Welcome to the Dickerson Lab: Memory
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Human memory abilities are critical to everyday life, and encompass a wide range of specific cognitive functions. These abilities tend to be divided into declarative and non-declarative types of memory. Declarative (or explicit) memory usually means the kinds of memory that a person is aware of and can consciously use to make decisions. It is often tested using verbal abilities (e.g., "tell me all the words I just read to you," or "tell me as much as you remember of the story that I just told you."). Declarative memory is often subdivided into episodic memory, semantic memory, and working memory. Non-declarative memory usually refers to so-called procedural memory (or skill learning), such as riding a bike or playing an instrument and people may have limited capacity to describe these kinds of memories in words. Since these different kinds of memory are subserved by different brain systems, people can have problems with one form of memory and not other forms. This can lead to some of the surprising aspects of preserved abilities in some patients with prominent impairment in a given domain of memory (e.g., why some patients can still play a complex piano piece from memory but 5 minutes later can't remember having done it).
Episodic memory
Since 1995, we have studied aspects of episodic memory in cognitively intact individuals and in individuals with brain disorders, including Alzheimer's disease and related disorders, stroke and cerebrovascular disease, and epilepsy. These studies have focused in particular on standard laboratory tests of the acquisition and retrieval of new information, with a particular focus on free recall (coming up with information on your own) and recognition memory (multiple-choice type tests of whether or not words or pictures have been encountered before). There are a series of special topics that we have been pursuing along the way, some of which we are just beginning to explore systematically:
Semantic memory
Since 2006 we have pursued investigations of semantic memory. These studies have been motivated in part by the loss of semantic memory (i.e., encyclopedic knowledge of facts) that can be seen in patients with various neurologic disorders, including semantic dementia, primary progressive aphasia, certain kinds of strokes and brain injuries or infections, and to a greater or lesser degree in Alzheimer's disease. The interactions between semantic memory and episodic memory have also been of particular interest--how is it that people use their knowledge of what things are to organize (or "chunk") new information as it comes in?
Working memory
Since 2005, we have been performing studies of working memory, or immediate "on-line" storage and manipulation of information in order to perform a task or achieve a goal. Some of these studies have been performed in patients with Alzheimer's disease, posterior cortical atrophy (PCA), primary progressive aphasia, frontotemporal dementia, and related disorders, as well as patients with multiple sclerosis. We believe it is possible to see relatively preserved episodic memory even when working memory is strikingly impaired, but it can be difficult to demonstrate this observation using tests. Therefore, we are in the process of developing new tests to try to better understand these issues.
Publications related to memory
- Miller SL, Celone K, DePeau K, Diamond E, Dickerson BC, Rentz D, Pihlajamaki M, Sperling RA. Age-related memory impairment associated with loss of parietal deactivation but preserved hippocampal activation. PNAS 2008 Feb 12;105(6):2181-2186.
- Dickerson BC, Miller SL, Greve DN, Dale AM, Albert MS, Schacter DL, Sperling RA. Prefrontal-hippocampal-fusiform activity during encoding predicts intra-individual differences in free recall ability: An event-related functional-anatomic MRI study. Hippocampus 2007 Jun 29; [Epub ahead of print].
- Celone KA, Calhoun VD, Dickerson BC, Atri A, Chua EF, Miller SL, DePeau K, Rentz DM, Selkoe DJ, Blacker D, Albert MS, Sperling RA. Alterations in memory networks in mild cognitive impairment and Alzheimer's disease: an independent component analysis. J Neuroscience 2006; 26(40):10222-10231.
- Dickerson BC, Salat DH, Greve DN, Chua EF, Rand-Giovanetti E, Rentz DM, Bertram L, Mullin K, Tanzi RE, Blacker D, Albert MS, Sperling RA. Increased hippocampal activation in mild cognitive impairment compared to normal aging and AD. Neurology 2005 65:404-411.
- Dickerson BC, Salat D, Bates J, Atiya M, Killiany R, Greve D, Dale A, Stern CE, Blacker D,
Albert MS, Sperling RA. Medial temporal lobe function and structure in mild cognitive
impairment. Annals of Neurology 2004;56:27-35.
- When people are asked to look at pictures they have never seen before and try to learn them for future memory testing, the hippocampus and other parts of the medial temporal lobe memory system "activate" to a greater degree than when they are asked to look at familiar pictures. This activity can be measured by functional MRI scanning while people are lying down in the scanner (looking pictures through a mirror that are being projected down the MRI tube). In the present study, this procedure was done with individuals with mild cognitive impairment. Despite similar performance on the easy memory task, the individuals with relatively greater memory impairment in daily life demonstrated relatively greater hippocampal activity while learning the new pictures. The individuals with relatively greater hippocampal atrophy recruited a greater proportion of the remaining hippocampus to successfully do the task. They were also the ones who declined in daily life over the coming 2 years. This was the first demonstration of hippocampal/MTL hyperactivation in MCI, which has since been seen by other researchers. We interpreted it as occurring due to possible compensation for the disease process (presumably AD) taking place in the memory system.
- deToledo-Morrell L, Dickerson BC, Sullivan MP, Spanovic C, Wilson R, Bennett DA. Hemispheric
differences in hippocampal volume predict verbal and spatial memory performance in patients with
Alzheimer's disease. Hippocampus 2000; 10:136-42.
- Although AD is usually thought to affect the brain in a fairly symmetric fashion, there can be asymmetries within any given group of patients. We took advantage of this situation to investigate the relationship between the level of hippocampal atrophy on the right vs. the left in relation to verbal vs. spatial memory. We hypothesized, based on work in patients with epilepsy, that in a group of patients with AD relatively greater right hippocampal atrophy would be associated with relatively greater impairment in memory for spatial locations of visual objects (line drawings on cards, 4 per card), whereas relatively greater left hippocampal atrophy would be associated with relatively greater impairment in memory for the names of those objects. The results supported this hypothesis, suggesting a reason for some of the differences that can be seen between patients who all have AD but may have relatively more shrinkage of one brain region than the other. Generally, this study also shows what can be learned from investigating brain-behavior relationships within a single group of individuals with a particular disease.