changing images better when the images were familiar or unfamiliar.
The researchers ultimately found that subjects’ neurons responded much more strongly and selectively when shown familiar images in rapid succession than when shown unfamiliar images in rapid succession. The research also showed that the strong response for familiar images was more prevalent in inhibitory neurons — neurons that calm the brain and restore balance — than in excitatory neurons — neurons that stimulate the brain. “You wouldn’t expect there to be such deep changes in the brain from simply making things familiar,” said Olson in a university press release. “We think this may be a mechanism the brain uses to track a rapidly changing visual environment.”
In previous research, it was established that a subject’s neurons respond more strongly when shown a single unfamiliar image than when shown a single familiar image. The CNBC study, however, was focused on rapid series of images — not a singular image — which explains the difference in the results.
The concept that repeated viewing of an image causes neurons to respond to it in a weaker manner is called the familiarity effect. In the CNBC study, researchers noted that this effect could be beneficial, not detrimental. The researchers explained that familiarization occurs in the form of a truncation. In other words, the neuron response is not weaker overall; it is simply truncated early for familiar images. The study suggests that this truncation could make the neuron response more selective and could allow the neurons to be more prepared to respond to ensuing images.
Overall, the researchers concluded that image familiarization improved the dynamics of the neuron response in the inferotemporal cortex. They suggest that each image triggers a specific subset of neurons that respond to certain aspects of that image and that the enhanced response for familiar images could be part of the brain’s mechanism for monitoring visual environments that are swiftly changing. They also note that the presence of an enhanced response in excitatory neurons is important because it suggests that the enhanced effect could be transmitted from the inferotemporal cortex to other areas of the brain.
The research was funded by the National Institutes of Health’s National Eye Institute and the National Institute of Mental Health, as well as the Pennsylvania Department of Health’s Commonwealth Universal Research Enhancement Program. The study, titled “Image familiarization sharpens response dynamics of neurons in inferotemporal cortex,” is published online by Nature Neuroscience.