Washington DC [US], August 5 : Researchers found that electrical activity in the brain is produced rhythmically by neurons.
What causes these rhythmic signals, also referred to as oscillations, is one of the unsolved questions in neuroscience. Simply recalling experiences has the power to trigger them, according to University of Arizona researchers, much more so than actually going through the experience.
Theta oscillations, which appear in the hippocampus region of the brain during activities like exploration, navigation, and sleep, were of particular interest to the researchers, whose findings were published in the journal Neuron.
The brain's capacity to recall the past is significantly influenced by the hippocampus.
According to Arne Ekstrom, professor of cognition and neural systems in the UArizona Department of Psychology and senior author of the study, it was previously thought that theta oscillations were more strongly influenced by the external environment. However, Ekstrom and his associates discovered that the primary source of theta activity is memory-related brain activity.
"Surprisingly, we found that theta oscillations in humans are more prevalent when someone is just remembering things, compared to experiencing events directly," said lead study author Sarah Seger, a graduate student in the Department of Neuroscience.
The results of the study could have implications for treating patients with brain damage and cognitive impairments, including patients who have experienced seizures, stroke and Parkinson's disease, Ekstrom said.
The memory could be used to create simulations from within the brain and drive theta oscillations, which could potentially lead to improvements in memory over time, he said.
According to Ekstrom, the study's findings may have an impact on how patients with cognitive impairments and brain damage are treated, including those who have had seizures, a stroke, or Parkinson's disease.
He suggested that memory could be used to stimulate the brain and drive theta oscillations, which might eventually result in improvements in memory.
Neurosurgeon Dr Brad Lega and research assistant Jennifer Kriegel from the University of Texas Southwestern Medical Centre in Dallas worked with researchers from the University of Arizona on the study. In order to prepare for epilepsy surgery, the centre was monitoring 13 patients, who were then recruited by the researchers.
Electrodes were implanted in the patient's brains as part of the monitoring in order to detect sporadic seizures. Theta oscillations were captured by the researchers in the hippocampus of the brain.
The patients took part in a virtual reality experiment where they were given a joystick to use to travel to stores in a computerised virtual city.
The virtual reality experiment was stopped when they reached their intended location. The participants were instructed to mentally navigate the route they had just travelled while also being asked to picture the starting point of their navigation.
Theta oscillations during initial navigation were then compared to participants' later recollections of the route by the researchers.
In comparison to oscillations that happened when participants were simply imagining the route, oscillations that occurred during the actual navigation process using the joystick were less frequent and shorter in duration.
The researchers, therefore, come to the conclusion that memory is a significant driver of theta oscillations in humans.
One way to compensate for impaired cognitive function is by using cognitive training and rehabilitation, Ekstrom said.
"Basically, you take a patient who has memory impairments, and you try to teach them to be better at memory," he said.
In the future, Ekstrom is planning to conduct this research in freely walking patients as opposed to patients in beds and find how freely navigating compares to memory with regard to brain oscillations.
"Being able to directly compare the oscillations that were present during the original experience, and during a later retrieval of that is a huge step forward in the field in terms of designing new experiments and understanding the neural basis of memory," Seger said.
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