Biomedical subjects

Neal J Cohen

Publications and source records attributed to Neal J Cohen.

14 recordsLinked to original sources

PubMed2006

The long and the short of it: relational memory impairments in amnesia, even at short lags.

Classic studies of amnesia led to characterizations of hippocampal function emphasizing involvement in long-term memory rather than short-term (or working) memory. In two experiments, we show that when memory for relations among co-occurring items is tested, hippocampal amnesia results in a deficit even at very short lags. Hence, we find evidence for hippocampal involvement in relational memory, even at short lags normally considered the province of working memory.

Amnesia↗

PubMed2006

Event-related potential signatures of relational memory.

Various lines of evidence suggest that memory for the relations among arbitrarily paired items acquired prior to testing can influence early processing of a probe stimulus. The event-related potential experiment reported here was designed to explore how early in time memory for a previously established face-scene relationship begins to influence processing of faces, under sequential presentation conditions in which a preview of the scene can promote expectancies about the to-be-presented face. Prior to the current work, the earliest component documented to be sensitive to memory for the relations among arbitrarily paired items was the late positive complex (LPC), but here relational memory effects were evident as early as 270-350 msec after face onset. The latency of these relational memory effects suggests that they may be the precursor to similar effects observed in eye movement behavior. As expected, LPC amplitude was also affected by memory for face-scene relationships, and N400 amplitude reflected some combination of memory for items and memory for the relations among items.

Adolescent↗

PubMed2005

Development of shared information in communication despite hippocampal amnesia.

This study investigated the ability of individuals with amnesia to acquire referential labels across a series of collaborative, dynamic interactions with a communication partner. Despite their inability to learn arbitrary relations in paired-associate learning, the amnesic patients showed remarkably robust collaborative learning across trials, at a rate equal to that of normal comparison subjects. The amnesic participants' learning resulted in their arriving at labels for a set of abstract shapes (tangrams), thus facilitating rapid and efficient communication. The labels generated and used by the amnesics during interactions with their partners became simpler across trials, with most labels stabilizing long before the end of training and then being used consistently throughout; moreover, they endured long after the task had ended. These findings have important implications for understanding the memory systems involved in semantic learning and in acquiring shared knowledge ('common ground') among communication partners, and the nature of hippocampal-dependent versus hippocampal-independent learning.

Adult↗

PubMed2005

Selective sparing of brain tissue in postmenopausal women receiving hormone replacement therapy.

Determining the benefits and/or drawbacks of hormone replacement therapy (HRT) on women's health is an imperative public health goal. Research in rodents suggests benefits of estrogen on neuronal growth and function. However, little research has investigated the effects of HRT on brain tissue in humans. We used high-resolution magnetic resonance imaging and an optimized voxel-based morphometric technique to examine the effects of HRT on brain volume in postmenopausal women. We report two main results: (a) HRT is associated with the sparing of grey matter in prefrontal, parietal, and temporal brain regions and white matter in medial temporal lobe regions, and (b) longer durations of therapy are associated with greater sparing of grey matter tissue. HRT should be considered a possible mediator of age-related neural decline in both grey and white matter tissues.

Age Factors↗

PubMed2005

Imaging implicit perception: promise and pitfalls.

The study of implicit perception - perception in the absence of awareness - has a long history. Decades of behavioural work have identified crucial theoretical and methodological issues that must be considered when evaluating claims of implicit perception. Neuroimaging methods provide an important new avenue for illuminating our understanding of perception both with and without awareness, but most imaging experiments have not met the rigorous conditions that the behavioural work has shown are necessary for inferring implicit perception. Here, we review the literature of both behavioural and neuroimaging studies, and note the pitfalls of studying implicit perception as well as the promise that neuroimaging studies have for providing insights about implicit perception when combined with appropriately rigorous behavioural measures of awareness.

Animals↗

PubMed2004

Cardiovascular fitness, cortical plasticity, and aging.

Cardiovascular fitness is thought to offset declines in cognitive performance, but little is known about the cortical mechanisms that underlie these changes in humans. Research using animal models shows that aerobic training increases cortical capillary supplies, the number of synaptic connections, and the development of new neurons. The end result is a brain that is more efficient, plastic, and adaptive, which translates into better performance in aging animals. Here, in two separate experiments, we demonstrate for the first time to our knowledge, in humans that increases in cardiovascular fitness results in increased functioning of key aspects of the attentional network of the brain during a cognitively challenging task. Specifically, highly fit (Study 1) or aerobically trained (Study 2) persons show greater task-related activity in regions of the prefrontal and parietal cortices that are involved in spatial selection and inhibitory functioning, when compared with low-fit (Study 1) or nonaerobic control (Study 2) participants. Additionally, in both studies there exist groupwise differences in activation of the anterior cingulate cortex, which is thought to monitor for conflict in the attentional system, and signal the need for adaptation in the attentional network. These data suggest that increased cardiovascular fitness can affect improvements in the plasticity of the aging human brain, and may serve to reduce both biological and cognitive senescence in humans.

Aged↗

PubMed2004

Behavioral conflict, anterior cingulate cortex, and experiment duration: implications of diverging data.

We investigated the relationship between behavioral measures of conflict and the degree of activity in the anterior cingulate cortex (ACC). We reanalyzed an existing data set that employed the Stroop task using functional magnetic resonance imaging [Milham et al., Brain Cogn 2002;49:277-296]. Although we found no changes in the behavioral measures of conflict from the first to the second half of task performance, we found a reliable reduction in the activity of the anterior cingulate cortex. This result suggests the lack of a strong relationship between behavioral measurements of conflict and anterior cingulate activity. A concomitant increase in dorsolateral prefrontal cortex activity was also found, which may reflect a tradeoff in the neural substrates involved in supporting conflict resolution, detection, or monitoring processes. A second analysis of the data revealed that the duration of an experiment can dramatically affect interpretations of the results, including the roles in which particular regions are thought to play in cognition. These results are discussed in relation to current conceptions of ACC's role in attentional control. In addition, we discuss the implication of our results with current conceptions of conflict and of its instantiation in the brain. Hum. Brain Mapping 21:96-105, 2004.

Adult↗

PubMed2004

Processing and short-term retention of relational information in amnesia.

In a recent eye-movement study [Psychol. Sci. 11 (2000) 454], amnesic patients failed selectively to exhibit long-term effects of memory for the relations among the constituent elements of scenes. This failure could be due to a deficit specifically in long-term relational memory, as we have suggested; or in retention of relational information over any delay, whether involving perceptual processing and short-term maintenance or long-term memory, consistent with suggestions from recent studies of the hippocampus; or in on-line processing of relational information, as would occur in perceptual or feature binding. Here we show robust eye-movement effects of relations among elements of scenes in amnesia in a short-delay matching task, with the same materials and in the same amnesic patients in which long-delay conditions elicited failure. These findings document intact processing and short-term retention of relational information in amnesia, indicating that amnesia associated with hippocampal damage results in a relational memory deficit, specifically of long-term memory.

Amnesia↗

PubMed2004

The nature of change detection and online representations of scenes.

This article provides evidence for implicit change detection and for the contribution of multiple memory sources to online representations. Multiple eye-movement measures distinguished original from changed scenes, even when college students had no conscious awareness for the change. Patients with amnesia showed a systematic deficit on 1 class of eye-movement measures of change detection, even though conscious awareness was not required for the effect to be observed. The authors' findings suggest that online representations of scenes are (a) built up across viewings, (b) composed of activated information from both long-term and working memory, and (c) directly compared with currently processed information regarding the external world. Subsequent online processing is influenced by these representations even when the results of the comparison are not accessible for verbal report.

Adolescent↗

PubMed2003

Aerobic fitness reduces brain tissue loss in aging humans.

BACKGROUND: The human brain gradually loses tissue from the third decade of life onward, with concomitant declines in cognitive performance. Given the projected rapid growth in aged populations, and the staggering costs associated with geriatric care, identifying mechanisms that may reduce or reverse cerebral deterioration is rapidly emerging as an important public health goal. Previous research has demonstrated that aerobic fitness training improves cognitive function in older adults and can improve brain health in aging laboratory animals, suggesting that aerobic fitness may provide a mechanism to improve cerebral health in aging humans. We examined the relationship between aerobic fitness and in vivo brain tissue density in an older adult population, using voxel-based morphometric techniques. METHODS: We acquired high-resolution magnetic resonance imaging scans from 55 older adults. These images were segmented into gray and white matter maps, registered into stereotaxic space, and examined for systematic variation in tissue density as a function of age, aerobic fitness, and a number of other health markers. RESULTS: Consistent with previous studies of aging and brain volume, we found robust declines in tissue densities as a function of age in the frontal, parietal, and temporal cortices. More importantly, we found that losses in these areas were substantially reduced as a function of cardiovascular fitness, even when we statistically controlled for other moderator variables. CONCLUSIONS: These findings extend the scope of beneficial effects of aerobic exercise beyond cardiovascular health, and they suggest a strong solid biological basis for the benefits of exercise on the brain health of older adults.

Aged↗

PubMed2003

Evaluating the neuropsychological dissociation evidence for multiple memory systems.

This article presents a critical evaluation of the logic and nature of the neuropsychological dissociation evidence that has provided one of the essential lines of support for claims of multiple memory systems--specifically, suggesting that amnesia selectively compromises, and an intact hippocampal system selectively supports, a particular form of memory. An analysis of the existing neuropsychological dissociation evidence is offered in which different classes of evidence--different dissociation approaches-are identified and characterized. The logic of these neuropsychological dissociation approaches is evaluated critically in terms of their ability to distinguish among alternative theoretical views. We conclude that although they support a multiple memory systems account, the findings from these types of neuropsychological dissociation, taken individually and without support from other converging lines of cognitive neuroscience evidence, cannot definitively rule out alternative formulations. A more powerful neuropsychological dissociation approach is then outlined, involving dissociation within condition, that, by more effectively limiting the critical domains of difference between the dissociated performances, can successfully rule out alternative accounts. Its application in Ryan, Althoff, Whitlow, and Cohen (2000) is described, providing strong support for the power of the dissociation within condition approach.

Cognitive Science↗

PubMed2002

Attentional control in the aging brain: insights from an fMRI study of the stroop task.

Several recent studies of aging and cognition have attributed decreases in the efficiency of working memory processes to possible declines in attentional control, the mechanism(s) by which the brain attempts to limit its processing to that of task-relevant information. Here we used fMRI measures of neural activity during performance of the color-word Stroop task to compare the neural substrates of attentional control in younger (ages: 21-27 years old) and older participants (ages: 60-75 years old) during conditions of both increased competition (incongruent and congruent neutral) and increased conflict (incongruent and congruent neutral). We found evidence of age-related decreases in the responsiveness of structures thought to support attentional control (e.g., dorsolateral prefrontal and parietal cortices), suggesting possible impairments in the implementation of attentional control in older participants. Consistent with this notion, older participants exhibited more extensive activation of ventral visual processing regions (i.e., temporal cortex) and anterior inferior prefrontal cortices, reflecting a decreased ability to inhibit the processing of task-irrelevant information. Also, the anterior cingulate cortex, a region involved in evaluatory processes at the level of response (e.g., detecting potential for error), showed age-related increases in its sensitivity to the presence of competing color information. These findings are discussed in terms of newly emerging models of attentional control in the human brain.

Aged↗

PubMed2002

Theoretical and computational analysis of skill learning, repetition priming, and procedural memory.

This article analyzes the relationship between skill learning and repetition priming, 2 implicit memory phenomena. A number of reports have suggested that skill learning and repetition priming can be dissociated from each other and are therefore based on different mechanisms. The authors present a theoretical analysis showing that previous results cannot be regarded as evidence of a processing dissociation between skill learning and repetition priming. The authors also present a single-mechanism computational model that simulates a specific experimental task and exhibits both skill learning and repetition priming, as well as a number of apparent dissociations between these measures. These theoretical and computational analyses provide complementary evidence that skill learning and repetition priming are aspects of a single underlying mechanism that has the characteristics of procedural memory.

Cognition↗

PubMedDate not supplied

Effects of aerobic fitness training on human cortical function: a proposal.

We briefly review the extant human and animal literature on the influence of fitness training on brain, cognition and performance. The animal research provides clear support for neurochemical and structural changes in brain with fitness training. The human literature suggests reliable but process specific changes in cognition with fitness training for young and old adults. We describe a research program which examines the influence of aerobic fitness training on the functional activity of the human using event-related functional magnetic resonance imaging, of humans in fitness interventions.

Adult↗