An international team of scientists says that it has made a significant advance in the understanding of conscious perception by discerning how single neurons in the human brain react to perceived and non-perceived images.
Dr Rodrigo Quian Quiroga, a bioengineer at the University of Leicester who is spearheading the research, says that the study is opening new possibilities of exploring a hitherto relatively unchartered scientific area.
"There has been much interest in recent years in consciousness, which is considered by many as one of the major scientific challenges to be solved, or at least addressed in a scientific -rather than just philosophical- way," Dr Quian Quiroga said.
While revealing the process involved in the study, Dr Quian Quiroga said: "Recordings were done in epileptic patients candidates of curative surgery in which intracranial electrodes are implanted to establish the location of the epileptic focus and evaluate the potential outcome of the surgery. Patients usually stay for 1 or 2 weeks in the guard and this gives us the extraordinary opportunity to perform experiments and study how neurons in the human brain respond to different perceptual and behavioural tasks."
"In this particular study we showed pictures in a computer screen very briefly, at the threshold of conscious recognition. Subjects had to report whether they recognized or not the particular picture showed in each trial. The key point is that, since the pictures are shown very briefly, for exactly the same visual input sometimes the subjects reported recognizing the picture and sometimes not recognizing it. Then we could ask whether the neurons fire according to the subjects' conscious perception or the actual visual inputs," he said.
As to what the study showed, the researcher added: "We found that the neurons we recorded responded to the conscious perception in an 'all-or-none' way by dramatically changing their firing rate only when the pictures were recognized. For example, a neuron in the hippocampus of one patient fired very strongly to a picture of the patient's brother when recognized and remained completely silent when it was not, another neuron behaved in the same manner with pictures of the World Trade Centre, etc."
"Interestingly, based on the firing of these neurons it was possible to predict far above chance whether a picture was recognized or not. Another interesting observation is that a picture flashed very briefly generated nearly the same response -if recognized- as when shown for much longer periods of time. This means that a single snapshot as brief as 33 ms was sufficient to trigger strong neuronal responses far outlasting the stimulus presentation, signalling the conscious perception of the picture shown," he added.
Dr Quian Quiroga said that the study, published in the Proceedings of the National Academy of Sciences (PNAS), had important implications.
According to him, potential applications of this discovery include the development of such Neural Prosthetic devices for paralysed patients or amputees as will read commands directly from the brain and transmit them to bionic devices.
The researcher sees the work showing that it is possible to read signals from the brain as a good step forward in this direction.
However, certain clinical and ethical issues still pose a great challenge before the application of Neural Prosthetic devices in humans, especially because it will involve an invasive surgery that will have to be justified by a clear improvement for the patient before it could be undertaken.
But still, Dr Quian Quiroga says that the new discovery also has far-reaching implications for the treatment of patients with pathologies involving the hippocampal formation, such as epilepsy, Alzheimers and schizophrenia and for further understanding of how perceptions and memories are represented in the brain.