For the final SciBar of the year, Peter Wigmore joins to talk about "The Hippocampus - A Memorable Part of the Brain"
The temporal lobe is part of the side of the brain and the hippocampus is located within the temporal lobe. The word "hippocampus" actually means "sea horse". Obviously. It is quite a small part of the brain and until around 50 years ago, people thought that it didn't really have much of a function.
We don't know what causes temporal lobe epilepsy but there is an electrical storm within the temporal lobe, which then spreads through the brain, causing fitting. One famous patient, known as HM, developed temporal lobe epilepsy in the 1950s. There really wasn't much treatment back then and so they decided to try cutting away part of the temporal lobe and so an 8cm strip was removed from the patient's brain. The epilepsy was cured but something strange happened to his memory. He could remember his childhood, so his long-term memory seemed intact and he could remember things from a couple of minutes ago. However, he couldn’t remember yesterday - he could no longer convert short-term memories into long-term ones.
There are two main parts to the hippocampus - the CA region and the dentate gyrus and the structure of the hippocampus is unique. These parts forma a tri-synaptic circuit, which is unusual for the brain as it is a one-way circuit - it has a direct input and a direct output. It's also an adaptive circuit that changes with activity.
Alzheimer's disease is related to two structural changes in the brain - tangles and plaques, the build-up of both starts in the temporal lobe, which is why Alzheimer's effects the memory.
In London, research was carried out on the brains of taxi drivers and bus drivers, comparing the sizes of the respective hippocampi. It showed that taxi drivers had a bigger hippocampus - taxi drivers are continually having to come up with new routes while bus drivers follow the same route day in, day out. However, the research did only show correlation - there was no evidence of causation but the longer that drivers had been driving taxis, the bigger the hippocampus they had.
Can the brain grow new nerve cells? There are parts of the brain that continue to grow throughout adult life and a strip of stem cells grows on the inside of the dentate gyrus at the rate of around 20,000 neurons every day. There are a number of things that can decrease the rate of growth of these neurons - irradiation/anti-mitotic drugs; aging; stress; depression; smoking cannabis and alcohol. However, it's not all bad news as there are several factors that can increase the rate - exercise; enriched environment; stroke; growth factors; antidepressants; epilepsy and tetrahydrocannabinol. A couple of those might sound a little strange but a stroke results in a regenerative response and the electricity associated with epilepsy simulates growth.
The hippocampus is also responsible for pattern separation - this includes both spotting subtle changes and pattern completion. Recent research has looked at creating a semantic map of the brain - the meaning of words and which parts of the brain the recognition of those words occurs in. The hippocampus isn't really used to "store" words but it is used in language as part of the pattern work that it does.
SciBar returns to The Vat & Fiddle on the 31st of January at 7:30pm
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