Critical review of “Differential Effects of Normal Aging on Memory For Odor –Place and Object-Place Associations” and “Inhibitory Control of Memory in Normal Ageing: Dissociation Between Impaired Intentional and Preserved Unintentional Processes”
As medical advances and healthy lifestyle choices allow people to live to longer, age-related changes in memory are of particular interest to researchers. In their article “Differential Effects of Normal Aging on Memory for Odor-Place and Object-Place Associations,” Gilbert et. al. (2008) describes an experimental study that used associative memory tasks to assess the ability of young and aged individuals to remember odor-place and object-place associations. In this study, the independent variable was age and the dependent variable was performance on the associative memory tasks (# of errors). The authors selected young participants from a student research pool at San Diego State University and aged participants from a group of healthy older individuals already involved in a longitudinal study at San Diego State University. Older study participants were screened for dementia using the Dementia Rating Scale and the Mini-Mental State Examination, two cognitive tasks that are well described in the literature. Also, all study participants were tested for impairment in odor, object and special location recognition and any data from individuals showing these impairments was not included in the study.
Memory for odor-place and object-place associations was tested in two distinct tasks. To assess memory for odor-place associations, participants were presented with a black board clearly marked with 12 white circles indicating 12 spatial locations. During an initial study phase, participants were presented with an odor in a jar for 5 seconds and then the odor jar was placed in a random spatial location on the blackboard for 5 seconds. Participants were told to remember the spatial location of the odor jar. Thirty seconds later, a second odor was presented in the same fashion. In total, each participant was presented with 6 odors that were placed at 6 distinct spatial locations on the board. During a testing phase, each participant was presented with each of the odors (presented in random order) and asked to identify the location on the black board associated with the odor. The number of correct and incorrect associations was recorded. Object-place associations were tested in the same way except that participants were presented with objects instead of odors which they were able to visually inspect for 5 seconds before they were placed in distinct spatial locations on the board. Correct and incorrect pair associations were recorded. Interestingly, aged individuals performed worse than young on the odor-place association task, committing significantly more errors. In contrast, aged individuals performed on par with young on the object-place association task exhibiting no significant difference in the number of errors.
Memory decline in aging is also the research topic of a second article entitled “Inhibitory control of memory in normal ageing; Dissociation between impaired intentional and preserved unintentional processes.” In this paper, Collette and colleagues (2009) examine the integrity of intentional and unintentional inhibitory control of memory in young and aged individuals. The ability to forget unimportant information is crucial to maintaining optimal working memory and previous research highlighted by the authors indicate that this ability to forget (by inhibitory control) declines with age. In this experimental study, the authors explore whether inhibitory control is altered in age by conducting set of memory tasks previously established as valid tests for intentional and unintentional inhibitory control. As in the previous study, the independent variable is age and the dependent variables are the performance measures of the memory tests. Participants were young and aged native French speaking individuals who volunteered for this study. Verbal ability was assessed in all individuals to determine if any volunteers exhibited verbal deficits. Aged individuals were screened for dementia using the Mattis Dementia Rating Scale. Participants were tested on tasks that required intentional and unintentional inhibitory memory control. These tasks assessed working, episodic and semantic memory. The authors hypothesized that intentional inhibitory control would be impaired in older study participants. In accordance with their predictions, the findings of this study revealed that aged and young individuals performed equally on tasks that required unintentional inhibitory control. However, older participants performed significantly worse than young in tasks that required intentional inhibitory control. These findings indicate that intentional inhibitory control of memory declines in aging while unintentional inhibitory control of memory is preserved across the lifetime.
Critique of the Research Studies
Both of these studies present findings about age-related differences in memory ability. The fact that these studies identify memory deficits in aged individuals that are essentially healthy, active members of the community makes their findings particularly interesting. All aged individuals were assessed for cognitive decline that could have inaccurately skewed results, making the reader feel that the findings are valid and reliable. In both cases, the authors did interpret their data in the context of previous studies and appear to have done so correctly. All of the experiments in these studies were performed in accordance with institutional review board guidelines and seemed to have employed the appropriate ethical safeguards.
Both of these studies were performed on humans and provide evidence for memory decline as described by the authors. It would be interesting to see some of these questions answered in animal models where the neurobiology underlying these deficits can be more thoroughly explored. This would be particularly applicable to the study by Gilbert et. al. where they report significant age-related changes in the olfactory system and the memory systems associated with odor memory. Also, discerning odors is much more complicated than visually discerning objects and the results they report may be due to this difference in task difficulty. The authors mention this in the paper but I think it may play a greater role in the study outcome than the authors imply. Relating to the second study by Collette et. al, animal models would be very helpful to explore how inhibitory control is altered at the neuronal network level. Extending these studies to animal models may lead to identifying ways to treat age related changes in memory.
Collette and colleagues highlight an important note when they point out that while aged participants performed significantly worse than young in the tasks that required intentional inhibitory control, their performance is still well above the performance of individuals with frontal lobe damage and pathological conditions such as schizophrenia. This observation clearly shows that aged related cognitive decline is distinct from pathological memory decline and provides much support for the continued study of cognitive decline in normal aging.
References
Collette, F., Germain, S., Hogge, M., & Van der Linden, M. (2009). Inhibitory control of memory in normal ageing: dissociation between impaired intentional and preserved unintentional processes. Memory, 17(1), 104-122.
Gilbert, P. E., Pirogovsky, E., Ferdon, S., Brushfield, A. M., & Murphy, C. (2008). Differential effects of normal aging on memory for odor-place and object-place associations. Exp Aging Res, 34(4), 437-452.
