Summary: A new study reports memory and attention impairments may be a result of increased activity in the hippocampus.
Source: University of Nottingham.
Neurons in the brain interact by sending each other chemical messages, 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.
Researchers led by Dr Tobias Bast in the School of Psychology at The University of Nottingham have found that faulty inhibitory neurotransmission and abnormally increased activity in the hippocampus impairs our memory and attention.
Their latest research — “Hippocampal neural disinhibition causes attentional and memory deficits” — published in the academic journal Cerebral Cortex, has implications for understanding cognitive deficits in a variety of brain disorders, including schizophrenia, age-related cognitive decline and Alzheimer’s, and for the treatment of cognitive deficits.
The hippocampus — a part of the brain that sits within our temporal lobes — plays a major role in our everyday memory of events and of where and when they happen — for example remembering where we parked our car before going shopping.
This research has shown that a lack of restraint in the neural firing within the hippocampus disrupts hippocampus-dependent memory; in addition, such aberrant neuron firing within the hippocampus also disrupted attention — a cognitive function that does not normally require the hippocampus.
Increased activity can be more detrimental than reduced activity
Dr Bast, said: “Our research carried out in rats highlights the importance of GABAergic inhibition within the hippocampus for memory performance and for attention. The finding that faulty inhibition disrupts memory suggests that memory depends on well-balanced neural activity within the hippocampus, with both too much and too little causing impairments. This is an important finding because traditionally, memory impairments have mainly been associated with reduced activity or lesions of the hippocampus.
“Our second important finding is that faulty inhibition leading to increased neural activity within the hippocampus disrupts attention, a cognitive function that does not normally require the hippocampus, but depends on the prefrontal cortex. This probably reflects that there are very strong neuronal connections between hippocampus and prefrontal cortex. Our finding suggests that aberrant hippocampal activity has a knock-on effect on the prefrontal cortex, thereby disrupting attention.”
“Overall, our new findings show that increased activity of a brain region, due to faulty inhibitory neurotransmission, can be more detrimental to cognitive function than reduced activity or a lesion. Increased activity within a brain region can disrupt not only the function of the region itself — in this case hippocampus-dependent memory — but also the function of other regions to which it is connected — in this case prefrontal cortex-dependent attention.”
Adding to existing research findings
Dr Bast’s research is motivated by recent clinical findings that patients in early stages of schizophrenia, age-related cognitive decline and Alzheimer’s show faulty inhibition and increased activity within the hippocampus. The new study, where inhibition in the hippocampus of rats was disrupted before the animals took part in tests of attention and memory, revealed that such faulty inhibition and aberrant activity within the hippocampus causes the type of memory and attentional impairments seen in patients.
This research adds to the team’s recent findings, where they found that attention was disrupted by faulty inhibition and increased activity within the prefrontal cortex, a brain region important for attention.
Dr Bast, said: “Overall, these findings highlight that higher brain functions, such as attention and memory, depend on well-balanced neural activity within the underlying brain regions.”
Potential target for new treatments
This research has important implications for treating cognitive impairments.
The findings show that simply ‘boosting’ the activity of the key memory and attention centres in the brain (the hippocampus and prefrontal cortex), which has been a long-standing strategy for cognitive enhancement, will not necessarily improve memory and attention, but can actually impair these functions. What’s important is to re-balance activity within these regions.
Dr Bast, said: “One emerging idea is that early stages of cognitive disorders, such as schizophrenia and age-related cognitive decline and Alzheimer’s, are characterised by faulty inhibition and too much activity; this excess neural activity leads then to neuronal damage and the reduced brain activity characterizing later stages of these disorders. So, rebalancing aberrant activity early on may not only restore attention and memory, but also prevent further decline.
“We have new studies on the way where we aim to identify medicines that might be able to re-balance neural activity within hippocampus and prefrontal cortex and to restore memory and attention.”
About this neuroscience research article
Source: Lindsay Brooke – University of Nottingham Image Source: NeuroscienceNews.com image is in the public domain. Original Research:Abstract for “Hippocampal Neural Disinhibition Causes Attentional and Memory Deficits” by Stephanie McGarrity, Rob Mason, Kevin C. Fone, Marie Pezze and Tobias Bast in Cerebral Cortex. Published online July 18 2016 doi:10.1093/cercor/bhw247
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]University of Nottingham. “Increased Hippocampal Activity Impairs Memory and Attention.” NeuroscienceNews. NeuroscienceNews, 23 August 2016. <https://neurosciencenews.com/hippocampus-activity-memory-attention-4896/>.[/cbtab][cbtab title=”APA”]University of Nottingham. (2016, August 23). Increased Hippocampal Activity Impairs Memory and Attention. NeuroscienceNew. Retrieved August 23, 2016 from https://neurosciencenews.com/hippocampus-activity-memory-attention-4896/[/cbtab][cbtab title=”Chicago”]University of Nottingham. “Increased Hippocampal Activity Impairs Memory and Attention.” https://neurosciencenews.com/hippocampus-activity-memory-attention-4896/ (accessed August 23, 2016).[/cbtab][/cbtabs]
Hippocampal Neural Disinhibition Causes Attentional and Memory Deficits
Subconvulsive hippocampal neural disinhibition, that is reduced GABAergic inhibition, has been implicated in neuropsychiatric disorders characterized by attentional and memory deficits, including schizophrenia and age-related cognitive decline. Considering that neural disinhibition may disrupt both intra-hippocampal processing and processing in hippocampal projection sites, we hypothesized that hippocampal disinhibition disrupts hippocampus-dependent memory performance and, based on strong hippocampo-prefrontal connectivity, also prefrontal-dependent attention. In support of this hypothesis, we report that acute hippocampal disinhibition by microinfusion of the GABA-A receptor antagonist picrotoxin in rats impaired hippocampus-dependent everyday-type rapid place learning performance on the watermaze delayed-matching-to-place test and prefrontal-dependent attentional performance on the 5-choice-serial-reaction-time test, which does not normally require the hippocampus. For comparison, we also examined psychosis-related sensorimotor effects, using startle/prepulse inhibition (PPI) and locomotor testing. Hippocampal picrotoxin moderately increased locomotion and slightly reduced startle reactivity, without affecting PPI. In vivo electrophysiological recordings in the vicinity of the infusion site showed that picrotoxin mainly enhanced burst firing of hippocampal neurons. In conclusion, hippocampal neural disinhibition disrupts hippocampus-dependent memory performance and also manifests through deficits in not normally hippocampus-dependent attentional performance. These behavioral deficits may reflect a disrupted control of burst firing, which may disrupt hippocampal processing and cause aberrant drive to hippocampal projection sites.
“Hippocampal Neural Disinhibition Causes Attentional and Memory Deficits” by Stephanie McGarrity, Rob Mason, Kevin C. Fone, Marie Pezze and Tobias Bast in Cerebral Cortex. Published online July 18 2016 doi:10.1093/cercor/bhw247