Biomedical subjects

Cheryl L Grady

Publications and source records attributed to Cheryl L Grady.

At least 19 recordsLinked to original sources

PubMed2006

Age effects on social cognition: faces tell a different story.

The authors administered social cognition tasks to younger and older adults to investigate age-related differences in social and emotional processing. Although slower, older adults were as accurate as younger adults in identifying the emotional valence (i.e., positive, negative, or neutral) of facial expressions. However, the age difference in reaction time was largest for negative faces. Older adults were significantly less accurate at identifying specific facial expressions of fear and sadness. No age differences specific to social function were found on tasks of self-reference, identifying emotional words, or theory of mind. Performance on the social tasks in older adults was independent of performance on general cognitive tasks (e.g., working memory) but was related to personality traits and emotional awareness. Older adults also showed more intercorrelations among the social tasks than did the younger adults. These findings suggest that age differences in social cognition are limited to the processing of facial emotion. Nevertheless, with age there appears to be increasing reliance on a common resource to perform social tasks, but one that is not shared with other cognitive domains.

Adult↗

PubMed2006

Age-related changes in brain activity across the adult lifespan.

A number of theories have emerged to explain the well-studied changes in memory that occur with age. Many of these theories invoke mechanisms that have the potential to affect multiple cognitive domains, in addition to memory. Such mechanisms include alterations in attentional or inhibitory function, or dysfunction of specific brain areas, such as the frontal lobes. To gain insight into these mechanisms, we used functional magnetic resonance imaging to examine brain activity during encoding and recognition tasks in young, middle-aged, and older adults to identify correlations between age and brain activity across the various tasks. The goal was to see whether these correlations were task-specific or common across tasks, and to determine whether age differences emerged in a linear fashion over the adult years. Across all memory tasks, at both encoding and recognition, linear increases of activity with age were found in areas normally decreased during task performance (e.g., medial frontal and parietal regions), whereas activity in regions with task-related activation (e.g., dorsolateral prefrontal cortex) decreased with age. These results suggest that there is a gradual, age-related reduction in the ability to suspend non-task-related or "default-mode" activity and engage areas for carrying out memory tasks. Such an alteration in the balance between default-mode and task-related activity could account for increased vulnerability to distraction from irrelevant information, and thereby affect multiple cognitive domains.

Adult↗

PubMed2005

Task-related activity in prefrontal cortex and its relation to recognition memory performance in young and old adults.

Older adults often have more widespread prefrontal cortex (PFC) activation during memory retrieval tasks, compared to young adults, particularly in the left hemisphere. Recruitment of additional frontal activity in older adults has been attributed by some researchers to compensation, perhaps for reduced activity elsewhere in the brain, whereas others have described it as a non-selective response that may be due to a failure to inhibit these PFC regions. To address further the impact of PFC activity on memory in older adults, we used PET to measure brain activity during recognition memory tasks. Both young and old adults showed increased activity during recognition, compared to a control task, in bilateral PFC. Young adults showed greater activation of left hippocampus and lateral temporal cortex during recognition, whereas older adults showed greater activity in the right inferior frontal gyrus. Age differences also were seen in correlations between brain activity and memory performance. There were positive correlations between activity in the right parahippocampal gyrus and recognition performance in young adults, whereas positive correlations between activity in PFC and performance were found only in older adults. These positive correlations included the right inferior PFC region where older adults had greater activation. Activity in this right PFC region was negatively correlated with medial temporal activity in both groups. These results provide further evidence for age-specific patterns of brain activity underlying memory performance and are consistent with the idea that PFC assumes a larger role in supporting successful recognition memory with increasing age. The negative correlation between activity in PFC and medial temporal regions, as well as the age differences in how these regions were related to behavior, suggest that those older individuals who recruit PFC to a greater degree may do so as a compensatory response to reductions in medial temporal regions.

Adult↗

PubMed2005

The relation between brain activity during memory tasks and years of education in young and older adults.

Higher education is associated with less age-related decline in cognitive function, but the mechanism of this protective effect is unknown. The authors examined the effect of age on the relation between education and brain activity by correlating years of education with activity measured using functional MRI during memory tasks in young and older adults. In young adults, education was negatively correlated with frontal activity, whereas in older adults, education was positively correlated with frontal activity. Medial temporal activity was associated with more education in young adults but less education in older adults. This suggests that the frontal cortex is engaged by older adults, particularly by the highly educated, as an alternative network that may be engaged to aid cognitive function.

Adult↗

PubMed2005

Neuroimaging the serial position curve. A test of single-store versus dual-store models.

Neuroimaging data could help clarify the long-standing dispute between dual-store and single-store models of the serial position curve. Dual-store models assume that retrieval from late positions is dependent on short-term memory (STM), whereas retrieval from early positions is dependent on long-term memory (LTM). Single-store models, however, assume that retrieval processes for early and late items are similar, but that early items are more difficult to discriminate than late items. The present study used functional magnetic resonance imaging to examine this question. Ten young adults were scanned while they recognized items from early or late serial positions. Recognition of early items uniquely activated brain areas traditionally associated with LTM, namely, regions within the hippocampal memory system. None of these areas was activated for retrieval of late items. These results indicate differential use of LTM retrieval processes, and therefore support dual-store models over single-store models.

Adult↗

PubMed2005

The functional organization of auditory working memory as revealed by fMRI.

Spatial and nonspatial auditory tasks preferentially recruit dorsal and ventral brain areas, respectively. However, the extent to which these auditory differences reflect specific aspects of mental processing has not been directly studied. In the present functional magnetic resonance imaging experiment, participants encoded and maintained either the location or the identity of a sound for a delay period of several seconds and then subsequently compared that information with a second sound. Relative to sound localization, sound identification was associated with greater hemodynamic activity in the left rostral superior temporal gyrus. In contrast, localizing sounds recruited greater activity in the parietal cortex, posterior temporal lobe, and superior frontal sulcus. The identification differences were most prominent during the early stage of the trial, whereas the location differences were most evident during the late (i.e., comparison) stage. Accordingly, our results suggest that auditory spatial and identity dissociations as revealed by functional imaging may be dependent to some degree on the type of processing being carried out. In addition, dorsolateral prefrontal and lateral superior parietal areas showed greater activity during the comparison as opposed to the earlier stage of the trial, regardless of the type of auditory task, consistent with results from visual working memory studies.

Adult↗

PubMed2004

Remembering our past: functional neuroanatomy of recollection of recent and very remote personal events.

Functional magnetic resonance imaging was used to study brain regions implicated in retrieval of memories that are decades old. To probe autobiographical memory, family photographs were selected by confederates without the participant's involvement, thereby eliminating many of the variables that potentially confounded previous neuroimaging studies. We found that context-rich memories were associated with activity in lingual and precuneus gyri independently of their age. By contrast, retrosplenial cortex was more active for recent events regardless of memory vividness. Hippocampal activation was related to the richness of re-experiencing (vividness) rather than the age of the memory per se. Remote memories were associated with distributed activation along the rostrocaudal axis of the hippocampus whereas activation associated with recent memories was clustered in the anterior portion. This may explain why circumscribed lesions to the hippocampus disproportionately affect recent memories. These findings are incompatible with theories of long-term memory consolidation, and are more easily accommodated by multiple-trace theory, which posits that detailed memories are always dependent on the hippocampus.

Adult↗

PubMed2004

"I have often walked down this street before": fMRI studies on the hippocampus and other structures during mental navigation of an old environment.

The role of the hippocampus in recent spatial memory has been well documented in patients with damage to this structure, but there is now evidence that the hippocampus may not be needed for the storage and recovery of a spatial layout that was experienced long before injury. Such preservation may rely, instead, on a network of dissociable, extra-hippocampal regions implicated in topographical orientation. Using functional magnetic resonance imaging (fMRI), we investigated this hypothesis in healthy individuals with extensive experience navigating in a large-scale urban environment (downtown Toronto). Participants were scanned as they performed mental navigation tasks that emphasized different types of spatial representations. Tasks included proximity judgments, distance judgments, landmark sequencing, and blocked-route problem-solving. The following regions were engaged to varying degrees depending on the processing demands of each task: retrosplenial cortex, believed to be involved in assigning directional significance to locales within a relatively allocentric framework; medial and posterior parietal cortex, concerned with processing space within egocentric coordinates during imagined movement; and regions of prefrontal cortex, present in tasks heavily dependent on working memory. In a second, event-related experiment, a distinct area of inferotemporal cortex was revealed during identification of familiar landmarks relative to unknown buildings in addition to activation of many of those regions identified in the navigation tasks. This result suggests that familiar landmarks are strongly integrated with the spatial context in which they were experienced. Importantly, right medial temporal lobe activity was observed, its magnitude equivalent across all tasks, though the core of the activated region was in the parahippocampal gyrus, barely touching the hippocampus proper.

Adult↗

PubMed2004

The influence of sex on limbic volume and perfusion in AD.

The goal of the current study was to determine whether Alzheimer's disease (AD) pathology affects the limbic system of men and women differently as measured by in vivo neuroimaging. Magnetic resonance imaging (MRI) and coregistered single photon emission computed tomography (SPECT) were used to examine the limbic system in 20 men and 20 women with probable AD compared to 40 age- and education-matched normal controls (20 men, 20 women). Limbic volumes and relative perfusion values were obtained from the MR images and coregistered SPECT scans, respectively. No significant differences were found between sexes in limbic volumes or relative perfusion values in the normal controls. Many limbic regions were significantly affected in both men and women with AD compared to normal controls. However, only the men with AD displayed atrophy in the orbitofrontal cortex, middle and posterior cingulate cortices, hypothalamus, and mamillary bodies, and relative hypoperfusion in the anterior and middle cingulate cortices. Women with AD exclusively showed anterior thalamic atrophy. Separating men and women did not substantially improve diagnostic classification.

Aged↗

PubMed2004

Assessing the auditory dual-pathway model in humans.

Evidence from anatomical and neurophysiological studies in nonhuman primates suggests a dual-pathway model of auditory processing wherein sound identity and sound location information are segregated along ventral and dorsal streams, respectively. The present meta-analysis reviewed evidence from auditory functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies to determine the reliability of this model in humans. Activation coordinates from 11 "spatial" studies (i.e., listeners made localization judgements on sounds that could occur at two or more perceptually different positions) and 27 "nonspatial" studies (i.e., listeners completed nonspatial tasks involving sounds presented from the same location) were entered into the analysis. All but one of the spatial studies reported activation within the inferior parietal lobule as opposed to only 41% of the nonspatial studies. In addition, 55% of spatial studies reported activity around the superior frontal sulcus as opposed to only 7% of the nonspatial studies. In comparison, inferior frontal activity (Brodmann's areas 45 and 47) was reported in only 9% of the spatial studies, but in 56% of the nonspatial studies. Finally, almost all temporal lobe activity observed during spatial tasks was confined to posterior areas, whereas nonspatial activity was distributed throughout the temporal lobe. These results support an auditory dual-pathway model in humans in which nonspatial sound information (e.g., sound identity) is processed primarily along the ventral stream whereas sound location is processed along the dorsal stream and areas posterior to primary auditory cortex.

Animals↗

PubMed2003

Evidence from functional neuroimaging of a compensatory prefrontal network in Alzheimer's disease.

Previous experiments have found that individuals with Alzheimer's disease (AD) show increased activity in prefrontal regions compared with healthy age-matched controls during cognitive tasks. This has been interpreted as compensatory reallocation of cognitive resources, but direct evidence for a facilitating effect on performance has been lacking. To address this we measured neural activity during semantic and episodic memory tasks in mildly demented AD patients and healthy elderly controls. Controls recruited a left hemisphere network of regions, including prefrontal and temporal cortices in both the semantic and episodic tasks. Patients engaged a unique network involving bilateral dorsolateral prefrontal and posterior cortices. Critically, activity in this network of regions was correlated with better performance on both the semantic and episodic tasks in the patients. This provides the most direct evidence to date that AD patients can use additional neural resources in prefrontal cortex, presumably those mediating executive functions, to compensate for losses attributable to the degenerative process of the disease.

Adaptation, Physiological↗

PubMed2003

Age-related differences in the functional connectivity of the hippocampus during memory encoding.

The purpose of the current experiment was to examine the functional connectivity of the hippocampus during encoding in young and old adults, and the way in which this connectivity was related to recognition performance. Functional connectivity was defined as the correlation between activity in the hippocampus and activity in the rest of the brain, as measured by neuroimaging. During encoding of words and pictures of objects in young adults, hippocampal activity was correlated with activity in the ventral prefrontal and extrastriate regions, and increased activity in all these regions was associated with better recognition. In contrast, older adults showed correlations between hippocampal activity and the dorsolateral prefrontal and parietal regions, and positive correlations between activity in these regions and better memory performance. This ventral/dorsal distinction suggests a shift in the cognitive resources used with age from more perceptually based processes to those involved in executive and organizational functions. The results of this study provide evidence that aging is associated with alterations in hippocampal function, including how it is functionally connected with prefrontal cortex, and that these alterations have an impact on memory performance.

Adult↗

PubMed2003

An fMRI study investigating cognitive modulation of brain regions associated with emotional processing of visual stimuli.

Brain regions modulated by cognitive tasks during emotional processing were investigated using fMRI. Participants performed indirect and direct emotional processing tasks on positive and negative faces and pictures. We used a multivariate technique, partial least squares (PLS) to determine spatially distributed patterns of brain activity associated with different tasks and stimulus conditions, as well as the interaction between the two. The pattern of brain activity accounting for the most task-related covariance represented a task x stimulus interaction and distinguished indirect processing of pictures and direct processing of faces from direct processing of pictures and indirect processing of faces. The latter two conditions were characterised by limbic (e.g. amygdala, insula, thalamus) and temporal lobe activity, in addition to greater activity in the ventral prefrontal cortex. Indirect and direct processing of pictures and faces, respectively, were represented by more dorsal prefrontal and parietal activity. These findings indicate that brain activity during processing of emotional content is critically dependent on both the type of stimulus and processing task. In addition, these results support the idea that the pattern of activity in the emotional network can be influenced in a 'top-down' fashion via cognitive factors such as attentional control, and as such, have important clinical implications for emotional disorders, such as depression and anxiety.

Adult↗

PubMed2002

The effect of encoding strategy on the neural correlates of memory for faces.

Encoding and recognition of unfamiliar faces in young adults were examined using positron emission tomography to determine whether different encoding strategies would lead to encoding/retrieval differences in brain activity. Three types of encoding were compared: a 'deep' task (judging pleasantness/unpleasantness), a 'shallow' task (judging right/left orientation), and an intentional learning task in which subjects were instructed to learn the faces for a subsequent memory test but were not provided with a specific strategy. Memory for all faces was tested with an old/new recognition test. A modest behavioral effect was obtained, with deeply-encoded faces being recognized more accurately than shallowly-encoded or intentionally-learned faces. Regardless of encoding strategy, encoding activated a primarily ventral system including bilateral temporal and fusiform regions and left prefrontal cortices, whereas recognition activated a primarily dorsal set of regions including right prefrontal and parietal areas. Within encoding, the type of strategy produced different brain activity patterns, with deep encoding being characterized by left amygdala and left anterior cingulate activation. There was no effect of encoding strategy on brain activity during the recognition conditions. Posterior fusiform gyrus activation was related to better recognition accuracy in those conditions encouraging perceptual strategies, whereas activity in left frontal and temporal areas correlated with better performance during the 'deep' condition. Results highlight three important aspects of face memory: (1) the effect of encoding strategy was seen only at encoding and not at recognition; (2) left inferior prefrontal cortex was engaged during encoding of faces regardless of strategy; and (3) differential activity in fusiform gyrus was found, suggesting that activity in this area is not only a result of automatic face processing but is modulated by controlled processes.

Adult↗

PubMed2002

Neural correlates of memory for object identity and object location: effects of aging.

The purpose of this study was to investigate the effects of aging on memory for object identity and object location to determine whether aging affects both posterior neocortical areas that are domain-specific and other brain regions, such as pre-frontal cortex, that are involved in encoding and retrieval regardless of the information that is processed (domain-general). We used positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) in younger and older participants while they were engaged in encoding and retrieving information about object identity and object location. Compared to young adults, older adults showed decreased activation in domain-specific regions of inferior parietal and inferior temporal cortex while engaged in processing (encoding and retrieving) information about object location and object identity, respectively. This decreased specificity in the older adults was accompanied by greater domain-general activation in right prefrontal and premotor cortex during perceptual encoding than during retrieval. Conversely, the younger participants showed greater domain-general activation in right extrastriate cortex (Brodmann area (BA) 18) during retrieval. Moreover, we found that medial temporal and frontal lobes were synergistically activated in younger adults but not in older adults. The pattern of decreased specificity of activation in posterior neocortex with greater activation in anterior neocortex suggests that, with age, compensatory domain-general mechanisms in anterior neocortex are recruited to mitigate altered domain-specific processes. Thus, the results of the present study indicate that the relation between the presumed integrity of various structures, such as the hippocampus, prefrontal cortex, and posterior neocortex, and their pattern of activation, is a complex one that is influenced by age, by the perceptual and cognitive demands of the task and their interaction.

Adult↗

PubMed2002

Introduction to the special section on aging, cognition, and neuroimaging.

In response to the recent increase in the number of laboratories engaged in the use of functional and structural neuroimaging to study cognitive aging, this special section has been compiled to serve as an entry into this area for the readers of Psychology and Aging. These articles are representative of the field and cover many of the issues faced by researchers in this area. This introduction presents some background into the techniques that are used and provides an overview of the articles.

Adult↗

PubMed2002

The effects of encoding task on age-related differences in the functional neuroanatomy of face memory.

Age-related differences in brain activity mediating face recognition were examined using positron emission tomography. Participants encoded faces using a pleasant-unpleasant judgment, a right-left orientation task, and intentional learning. Scans also were obtained during recognition. Both young and old groups showed signficant effects of encoding task on recognition accuracy, but older adults showed reduced accuracy overall. Increased brain activity in older adults was similar to that seen in young adults during conditions associated with deeper processing, but was reduced during the shallow encoding and recognition conditions. Left prefrontal activity was less in older adults during encoding, but greater during recognition. Differential correlations of brain activity and behavior were found that suggest older adults use unique neural systems to facilitate face memory.

Adult↗

PubMed2002

Age-related differences in face processing: a meta-analysis of three functional neuroimaging experiments.

Differences between young and old adults in brain activity, measured with positron emission tomography, were examined during three face processing experiments: episodic memory, working memory, and degraded face perception. Each experiment contained an easy face matching condition and a more difficult processing condition. Young adults showed greater activity in bilateral prefrontal cortex during the memory tasks, compared to face matching, but no difference in prefrontal activity between degraded and nondegraded perception. Older adults, on the other hand, had greater prefrontal activity in both memory and degraded perceptual tasks compared to matching. This suggests that increased prefrontal activity is task-specific in young adults, but, in old adults, is a more general response to increased cognitive effort or need for resources. These data are consistent with the dedifferentiation hypothesis of aging, and suggest a possible neural mechanism for this dedifferentiation, such that dependence on prefrontal activity across a greater number of tasks could also increase the amount of covariance across these tasks.

Adult↗