For our last blog post in January 2016, we are indeed lucky Dr Shibley Rahman has once again found time in his incredible schedule as an academic and author to write this research wrap for us.
Thank you Shibley, as without volunteers like yourself, and others, it would be difficult indeed to offer the kinds of services and information we are able to offer to our members, all people with dementia, and which are all provided at no charge to them.
Shibley writes:
In this ‘research roundup’ for Dementia Alliance International, I’d like to describe some of the latest developments in memory research.
I will explain how they relate to some classic historic research.
And also I explain why this is relevant to our current understanding of dementia.
Memory impairment is a prominent defining feature of Alzheimer's disease, yet the degree to which the profile of memory impairment is uniform across patients is not fully resolved. Alzheimer’s disease is the most common form of dementia worldwide.
Recall or retrieval of memory refers to the subsequent re-accessing of events or information from the past, which have been previously encoded and stored in the brain.
Recognition is the association of an event or physical object with one previously experienced or encountered, and involves a process of comparison of information with memory, e.g. recognising a known face, true/false or multiple choice questions, etc.
That there’s a difference has been interesting to cognitive neurologists for ages.
And crucial when it comes to developing new tests in the clinic to develop and distinguish some types of dementia.
Intriguingly, some researchers - Craik and colleagues - recently described a person “VL” (published 2014).
VL was a female who exhibited frequent episodes of erroneous recollections triggered by everyday events.
Based on neuropsychological testing, VL was classified as living with dementia, and indeed was given a diagnosis of probable Alzheimer׳s disease.
Her memory functions were uniformly impaired but her verbal abilities were generally well preserved. A structural MRI brain scan showed extensive areas of gray matter atrophy particularly in frontal and medial-temporal (MTL) areas of the brain.
Results of experimental recognition tests showed that VL had very high false alarm rates on tests using visual pictures, faces and auditory stimuli, but lower false alarm rates on verbal tests.
This is interesting from the point of view that visual and verbal memory might be organised differently in the human brain.
On a different note, it has been unclear to what extent memory is affected in another type of dementia known as frontotemporal lobar degeneration.
Since persons living with this dementia usually have atrophy in regions implicated in memory function, the frontal and/or temporal lobes of the brain, one would expect some memory impairment (see for example and colleagues, 2008).
And this prediction has been generally borne out in clinical observations.
There’s a part of the brain which historically has been associated with aspects of memory - the hippocampus.
This is really classic work.
Scoville and Milner (1957) described the seminal case of H.M. who fell off his bicycle when he was 7 years old, injuring his head. H.M. began to have epileptic seizures when he was 10. By the age of 27 the epileptic attacks prevented him from living a normal life.
Scoville performed an experimental surgery on H.M.’s brain to stop the seizures. Specifically he removed parts of HM's temporal lobes (part of his hippocampus along with it). The seizures stopped but H.M. had amnesia for the rest of his life.
This case study of H.M. provides information on how particular brain areas and networks are involved in memory processing. This helped scientists to formulate new theories about memory functioning.
H.M. could no longer store new memories (anterograde amnesia). Most of his memories from before the operation remained intact (partial retrograde amnesia).
It’s from work like this that people have been drawn to believe that the hippocampus play a critical role in converting memories of experiences from short term memory to long term memory (“the permanent store”).
H.M. was able to retain some memories for events that happened long before his surgery. This indicates that the medial temporal region with the hippocampus is not the site of permanent storage in itself. It rather seems to play a role in how memories are organised and then stored elsewhere in the brain.
All of this is fascinating in relation to the very commonly held observation about the decline of memory in people living with Alzheimer’s disease: that memory for new events declines comes before the decline in old memories.
This is introduced, indeed, in the ‘bookcase analogy’ of the “Dementia Friends” information sessions which originated in England.
Bringing this all right up to date, Patai and colleagues have recently investigated further the role of the hippocampus part of the brain (2015).
The availability of a large cohort of patients who had sustained relatively selective hippocampal damage early in life enabled us to determine which type of mnemonic deficit showed a correlation with extent of hippocampal injury.
They assessed their patient cohort on a test that provides measures of recognition and recall that are equated for difficulty and found that the patients' performance on the recall tests correlated significantly with their hippocampal volumes.
However, they also found that their performance on the equally difficult recognition tests did not and, indeed, was largely unaffected regardless of extent of hippocampal loss of volume.
The results provide new evidence in favour of the view that the hippocampus is essential for recall but not for recognition.
So, the story continues. This excellent research benefits our understanding of dementia, and how we can develop new ways of identifying and people living with memory problems “living beyond dementia” (Swaffer, 2015).
References
Craik FI, Barense MD, Rathbone CJ, Grusec JE, Stuss DT, Gao F, Scott CJ5 Black SE. VL: a further case of erroneous recollection. Neuropsychologia. 2014 Apr;56:367-80. doi: 10.1016/j.neuropsychologia.2014.02.007. Epub 2014 Feb 20.
Patai EZ, Gadian DG, Cooper JM, Dzieciol AM, Mishkin M, Vargha-Khadem F. Extent of hippocampal atrophy predicts degree of deficit in recall. Proc Natl Acad Sci U S A. 2015 Oct 13;112(41):12830-3. doi: 10.1073/pnas.1511904112. Epub 2015 Sep 28.
Scoville WB, Milner, B. Loss of recent memory after bilateral hippocampal lesions. J Neurol Neurosurg Psychiatry. 1957 Feb;20(1):11-21.
Söderlund H, Black SE, Miller BL, Freedman M, Levine B. Episodic memory and regional atrophy in frontotemporal lobar degeneration. Neuropsychologia. 2008 Jan 15;46(1):127-36. Epub 2007 Aug 9.
Swaffer, K. Living beyond dementia website https://livingbeyonddementia.wordpress.com (accessed 27 January 2016).