Although we are not always aware of it, we are all constantly creating and retrieving visual memories. We need to encode new faces and places and recognize old ones, essentially requiring the brain to change all the time. Impairments in the brain’s ability to change gravely affect our life and are often caused by head trauma and degenerative diseases, such as Alzheimer’s. But what lies in the basis of this crucial function?
A synapse is a junction between neurons that relays information; the electrical changes in the pre synaptic cell affect the post synaptic cell. This process is usually mediated through the release of a neurotransmitter (a chemical agent transmitting neuronal signals) by the pre synaptic neuron.
“Synaptic plasticity” is a term describing the ability of a synapse to change its properties and become weaker or stronger depending on various factors. Long term depression (LTD), which was the focus of the research at hand, is one of the forms of synaptic plasticity. The LTD process is a gradual long term weakening of a synapse caused by a number of subsequent low frequency stimuli received by the post synaptic neuron. It is largely believed that synaptic plasticity is very important to the creation and alternation of memories but it is still not quite clear what the nature of this link is.
It is widely accepted that the perirhinal cortex plays a key role in visual recognition memory and the researchers’ hypothesis was that disrupting synaptic plasticity, and specifically LTD in the perirhinal cortex, would influence memory. Bashir and his colleagues identified the molecular mechanism that controls LTD in the perirhinal cortex and found a peptide capable of inhibiting the process.
They injected the test group rats with that peptide and the control group rats were injected with a peptide which has no effect on LTD. The rats were then put through a memory recognition test. The test group performed badly on the task of recognizing familiar objects, while the control group performed normally. Other memory functions, such as spatial memory, remained unharmed in both groups. These results suggest that a process critical for the expression of LTD in perirhinal cortex underlies visual recognition memory.
According to the researchers, they now plan to research the processes that enable memories to be kept in the brain for long periods of time, and will try to understand why they are damaged with age.
TFOT has previously covered a research conducted at the WeizmannInstitute, in which scientists discovered an enzyme capable of erasing memories by disrupting the synapse maintenance. TFOT has also published stories on Alzheimer’s disease research. One of these stories acquainted you with the discovery of a possible physical source of the Alzheimer’s disease identified by a group from UCLA, and another is an account of a collaborative research project conducted by neuroscientists from several universities, in which a protein complex causing cognitive decline and loss of memory was discovered.
More information about Prof Bashir’s research can be found here.