How chronic pain disrupts short term memory

A group of Portuguese researchers from IBMC and FMUP at the University of Porto has found the reason why patients with chronic pain often suffer from impaired short –term memory. The study, to be published in the Journal of Neuroscience, shows how persistent pain disrupts the flow of information between two brain regions crucial to retain temporary memories.

Chronic pain suffers often complain of short term memory’s problems. The neural mechanisms why this occurs are however not understood. Recent studies in animals showed that pain can disturb several cognitive processes as well as change the brain pathways for how we think and feel. Of the many cognitive disturbances observed the most important include problems in spatial memory, recognition memory, attention and even emotional and non-emotional decisions.

In the new article the team of researchers from the University of Porto led by Vasco Gallardo describes in a rat model of neuropathic pain how a neuronal circuit crucial for the processing of short-term memory is affected by pain. The circuit, established between the prefrontal cortex and the hippocampus, is essential for encoding and retaining temporary memories on spatial information. The researchers used multi-electrodes implanted in the brain to record neuronal activity during a behaviour dependent of spatial memory - the animals were trained in a maze where they had to choose between two alternative paths and then asked to recall their chosen path.

The results show that after a painful injury there is a significant reduction in the amount of information that passes through the circuit. This could mean a loss of ability to process information on spatial localization memory, or that those regions critical to memory are now “overwhelmed” by the painful stimuli disrupting the flow of information for memory.

According to Vasco Gallardo, the team ” has already demonstrated that peripheral nerve injury induces an instability in the spatial coding capacity of hippocampus neurons “, where is seen “a clear reduction in their capacity to encode information on the location of the animal.”

So to the author “this new work contributes to the demonstration that chronic pain induces alterations in the function of brain circuits that are not directly connected to tactile or painful processes”. So as a result of chronic pain it is seen that “are also affected neuronal circuits linked to the processing of memories and emotions, what might mean a need for larger and more integrative strategies in the treatment of painful pathologies”, says the researcher.

Human memory study adds to global debate

An international study involving researchers from the University of Adelaide has made a major contribution to the ongoing scientific debate about how processes in the human brain support memory and recognition.

The study used a rare technique in which data was obtained from within the brain itself, using electrodes placed inside the brains of surgery patients.

Obtained in Germany, the data was sent to the University of Adelaide’s School of Psychology for further analysis using new techniques developed there. The results are published today in the Proceedings of the National Academy of Sciences (PNAS).

"Being able to understand how human memory works is important because there is a range of conditions that affect memory, such as Alzheimer’s disease, head injury, and ageing," says Professor John Dunn, Head of the School of Psychology at the University of Adelaide and a co-author of the study, which was led by researchers at the universities of Cambridge, UK, and Bonn, Germany.

"Scientists know a lot about memory from years of study, but there is an ongoing debate about how certain mechanisms in the brain process memory, and how those mechanisms work together.

"What we’re looking at is how the human brain processes ‘recognition memory’, which is our ability to recognise people, objects or events that we’ve encountered in the past."

The debate has centered on two key regions in the brain:

• the hippocampus, which is very important to memory and is one of the first regions of the brain to suffer damage from Alzheimer’s disease; and
• the perirhinal cortex, which receives sensory information from all of the body’s sensory regions.

"The debate is whether or not these two regions work in the same or different ways to support memory and recognition Studies over the years have led to both conclusions," Professor Dunn says.

He says this new study, which uses data from inside the brain instead of from electrodes on the scalp, far from the critical regions, revealed that different processes are at work in the hippocampus and the perirhinal cortex.

"Our analysis shows that these regions are responding to and processing memory in two very different ways. The activity levels in those regions changed in different ways according to the amount of information that could be remembered," Professor Dunn says.

"This study won’t settle the debate once and for all, but it does add weight to those scientists who believe that these two distinct parts of the brain respond to memory in different ways," he says.