A new study has revealed that neural inhibition and balanced neural activity in a specific area of the brain is required for recognition memory. The findings could help provide better understanding of cognitive disorders, including schizophrenia, dementia, and age-related memory impairments.
Scientists from the University of Nottingham's School of Psychology, in collaboration with colleagues from the University of Manchester, found that neural inhibition within the hippocampus, but not the prefrontal cortex, is important for object recognition memory. More specifically, both too little and too much neural inhibition in the hippocampus disrupted such memory, suggesting that balanced levels of neural activity in the hippocampus are important for object recognition to function optimally. The findings have been published today in The Journal of Neuroscience.
Neurons in the brain interact with each other by releasing chemicals, so-called neurotransmitters. Gamma-aminobutyric acid (GABA) is the most common inhibitory neurotransmitter, which is important to restrain neural activity, preventing neurons from getting too trigger-happy and from firing too much or responding to irrelevant stimuli.
In the extreme, impaired inhibitory GABA transmission can cause epileptic seizures. In addition, more subtle impairments in GABA-mediated neural inhibition, especially in the hippocampus and prefrontal cortex, two brain regions implicated in memory and other cognitive functions, have been linked to a range of brain disorders characterised by cognitive impairments, including schizophrenia, age-related cognitive decline and early stages of Alzheimer's.
Charlie Taylor, now a Research Fellow in the School of Medicine, led the research as part of her PhD project in the School of Psychology. She said: "Impaired GABAergic neural inhibition in the prefrontal cortex and hippocampus has emerged as a key neuropathological feature of cognitive disorders, but we did not know if these brain abnormalities contribute to memory impairment relevant to these conditions. Many cognitive disorders show impairments in recognition memory, which is a type of memory that allows people to remember newly encountered objects (e.g. their new bike, a new gadget, a new face, etc.). We can test a type of memory related to this in rats using an object recognition test, which is widely used in preclinical models of brain disorders. Using a rat model, we were able to change GABA-mediated neural inhibition specifically in the hippocampus or prefrontal cortex and identify exactly how this affected their recognition of objects."
The researchers found that both too little and too much neural inhibition in the hippocampus disrupts recognition memory, suggesting that balanced levels of neural inhibition are needed to maintain this type of memory function. The findings also show that the object recognition test, which is widely used by researchers in academia and drug discovery industry, can be used to study dysfunction of GABA-mediated neural inhibition in the hippocampus (but not prefrontal cortex) in rat models of brain disorders and also to test new treatments targeting such dysfunction.
These findings provide further understanding of brain mechanisms underlying cognitive impairments, including problems with memory. People often assume that cognitive impairments are caused by decreased activity in certain brain regions, and that 'boosting' brain activity may improve brain functions. However, these new findings show that that the opposite can be the case! Faulty neural inhibition, which leads to increased, but poorly controlled, brain activity can cause problems. This has important implications for new treatments, suggesting that it is important to re-balance neural activity, for example by drugs or neuromodulation technology, in specific brain regions to restore cognitive functions, such as memory.
