Summary: Whether we are consciously aware of seeing a familiar face and object or not, our brains actively notice. A new study sheds light on the nature of conscious perception.
Source: Cell Press.
When people see an image of a person they recognize — the famous tennis player Roger Federer or actress Halle Berry, for instance–particular cells light up in the brain. Now, researchers reporting in Current Biology on September 21 have found that those cells light up even when a person sees a familiar face or object but fails to notice it. The only difference in that case is that the neural activity is weaker and delayed in comparison to what happens when an observer consciously registers and can recall having seen a particular image.
The findings offer new insight into the nature of conscious perception, the researchers say.
“Our study finds that a ‘Roger Federer cell’ can also become active when its owner fails to notice the image of Roger Federer rapidly flickering by in a stream of other images,” says Florian Mormann of University of Bonn Medical Center in Germany. “Thus, we find that there is highly abstract information present in neuronal activity that is inaccessible to conscious experience.”
The researchers made the discovery by recording the activity of 2,735 individual neurons in 21 neurosurgical patients implanted with brain electrodes for epilepsy monitoring. They took advantage of a phenomenon known as attentional blink in which people who attend to two familiar images in quick succession will often fail to notice the second. The experimental setup allowed the researchers to directly compare the neural response to seen and unseen presentations of the very same image.
As expected, study participants often failed to notice the presence of a second target image, especially when it was presented soon after a first target image. The researchers found that the corresponding neurons fired either way. However, there was an observable difference in the strength and timing of that neural response.
“Studying the activity of individual neurons in awake, behaving humans was key to picking up weak but informative signals from individual neurons during nonconscious perception, particularly in regions further down the processing stream, which are impossible to measure with conventional tools,” Mormann says. “We were quite surprised to see that timing of neuronal responses is indicative of whether participants report having seen the image or not.”
The findings weigh in on theoretical debates about the nature of human consciousness, the researchers say. For instance, it hasn’t been clear whether consciousness is an all-or-nothing phenomenon or a matter of degrees. The researchers say the observation that neuronal firing occurs in both cases, but differently, argues in favor of consciousness as a more nuanced, graded phenomenon.
The researchers say they’d now like to explore how the activity of individual neurons in one part of the brain is related to activity in other brain areas and how those connections relate to conscious awareness.
Funding: This research was supported by the Volkswagen Foundation, the German Research Council, and the Swiss National Science Foundation.
Source: Joseph Caputo – Cell Press
Image Source: NeuroscienceNews.com image is credited to Reber et al.
Original Research: Full open access research for “Single-Neuron Correlates of Conscious Perception in the Human Medial Temporal Lobe” by Thomas P. Reber, Jennifer Faber, Johannes Niediek, Jan Boström, Christian E. Elger, and Florian Mormann in Curren Biology. Published online September 21 2017 doi:h10.1016/j.cub.2017.08.025
Single-Neuron Correlates of Conscious Perception in the Human Medial Temporal Lobe
•Neurons fire in response to their preferred stimulus also in absence of awareness
•Neuronal responses to unseen versus seen stimuli are delayed and more dispersed
•Firing rates to seen versus unseen stimuli are increased
•These correlates of awareness are strongest in anterior regions of the MTL
The neuronal mechanisms giving rise to conscious perception remain largely elusive. It is known that the strength of single-neuron activity correlates with conscious perception, especially in anterior regions of the ventral pathway in non-human primates and in the human medial temporal lobe (MTL). It is unclear, however, whether single-neuron correlates of conscious perception are characterized solely by the magnitude of neuronal responses, and whether the correlates of perception are equally prominent across different regions of the human MTL. While recording from 2,735 neurons in 21 neurosurgical patients during 40 experimental sessions, we created experimental conditions in which otherwise identical visual stimuli are sometimes seen and sometimes not detected at all by means of the attentional blink, i.e., the phenomenon that the second of two target stimuli in close succession often goes unnoticed to conscious perception. Remarkably, responses to unseen versus seen stimuli were delayed and temporally more dispersed, in addition to being attenuated in firing rate. This finding suggests precise timing of neuronal responses as a novel candidate physiological marker of conscious perception. In addition, we found modulation of neuronal response timing and strength in response to seen versus unseen stimuli to increase along an anatomical gradient from the posterior to the anterior MTL. Our results thus map out the neuronal correlates of conscious perception in the human MTL both in time and in space.
“Single-Neuron Correlates of Conscious Perception in the Human Medial Temporal Lobe” by Thomas P. Reber, Jennifer Faber, Johannes Niediek, Jan Boström, Christian E. Elger, and Florian Mormann in Curren Biology. Published online September 21 2017 doi:h10.1016/j.cub.2017.08.025