Featured Research

from universities, journals, and other organizations

Long-term memory stored in the cortex

Date:
August 27, 2013
Source:
Max-Planck-Gesellschaft
Summary:
'Where' and 'how' memories are encoded in a nervous system is one of the most challenging questions in biological research. The formation and recall of associative memories is essential for an independent life. The hippocampus has long been considered a centre in the brain for the long-term storage of spatial associations. Now, researchers have provided the first experimental evidence that a specific form of memory associations is encoded in the cerebral cortex and is not localized in the hippocampus as described in most neuroscience textbooks. The new study is a game changer since it strongly suggests that the motor cortical circuits itself, and not the hippocampus, is used as memory storage.

Memories (red) for associating (or linking) two different sensations are formed in the cortex (tone in blue and touch in yellow).
Credit: MPI f. Medical Research/Splettstoesser

'Where' and 'how' memories are encoded in a nervous system is one of the most challenging questions in biological research. The formation and recall of associative memories is essential for an independent life. The hippocampus has long been considered a centre in the brain for the long-term storage of spatial associations. Now, Mazahir T. Hasan at the Max Planck Institute for Medical Research and José Maria Delgado-Garcìa at the University Pablo de Olavide of Seville, Spain, were able to provide first experimental evidence that a specific form of memory associations is encoded in the cerebral cortex and is not localized in the hippocampus as described in most neuroscience textbooks. The new study is a game changer since it strongly suggests that the motor cortical circuits itself, and not the hippocampus, is used as memory storage.

Henry Molaison, known widely as H.M., is a famous name in memory research. Large parts of the American's hippocampus -- the region of the brain that is a major element in learning and memory processes -- were removed in the 1950s in an attempt to cure his epileptic seizures. He subsequently suffered severe memory lapses and was no longer able to remember virtually anything new he had learned. Most scientists thereby concluded that the hippocampus is the site of long-term memory.

However, the extent of H.M.'s brain damage was obviously underestimated, because other regions in addition to the hippocampus were also removed or damaged in the surgical procedure. The researchers from Heidelberg and Seville have therefore investigated the learning behaviour of genetically modified mice in which NMDA receptors are turned off only in the motor cerebral cortex. NMDA receptors bind the neurotransmitter glutamate to the synapses and become active when several signals feed into one synapse at the same time. They are the central molecular elements of learning processes, being involved in increasing or decreasing transmission of the signals to synapses.

As the new study shows, in the motor cortex this so-called synaptic plasticity no longer functions without the NMDA receptors. The scientists were thus able to rule out the hippocampus or other regions as the cause for their observations. Based on the new findings, it is the cerebral cortex, not the hippocampus that is the storage site for some forms of memory.

In behaviour tests, so called eyeblink conditioning, animals with and without NMDA receptors in the primary motor cortex had to learn to link a tone with a subsequent electrical stimulus of the eyelid. This association of two sensory inputs involves the cerebellum which coordinates the necessary movements, as well as the hippocampus and the cerebral cortex, which are important learning and memory centres. "After a learning phase, the animals' reflex is to close their eye when they hear just the tone. Without NMDA receptors in the primary motor cerebral cortex, the genetically modified mice on the other hand cannot remember the connection between the tone and electrical stimulus, and therefore they keep their eyes open despite the tone," explains Mazahir T. Hasan of the Max Planck Institute for Medical Research.

The researchers have thus complemented the findings of their Heidelberg-based colleagues that the hippocampus is not the seat of memory. In July 2012, Rolf Sprengel and Peter Seeburg from the Max Planck Institute for Medical Research discovered that mice without NMDA receptors in the hippocampus are still quite capable of learning. "We now think that the hippocampus provides the necessary environmental cues, which are transmitted to the cortex where learning-dependent associations take place. Memories are thus stored at various sites in the cerebral cortex on a long-term basis," explains Hasan.

The findings of Hasan and Delgado-Garcìa thus represent a paradigm-shift in memory research as they make clear that the cerebral cortex is the brain region where memory associations are linked and stored -- not the hippocampus. An advanced and detailed knowledge of the mechanisms for the acquisition, consolidation, and recall of associations in the brain is the prerequisite for a therapeutic treatment of the devastating effects of memory loss in various neurological diseases, such as amnesia, Alzheimer`s disease and dementia.


Story Source:

The above story is based on materials provided by Max-Planck-Gesellschaft. Note: Materials may be edited for content and length.


Journal Reference:

  1. Mazahir T. Hasan, Samuel Hernández-González, Godwin Dogbevia, Mario Treviño, Ilaria Bertocchi, Agnès Gruart, José M. Delgado-García. Role of motor cortex NMDA receptors in learning-dependent synaptic plasticity of behaving mice. Nature Communications, 2013; 4 DOI: 10.1038/ncomms3258

Cite This Page:

Max-Planck-Gesellschaft. "Long-term memory stored in the cortex." ScienceDaily. ScienceDaily, 27 August 2013. <www.sciencedaily.com/releases/2013/08/130827091629.htm>.
Max-Planck-Gesellschaft. (2013, August 27). Long-term memory stored in the cortex. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2013/08/130827091629.htm
Max-Planck-Gesellschaft. "Long-term memory stored in the cortex." ScienceDaily. www.sciencedaily.com/releases/2013/08/130827091629.htm (accessed July 25, 2014).

Share This




More Mind & Brain News

Friday, July 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Beatings and Addiction: Pakistan Drug 'clinic' Tortures Patients

Beatings and Addiction: Pakistan Drug 'clinic' Tortures Patients

AFP (July 24, 2014) — A so-called drugs rehab 'clinic' is closed down in Pakistan after police find scores of ‘patients’ chained up alleging serial abuse. Duration 03:05 Video provided by AFP
Powered by NewsLook.com
New Painkiller Designed To Discourage Abuse: Will It Work?

New Painkiller Designed To Discourage Abuse: Will It Work?

Newsy (July 24, 2014) — The FDA approved Targiniq ER on Wednesday, a painkiller designed to keep users from abusing it. Like any new medication, however, it has doubters. Video provided by Newsy
Powered by NewsLook.com
Can Watching TV Make You Feel Like A Failure?

Can Watching TV Make You Feel Like A Failure?

Newsy (July 24, 2014) — A study by German researchers claims watching TV while you're stressed out can make you feel guilty and like a failure. Video provided by Newsy
Powered by NewsLook.com
China's Ageing Millions Look Forward to Bleak Future

China's Ageing Millions Look Forward to Bleak Future

AFP (July 24, 2014) — China's elderly population is expanding so quickly that children struggle to look after them, pushing them to do something unexpected in Chinese society- move their parents into a nursing home. Duration: 02:07 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

    Health News

      Environment News

        Technology News



          Save/Print:
          Share:  

          Free Subscriptions


          Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

          Get Social & Mobile


          Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

          Have Feedback?


          Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
          Mobile iPhone Android Web
          Follow Facebook Twitter Google+
          Subscribe RSS Feeds Email Newsletters
          Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins