Summary: A new study has identified brain regions crucial for remembering words and how they are affected in people with temporal lobe epilepsy. Researchers found that shrinkage in the prefrontal, temporal, and cingulate cortices, as well as the hippocampus, was linked to difficulty recalling words.
Using high-resolution MRI scans, they examined 84 epilepsy patients and compared their memory test scores to brain size. Those with smaller brain regions performed worse on verbal memory tasks, highlighting the role of these areas in word recall.
Key Facts:
- Memory and epilepsy: Shrinkage in specific brain regions impairs word recall in epilepsy patients.
- MRI insights: High-resolution scans revealed a link between brain structure and verbal memory performance.
- Surgical applications: Findings may help guide epilepsy surgeries to preserve language and memory functions.
Source: UCL
The parts of the brain that are needed to remember words, and how these are affected by a common form of epilepsy, have been identified by a team of neurologists and neurosurgeons at UCL.
The new study, published in Brain Communications, found that shrinkage in the front and side of the brain (prefrontal, temporal and cingulate cortices, and the hippocampus) was linked to difficulty remembering words.
The new discovery highlights how the network that is involved in creating and storing word memories is dispersed throughout the brain.
This is particularly crucial for helping to understand conditions such as epilepsy, in which patients may have difficulty with remembering words. The researchers hope that their findings will help guide neurosurgical treatment for patients with epilepsy by helping surgeons to avoid parts of the brain important for language and memory, that may otherwise be affected, when doing operations.
Corresponding author, Professor John Duncan (UCL Queen Square Institute of Neurology) said: “Being able to remember and recall words is important for day-to-day memory to work well.
“Detailed MRI brain scans are used to find out the causes of epilepsy and can show if any parts of the brain are shrunken. By measuring the parts of the brain that are shrunken and how well a person can remember words, we can work out which parts of the brain are used for making and storing memories.
“In addition, if medication has not stopped seizures occurring, this helps us to guide neurosurgical treatment for a person’s epilepsy, to avoid damaging the parts of the brain that are needed for memory to work well.”
In the first study of its kind, the researchers examined 84 people with temporal lobe epilepsy (epilepsy arising from the temporal lobe at the sides of the head) and hippocampal sclerosis (a condition in which part of the brain is scarred, and memory is affected) and 43 healthy people.
The patients were divided into those with left-sided and right-sided hippocampal sclerosis.
High-resolution MRI scans were used to measure the size and shape of different parts of the brain, including the cerebral cortex (the outer layer of the brain responsible for thinking, memory, attention, perception, awareness, and language) and specific areas within the hippocampus (the part of the brain that helps with learning, memory, and spatial navigation).
All participants underwent standardised tests to assess their verbal memory. These tests were part of the Adult Memory and Information Processing Battery, which measures how well people can remember and recall words.
The researchers then compared the memory test scores to the sizes of different brain areas, to see if smaller brain parts were linked to worse memory.
They found that smaller sizes in certain brain areas, like the prefrontal, temporal and cingulate cortices, and parts of the hippocampus, were linked to worse memory for words in people with epilepsy arising in their temporal lobes.
These findings are also important for understanding how the brain organises and remembers words.
Lead author, Dr Giorgio Fiore (National Hospital for Neurology and Neurosurgery, UCLH) said: “This research is important as it helps us to understand how memory may fail and may help guide the designing of neurosurgical operations for epilepsy that will not make memory worse.”
Funding: This work was funded by the Epilepsy Research UK and supported by the National Institute for Health and Care Research University College London Hospitals Biomedical Research Centre (NIHR UCLH BRC).
About this language and neuroscience research news
Author: Poppy Tombs
Source: UCL
Contact: Poppy Tombs – UCL
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Cortico-hippocampal networks underpin verbal memory encoding in temporal lobe epilepsy” by John Duncan et al. Brain Communications
Abstract
Cortico-hippocampal networks underpin verbal memory encoding in temporal lobe epilepsy
Knowledge of the structural underpinnings of human verbal memory is scarce. Understanding the human verbal memory network at a finer anatomical scale will have important clinical implications for the management of patients with verbal memory impairment.
In this cross-sectional study, we aimed to assess the contributions of cerebral cortex and hippocampal subfields to verbal memory encoding in temporal lobe epilepsy. We included consecutive patients (n = 84) with radiologically and pathologically defined hippocampal sclerosis (HS) (44 left-sided) and unilateral temporal lobe epilepsy, and healthy volunteers (n = 43) who were comparable regarding age and sex.
The morphometric and volumetric measures of cerebral cortex and hippocampal subfields were extracted from high-resolution MRI scans. People included in this study underwent standardized neuropsychological evaluation, including measures of verbal memory assessed through the Adult Memory and Information Processing Battery.
Verbal memory performances were Z-scores corrected by using means and standard deviations published for sample standardization. Associations between verbal learning Z-scores and the grey matter volume of the cerebral cortex and hippocampal subfields were investigated.
Reduction of grey matter volumes in the left and right medial and dorsolateral prefrontal cortex (Pcorr < 0.0001), superior and middle temporal gyri (Pcorr < 0.0001), anterior and posterior cingulate cortex (Pcorr < 0.0001) and of the left ventrolateral prefrontal cortex (Pcorr < 0.0001) and parietal–temporal–occipital junction (Pcorr < 0.0001) were associated with worse verbal learning.
These findings were consistent across both the entire cohort and in a subgroup analysis focused exclusively on HS patients. Within hippocampi, smaller volumes of the left dentate gyrus (P = 0.003), cornu ammonis 4 (P = 0.005) and cornu ammonis 3 (P = 0.03) were associated with worse verbal learning Z-scores.
This study demonstrates that verbal learning in patients with temporal lobe epilepsy is strongly related to the volume of distinct regions of the prefrontal, temporal and cingulate cortices and left dentate gyrus, cornu ammonis 4 and cornu ammonis 3 hippocampal subfields.
It provides the basis to suggest a corticohippocampal network for verbal learning in these patients, improving our understanding of human verbal memory. These biomarkers may inform attractive targets for forthcoming modulating therapies.
Future work may also analyse the impact of sparing part of the left dentate gyrus, cornu ammonis 4 and cornu ammonis 3 as a protective measure against verbal memory impairment after surgery for temporal lobe epilepsy.
