Dramatic changes to well-known places go unnoticed

How well do we know our city? It turns out, much more poorly than we might imagine. We used declarative memory and eye-tracking techniques to examine people's ability to detect modifications to real-world landmarks and scenes in Toronto locales with which they have had extensive experience. Participants were poor at identifying which scenes contained altered landmarks, whether the modification was to the landmarks' relative size, internal features, or relation to surrounding context. To determine whether an indirect measure would prove more sensitive, we tracked eye movements during viewing. Changes in overall visual exploration, but not to specific regions of change, were related to participants' explicit endorsement of scenes as modified. These results support the contention that very familiar landmarks are represented at a global or gist level, but not local or fine-grained, level. These findings offer a unified view of memory for gist across verbal and spatial domains, and across recent and remote memory, with implications for hippocampal-neocortical interactions.

Cancer-related cognitive impairment: an update on state of the art, detection, and management strategies in cancer survivors

BACKGROUND

Advances in diagnostic and therapeutic strategies in oncology have significantly increased the chance of survival of cancer patients, even those with metastatic disease. However, cancer-related cognitive impairment (CRCI) is frequently reported in patients treated for non-central nervous system cancers, particularly during and after chemotherapy.

DESIGN

This review provides an update of the state of the art based on PubMed searches between 2012 and March 2019 on 'cognition', 'cancer', 'antineoplastic agents' or 'chemotherapy'. It includes the most recent clinical, imaging and pre-clinical data and reports management strategies of CRCI.

RESULTS

Evidence obtained primarily from studies on breast cancer patients highlight memory, processing speed, attention and executive functions as the most cognitive domains impaired post-chemotherapy. Recent investigations established that other cancer treatments, such as hormone therapies and targeted therapies, can also induce cognitive deficits. Knowledge regarding predisposing factors, biological markers or brain functions associated with CRCI has improved. Factors such as age and genetic polymorphisms of apolipoprotein E, catechol-O-methyltransferase and BDNF may predispose individuals to a higher risk of cognitive impairment. Poor performance on neuropsychological tests were associated with volume reduction in grey matter, less connectivity and activation after chemotherapy. In animals, hippocampus-based memory and executive functions, mediated by the frontal lobes, were shown to be particularly susceptible to the effects of chemotherapy. It involves altered neurogenesis, mitochondrial dysfunction or brain cytokine response. An important next step is to identify strategies for managing cognitive difficulties, with primary studies to assess cognitive training and physical exercise regimens.

CONCLUSIONS

CRCI is not limited to chemotherapy. A multidisciplinary approach has improved our knowledge of the complex mechanisms involved. Nowadays, studies evaluating cognitive rehabilitation programmes are encouraged to help patients cope with cognitive difficulties and improve quality of life during and after cancer.

Brain interleukin-1 is involved in spatial memory and passive avoidance conditioning

Within the brain, the inflammatory cytokine interleukin-1 (IL-1) mediates illness-associated neural, neuroendocrine, and behavioral responses; however, its role in normal neurobehavioral processes is not clear. To examine the role of IL-1 signaling in memory, we infused Long-Evans rats intracerebroventricularly with IL-1beta (10 ng/rat), IL-1 receptor antagonist (IL-1ra, 100 microg/rat), or saline immediately following a learning task and tested memory functioning 1-8 days later. In the Morris water maze (MWM), IL-1ra caused memory impairment in the hippocampus-dependent, spatial version, whereas IL-1beta had no effect. Neither IL-1beta nor IL-1ra influenced the hippocampus-independent, nonspatial version of the MWM. In the passive avoidance response, which also depends on hippocampal functioning, IL-1ra caused memory impairment, and IL-1beta caused memory improvement. These results suggest that IL-1 signaling within the hippocampus plays a critical role in learning and memory processes.

New views on old memories: re-evaluating the role of the hippocampal complex

Evidence of temporally graded retrograde amnesia (RA) following hippocampal damage has fuelled the long-standing belief that memory undergoes a consolidation process, whereby memories are progressively modified in neocortical regions until they are independent of the hippocampal (HPC) complex. Support for this position derives from both the animal and human RA literature, although the results are not consistent. Specifically, consolidation theory does not account for loss of episodic (detail) information in humans and context-dependent information in animals, which often extend back for much of the life span. We discuss an alternative approach, the Multiple Trace Theory, which suggests that the HPC complex contributes to the retrieval of recent and remote episodic and context-dependent memories. According to this view, such memory traces are represented as spatially distributed interactions between the HPC and neocortex that persist for as long as those memories exist. On the other hand, semantic, or context-free, memories can become independent of the HPC as consolidation theory predicts. In support of this view, we report recent accounts of relatively flat RA gradients in autobiographical and spatial detail loss in patients and animal models with extensive bilateral HPC lesions. By comparison, temporally graded RA was observed in tests of semantic and context-free memory. We also report neuroimaging studies in which hippocampal activity, elicited during recollection of autobiographical memories, did not distinguish recent from remote episodes. Our discussion suggests ways to reconcile discrepancies in the literature and guide predictions of the occurrence of flat versus temporally limited gradients of remote episodic and semantic memory loss following lesions to HPC.

Dietary protein, carbohydrate, and fat enhance memory performance in the healthy elderly

BACKGROUND

Dietary carbohydrates can improve memory. Whether these effects are related to elevations in blood glucose or to energy ingestion is unknown.

OBJECTIVES

Our objectives were to determine 1) the influence of isoenergetic protein-, carbohydrate-, and fat-containing drinks on cognitive performance and 2) whether the time period after ingestion affects cognition.

DESIGN

After fasting overnight, 11 men and 11 women aged 61-79 y consumed either a 300-mL drink containing 774 kJ as pure protein (whey), carbohydrate (glucose), or fat (safflower oil) or a nonenergy placebo on 4 separate mornings. Cognitive tests were administered 15 and 60 min after ingestion of the drinks. Plasma glucose and serum insulin concentrations were measured.

RESULTS

Only the carbohydrate drink increased blood glucose (P < 0.0001). Compared with the placebo, all 3 macronutrients improved delayed paragraph recall (PR) (P < 0.001) and improved or tended to improve immediate PR (P < 0.04) 15 min after ingestion. Beneficial effects on other cognitive tests were confined to one or more of the macronutrients: carbohydrate improved Trail Making Test (Trails) performance at 60 min (P = 0.02) and tended to improve Trails at 15 min (P = 0.04) and PR at 60 min in men, carbohydrate and fat improved or tended to improve performance on Trails at 15 and 60 min in subjects with poor baseline scores (r > -0.41, P < 0.03), fat tended to improve attention at 60 min (P < 0.05), and protein reduced the rate of forgetting on the PR at 15 min (P = 0.002).

CONCLUSIONS

Energy intake from protein, carbohydrate, or fat can enhance memory independently of elevations in blood glucose. Each macronutrient may also exert unique effects on cognition.

Anterograde and retrograde amnesia in rats with large hippocampal lesions

A test of socially acquired food preferences was used to study the effects of large lesions to the hippocampal formation (HPC) on anterograde and retrograde memory in rats. In the anterograde test, rats with HPC lesions normally acquired the food preference but showed a faster rate of forgetting than control groups. When the food preference was acquired preoperatively, HPC groups exhibited a temporally graded retrograde amnesia in which memory was impaired when the preference was acquired within 2 days of surgery but not at longer delays. The results support the traditional theory that the HPC contributes to the consolidation of newly acquired information into a durable memory trace that is represented in other brain areas. Consistent with this view, the results indicate that, once a memory trace is consolidated, the HPC does not participate in its storage or retrieval. The possibility is considered that extrahippocampal areas in the medial temporal lobe are needed to maintain a memory trace throughout its existence.

Learning and memory in S100-beta transgenic mice: an analysis of impaired and preserved function

S100-beta, a calcium-binding astrocytic protein from chromosome 21, has been implicated in CNS function generally and the hippocampus in particular. Elevated levels of S100-beta have been observed reliably in the brains of patients with Alzheimer's Disease and Down Syndrome. Groups of transgenic mice, carrying multiple S100-beta gene copies, and nontransgenic controls were administered a series of behavioral tests (delayed spatial and nonspatial non-matching-to-sample, radial arm maze, socially acquired food preference) that assessed a wide range of cognitive functions. Consistent with the widespread presence of S100-beta throughout the brain, transgenic mice exhibited learning or memory impairment on all tasks. The dementia-like cognitive profile of S100-beta mice represents a promising model for studying comparable cognitive deficits associated with neurodegenerative diseases.

Glucose treatment reduces memory deficits in young adult rats fed high-fat diets

Feeding rats high-fat diets for 3 months produces a widespread cognitive deficit that affects performance on a wide range of learning and memory tasks. The present study tested the hypothesis that this effect is related to a fat-induced impairment in glucose metabolism. Following 3 months of dietary intervention (20% by weight fat diets, composed primarily of either beef tallow or soybean oil versus standard laboratory chow), male Long-Evans rats were tested on a variable interval delayed alternation (VIDA) task that measures learning and memory functions that differentially involve specific brain regions. Relative to rats fed chow, rats consuming the high-fat diets were impaired on all aspects of VIDA performance. Following baseline testing, rats were maintained on their respective diets and the effect of glucose administration (100 mg/kg BW; i.p.) was examined. For the next 6 days, animals alternately received injections of saline or glucose 30 min prior to VIDA testing. Glucose treatment improved performance, with the effect being most pronounced at the longer intertrial intervals where task performance is sensitive to hippocampal impairment. Importantly, the beneficial effect of glucose were confined to those animals consuming the high-fat diets and were not observed in rats fed chow. These results demonstrate that glucose administration can overcome those deficits associated with hippocampal function in rats fed high-fat diets and are consistent with the hypothesis that high-fat diets, in part, mediate their effect through the development of insulin resistance and glucose intolerance.

Cross-cultural differences in memory: the role of culture-based stereotypes about aging

The extent to which cultural stereotypes about aging contribute to age differences in memory performance is investigated by comparing younger and older Anglophone Canadians to demographically matched Chinese Canadians, who tend to hold more positive views of aging. Four memory tests were administered. In contrast to B. Levy and E. Langer's (1994) findings, younger adults in both cultural groups outperformed their older comparison group on all memory tests. For 2 tests, which made use of visual stimuli resembling ideographic characters in written Chinese, the older Chinese Canadians approached, but did not reach, the performance achieved by their younger counterparts, as well as outperformed the older Anglophone Canadians. However, on the other two tests, which assess memory for complex figures and abstract designs, no differences were observed between the older Chinese and Anglophone Canadians. Path analysis results suggest that this pattern of findings is not easily attributed to a wholly culturally based account of age differences in memory performance.

Episodic encoding and recognition of pictures and words: role of the human medial temporal lobes

In the present PET study, we examined brain activity related to processing of pictures and printed words in episodic memory. Our goal was to determine how the perceptual format of objects (verbal versus pictorial) is reflected in the neural organization of episodic memory for common objects. We investigated this issue in relation to encoding and recognition with a particular focus on medial temporal-lobe (MTL) structures. At encoding, participants saw pictures of objects or their written names and were asked to make semantic judgments. At recognition, participants made yes-no recognition judgments in four different conditions. In two conditions, target items were pictures of objects; these objects had originally been encoded either in picture or in word format. In two other conditions, target items were words; they also denoted objects originally encoded either as pictures or as words. Our data show that right MTL structures are differentially involved in picture processing during encoding and recognition. A posterior MTL region showed higher activation in response to the presentation of pictures than of words across all conditions. During encoding, this region may be involved in setting up a representation of the perceptual information that comprises the picture. At recognition, it may play a role in guiding retrieval processes based on the perceptual input, i.e. the retrieval cue. Another more anterior right MTL region was found to be differentially involved in recognition of objects that had been encoded as pictures, irrespective of whether the retrieval cue provided was pictorial or verbal in nature; this region may be involved in accessing stored pictorial representations. Our results suggest that left MTL structures contribute to picture processing only during encoding. Some regions in the left MTL showed an involvement in semantic encoding that was picture specific; others showed a task-specific involvement across pictures and words. Together, our results provide evidence that the involvement of some but not all MTL regions in episodic encoding and recognition is format specific.

Cross-cultural differences in memory: the role of culture-based stereotypes about aging

The extent to which cultural stereotypes about aging contribute to age differences in memory performance is investigated by comparing younger and older Anglophone Canadians to demographically matched Chinese Canadians, who tend to hold more positive views of aging. Four memory tests were administered. In contrast to B. Levy and E. Langer's (1994) findings, younger adults in both cultural groups outperformed their older comparison group on all memory tests. For 2 tests, which made use of visual stimuli resembling ideographic characters in written Chinese, the older Chinese Canadians approached, but did not reach, the performance achieved by their younger counterparts, as well as outperformed the older Anglophone Canadians. However, on the other two tests, which assess memory for complex figures and abstract designs, no differences were observed between the older Chinese and Anglophone Canadians. Path analysis results suggest that this pattern of findings is not easily attributed to a wholly culturally based account of age differences in memory performance.

Cognitive performance is associated with glucose regulation in healthy elderly persons and can be enhanced with glucose and dietary carbohydrates

BACKGROUND

A glucose drink has been shown to improve memory in persons with poor glucose regulation and poor cognition.

OBJECTIVE

The objective of this study was to determine 1) whether an association between cognition and glucose regulation is apparent in healthy seniors and 2) the effects of dietary carbohydrates on cognition.

DESIGN

After an overnight fast, 10 men and 10 women (aged 60-82 y) consumed 50 g carbohydrate as glucose, potatoes, or barley or a placebo on 4 separate mornings. Cognitive tests were administered 15, 60, and 105 min after ingestion of the carbohydrate. Plasma glucose and serum insulin were measured.

RESULTS

In a multiple regression analysis, poor baseline (placebo) verbal declarative memory (immediate and 20-min delayed paragraph recall and word list recall) and visuomotor task performance were predicted by poor beta cell function, high incremental area under the glucose curve, low insulin resistance, and low body mass index. The difference in plasma glucose after food consumption [glucose > potatoes > barley > placebo (P: < 0.03)] did not predict performance. Although overall performance did not differ with consumption of the different test foods, baseline score and beta cell function correlated with improvements in immediate and delayed paragraph recall for all 3 carbohydrates (compared with placebo); the poorer the baseline memory or beta cell function, the greater the improvement (correlation between beta cell function and improvement in delayed paragraph recall: r > -0.50, P: < 0.03). Poor beta cell function correlated with improvement for all carbohydrates in visuomotor task performance but not on an attention task.

CONCLUSIONS

Glucose regulation was associated with cognitive performance in elderly subjects with normal glucose tolerance. Dietary carbohydrates (potatoes and barley) enhanced cognition in subjects with poor memories or beta cell function independently of plasma glucose.

Event-related potentials during conscious and automatic memory retrieval

The effects of study-test lags of between 0 and 32 items on conscious (C) and automatic (A) memory processes in a running word-completion task were investigated with event-related potentials (ERPs). The process dissociation procedure (PDP) can distinguish between C and A contributions to memory by comparing performance when subjects respond with either an old item (inclusion) or a new item (exclusion). C can be estimated by subtracting the probability of an intrusion of an old item during the exclusion task (due to A without C) from the probability of correctly producing an old item during the inclusion task (due to C and/or A). The behavioral results showed that C was stronger when the test item followed the studied word in the next trial or after a lag of one stimulus. The strength of A did not vary with lag. The ERP waveforms contained a broad parietal positive wave between 300 and 800 ms. This parietal wave distinguished between correctly recalled old and new words. The early portion of this old-new effect was significantly affected by lag. Subtracting waveforms to obtain a measure of C revealed an effect in the later portion of this wave, lateralized over the left hemisphere. A sustained frontal negativity occurred during all recordings and was larger during conscious retrieval. There was no consistent ERP effect related to automatic memory retrieval.

Anterograde and retrograde amnesia after lesions to frontal cortex in rats

A socially acquired food-preference test was used to assess effects of lesions to the frontal cortex on anterograde and retrograde memory in rats. In Experiment 1, there was no effect of lesion when rats were administered a two-choice test in which the target food was to be selected in the presence of a single distractor. In Experiment 2, a three-choice memory test was administered in which the target food was presented along with two equally palatable alternatives. In the latter test, lesioned groups displayed anterograde amnesia that increased with the length of the interval between postoperative acquisition and test, and a severe retrograde amnesia that extended equally over the entire range of intervals between preoperative acquisition and test. This outcome, which contrasted with the pattern of memory loss previously observed in rats with hippocampal lesions on this test, was interpreted as evidence for the strategic role of the frontal lobes in directing response selection and retrieval processes in memory.

Aging and time-of-day effects on cognition in rats

This study used an animal model to investigate the importance of the time at which testing occurs for age differences in learning and memory. Groups of old and young rats were entrained to a 12-hr light-dark schedule and administered tests of delayed alternation and inhibitory avoidance conditioning at the beginning or end of their high-activity cycle. Apart from normal age differences in test performance, the behavioral results demonstrated that old but not young rats were affected by the time of testing. In both tasks, old rats tested late in the activity cycle performed significantly worse than did old rats tested early in the cycle, under conditions that challenged memory processes that are known to involve the hippocampus. The results indicate that circadian disruption in old age can adversely affect memory and related cognitive function, with important implications for inhibitory control.

Source memory and divided attention: reciprocal costs to primary and secondary tasks

Source memory, in comparison with item memory, is more sensitive to frontal lesions and may require more strategic processing. Divided attention was used to restrict attentional resources and strategic processing on memory tasks. Participants encoded and retrieved items (i.e., words) and source (i.e., voice or spatial location) while concurrently performing a finger-tapping (FT) or visual reaction-time (VRT) task. Memory accuracy costs under divided attention were greater for retrieval of source than item and were greater with VRT than FT. Similarly, costs to the secondary task were greater when concurrently retrieving source as opposed to item and were greater for VRT than FT. Effects were stronger when spatial location was used as the source task. Findings support the idea that processing source information requires more attentional resources and effort than processing item information. Furthermore, concurrent performance of VRT produced greater interference with a task that was more dependent on intact frontal functioning and better simulated the performance of patients with frontal dysfunction.

The effects of high fat diets and environmental influences on cognitive performance in rats

As part of a continuing investigation of the relationship between dietary factors and cognitive function, the present study examined the combined effects of environmental influences and high-fat diets on learning and memory. Following 3 months of dietary (20% by weight fat diets, composed primarily of either beef tallow or soybean oil versus standard laboratory chow) and environmental treatments (standard, enriched or impoverished), subjects were tested on a variable interval delayed alternation (VIDA) task which measures learning and memory functions that differentially involve specific brain regions. The results confirmed the negative effects of high fat diets, relative to chow, on all aspects of VIDA performance and showed that environmental enrichment overcame deficits associated with dietary fat. Housing rats fed high-fat diets in an impoverished environment did not further exacerbate cognitive deficits observed in such rats living under standard conditions. By comparison, chow-fed rats exhibited no benefit associated with the enriched environment on any aspect of task performance, and only a transitory learning impairment when housed in an impoverished environment. The results show that high fat diets and environmental conditions influence cognitive function and that these two factors interact with one another to produce different profiles of benefits and impairments.

Environmental influences on cognitive decline in aged rats

Two experiments are reported in which young and old rats, housed in an impoverished (IE), enriched (EE), or standard (SE), environment, were tested on a series of complex, blind-alley mazes. In Experiment 1, 3-months exposure to IE exacerbated age differences in maze performance, relative to the differences between young and old rats in EE and SE. Old rats in the EE and SE conditions did not differ from each other. In Experiment 2, rats were raised for an additional 3 months in either IE or EE before further maze testing. The main findings were that the maze performance of old rats, transferred from IE to EE, improved significantly, whereas the performance of old rats, transferred from SE or EE to IE, declined. These results indicated that the deleterious effects of an impoverished environment on learning and memory are, at least partly, reversible, and that experience in a stimulating environment can protect old rats from the adverse effects of relocation to a deprived environment. Taken together, the results highlight the impact of environmental influences on cognitive function in old age, and emphasize the need to consider nonbiological factors in understanding the process of cognitive aging.

The contribution of impaired working memory monitoring to performance of the self-ordered pointing task in normal aging and Parkinson's disease

The factors contributing to the working memory deficit observed in older adults and individuals with Parkinson's disease on the Self-Ordered Pointing Task were examined in 2 experiments. A detailed analysis of the error data revealed that errors tended to be clustered toward the end of a trial and that this effect was somewhat independent of set size. This pattern was proposed to result from a monitoring deficit where individuals failed to maintain an integrated representation of how far they had proceeded in the trial, an interpretation consistent with animal work by M. Petrides (1995).

Functional interactions between the medial temporal lobes and posterior neocortex related to episodic memory retrieval

We applied structural equation modeling to positron emission tomography data in humans to examine functional interactions between the right medial temporal lobe (MTL) and selected right neocortical regions in relation to visual recognition memory. Using a priori knowledge about anatomical connections between these regions as a guiding constraint, we modeled the pattern of interactions [i.e. covariances in regional cerebral blood flow (rCBF)] associated with episodic memory retrieval of spatial location and compared it with the pattern for retrieval of object identity. We also compared these patterns with those associated with perceptual matching of spatial location and object identity. Although displaying no difference in average rCBF across tasks, the right MTL showed domain-specific qualitative differences in interactions with posterior dorsal (parieto-occipital sulcus, supramarginal gyrus) and ventral regions (fusiform gyrus, superior temporal sulcus) but not with a prefrontal region. MTL interactions involving dorsal regions were positive in the spatial retrieval task but negative for object retrieval. Interactions involving ventral regions showed the reverse pattern. No comparable changes were observed during perceptual matching. Using control models, we demonstrated the neuroanatomical specificity of these results. Our results provide support for the notion that the nature of interactions between the MTL and posterior neocortex depends on the domain of information to-be-recovered.

Clustering and switching on verbal fluency: the effects of focal frontal- and temporal-lobe lesions

We examined the hypothesis that, on verbal fluency, clustering (i.e. generating words within subcategories) is related to temporal-lobe functioning, whereas switching (i.e. shifting between subcategories) is related to frontal-lobe functioning. Tests of phonemic and semantic fluency were administered to 53 patients with focal frontal-lobe lesions (FL), 23 patients with unilateral temporal-lobe lesions (TL) and 55 matched controls. Performance by FL patients was consistent with our hypothesis: in comparison to controls, patients with left-dorsolateral or superior-medial frontal lesions switched less frequently and produced normal cluster sizes on both phonemic and semantic fluency. Performance by TL patients was not consistent across fluency tasks and provided partial support for our hypothesis. On phonemic fluency, TL patients were unimpaired on both switching and clustering. On semantic fluency, TL patients were impaired on switching in comparison to controls and left TL patients produced smaller clusters than right TL patients. The best indices for discriminating the patient groups, therefore, were phonemic-fluency switching (impaired only with frontal lesions) and semantic-fluency clustering (impaired only with temporal-lobe lesions).

Prefrontal cortex and caudate nucleus in conditional associative learning: dissociated effects of selective brain lesions in rats

Rats with lesions to prefrontal cortex (PFC) or caudate nucleus (CN) were compared on tests of conditional associative learning (CAL) that placed varying demands on conditional rule learning and working-with-memory operations that are essential for response selection. Damage to either structure impaired performance, but the respective deficits resulted from disruption of different processes. CN lesions produced a consistent learning deficit that was thought to reflect a basic impairment in forming stimulus-response (S-R) associations. The behavior of PFC rats was more variable and depended on task requirements. When S-R learning or response selection was relatively easy, the PFC was not critical. However, when either component was made more difficult, thus requiring the contribution of strategic processes, PFC damage produced profound impairments. In addition to clarifying the roles of the PFC and CN in CAL, the results provide further evidence that multiple brain regions participate in relatively simple behavioral tasks and that their respective contributions can be dissociated.

Glucose treatment attenuates spatial learning and memory deficits of aged rats on tests of hippocampal function

Groups of old and young rats were administered three tests of spatial learning and memory that are known to be sensitive to hippocampal dysfunction: the radial arm maze (RAM), spatial non-matching-to-sample (SNMTS), and a spatial vs. local cue-preference task. Old rats performed worse than young rats on the RAM and SNMTS tasks; on the cue-preference task, young rats were biased to use spatial cues, whereas old rats exhibited strong preferences for distinct, local cues. Peripheral injections of glucose (100 mg/kg) improved performance by old rats on the RAM and SNMTS, which correlated with measures of glucose metabolism. Glucose treatment did not affect old rats performance on the cue-preference task. There was evidence that glucose-treatment improved performance of young rats in the RAM test, but not the other tests. The results extend the range of tasks on which glucose-induced cognitive enhancement has been demonstrated in aged rats, and provides further evidence that memory loss resulting from hippocampal dysfunction is especially amenable to glucose treatment.

Clustering and switching on verbal fluency tests in Alzheimer's and Parkinson's disease

Two components of verbal fluency performance--clustering (i.e., generating words within subcategories) and switching (i.e., shifting between subcategories)--were examined in patients with dementia of the Alzheimer type (DAT), patients with dementia with Parkinson's disease (DPD), nondemented patients with Parkinson's disease (NPD), and demographically matched controls. The DAT and DPD groups were impaired in the number of words generated on both phonemic and semantic fluency. The DAT group produced smaller clusters on both tasks and switched less often on semantic fluency than controls. The DPD group switched less often on both tasks and produced smaller clusters on phonemic fluency than controls. The NPD group was not impaired on any fluency variable. Thus, the total number of words generated on phonemic and semantic fluency did not discriminate the dementia groups from their respective control groups, but measures of clustering and switching did. This differential pattern of performance provides evidence for the potential usefulness of measures of switching and clustering in the assessment of dementia.

Networks of domain-specific and general regions involved in episodic memory for spatial location and object identity

Positron emission tomography (PET) was used to investigate human episodic memory for spatial location and object identity. We measured regional cerebral bloodflow (rCBF) while subjects engaged in perceptual matching of the location or the identity of line drawings of objects. Perceptual matching also involved incidental encoding of the presented information. Subsequently, rCBF was measured when subjects retrieved the location or the identity of these objects from memory. Using the multivariate partial least squares image analysis, we identified three patterns of activity across the brain that allowed us to distinguish structures that are differentially involved in processing spatial location and object identity from structures that are differentially involved in encoding and retrieval but operate across both domains. Domain-specificity was evident by increased rCBF during the processing of spatial location in the right middle occipital gyrus, supramarginal gyrus, and superior temporal sulcus, and by increased rCBF during the processing of object identity in portions of bilateral lingual and fusiform gyri. There was a nearly complete overlap between domain-specific dorsal and ventral extrastriate cortex activations during perceptual matching and memory retrieval. Evidence of domain-specificity was also found in the prefrontal cortex and the left hippocampus, but the effect interacted with encoding and retrieval. Domain-general structures included bilateral superior temporal cortex regions, which were preferentially activated during encoding, and portions of bilateral middle and inferior frontal gyri, which were preferentially activated during retrieval. Together, our data suggest that encoding and retrieval in episodic memory depend on the interplay between domain-specific structures, most of which are involved in memory as well as perception, and domain-general structures, some of which operate more at encoding and others more at retrieval.

Prefrontal cortex and caudate nucleus in conditional associative learning: dissociated effects of selective brain lesions in rats

Rats with lesions to prefrontal cortex (PFC) or caudate nucleus (CN) were compared on tests of conditional associative learning (CAL) that placed varying demands on conditional rule learning and working-with-memory operations that are essential for response selection. Damage to either structure impaired performance, but the respective deficits resulted from disruption of different processes. CN lesions produced a consistent learning deficit that was thought to reflect a basic impairment in forming stimulus-response (S-R) associations. The behavior of PFC rats was more variable and depended on task requirements. When S-R learning or response selection was relatively easy, the PFC was not critical. However, when either component was made more difficult, thus requiring the contribution of strategic processes, PFC damage produced profound impairments. In addition to clarifying the roles of the PFC and CN in CAL, the results provide further evidence that multiple brain regions participate in relatively simple behavioral tasks and that their respective contributions can be dissociated.

Hippocampal lesions alter conditioning to conditional and contextual stimuli

The control of conditioned fear behaviour by a conditional stimulus (CS) and contextual stimuli (CXT) was compared in rats with lesions to the hippocampus (HPC) or neocortex (CO), and operated controls (OC). After classical fear conditioning in a distinctive context, rats were subsequently tested in the presence of the CS and CXT (CS + CXT), the CS alone (CS-only), or context alone (CXT-only). Two experiments were conducted in which conditioned fear was measured by an active avoidance response (experiment 1) or by response suppression (experiment 2). Groups did not differ in acquiring the conditioned fear response, as measured in the CS + CON test but, in both experiments, hippocampal (HPC) groups exhibited more conditioned fear behaviour than controls in the CXT-Only and CS-Only conditions. It was suggested that control rats conditioned the fear response to a stimulus complex that incorporated the CS and CTX. Rats with HPC lesions did not form this association between the stimulus elements; instead they segregated the CS and CXT and formed independent associations between the conditioned response (CR) and each component. In showing that HPC damage disrupts the process of forming associations between environmental stimuli and that the effect is not restricted to contextual cues, the results help to resolve apparently contradictory findings regarding the role of HPC in contextual information processing.

Clustering and switching as two components of verbal fluency: evidence from younger and older healthy adults

Although verbal fluency is a frequently used neuropsychological test, little is known about the underlying cognitive processes. The authors proposed that 2 important components of fluency performance are clustering (i.e., the production of words within semantic or phonemic subcategories) and switching (i.e., the ability to shift between clusters). In Experiment 1, correlational data from 54 older and 41 younger adults indicated that both components were highly correlated with the number of words generated on semantic fluency, whereas switching was more highly correlated than clustering with the number of words generated on phonemic fluency. On semantic fluency, younger participants generated more words and switched more frequently than older participants; on phonemic fluency, older participants produced larger clusters than younger participants. In Experiment 2, among 22 young adults, divided attention decreased the number of words generated and decreased switching on phonemic fluency only. Overall, findings suggest that clustering and switching are dissociable fluency components and that switching is related to frontal-lobe functioning.

Correlation between frontal lobe functions and explicit and implicit stem completion in healthy elderly

The authors investigated the relationship between performance on neuropsychological tests, which were sensitive to medial-temporal and frontal lobe function, and implicit and explicit stem completion in a group of healthy elderly participants (mean age = 77.3 years). Several stem-completion conditions varying in the size of the search space and the specificity of the cues were included. Across conditions, performance on a frontal lobe sensitive test (word fluency) and on medial-temporal tests (California Verbal Learning Test; delayed recall) correlated with explicit stem completion. The correlations between frontal and medial-temporal test performance and implicit stem completion were weaker. However, a relationship was observed between frontal lobe functioning and stem completion when (a) the search space was large and the cues were constrained and (b) when the search space was limited and the cues were relatively unconstrained. Therefore, the role of the frontal lobes in implicit stem completion seems to be to detect bias resulting from prior study, and this involvement can only be revealed when the interaction between the size of the search space and the retrieval cues (a) makes bias detection necessary and (b) allows it to play a role. The stronger involvement of the frontal lobes in explicit stem completion likely reflects strategic retrieval processes, and the medial-temporal lobe involvement may be related to verification processes.

Cognitive impairment in rats fed high-fat diets: a specific effect of saturated fatty-acid intake

One-month-old rats were fed 1 of 4 high-fat diets (20% fat) or chow (4.5% fat) for 3 months. Dietary saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA) fatty acids varied such that their independent effects on cognitive performance could be tested. Rats were tested on a variable-interval delayed-alternation task. Impairment in both the ability to learn the basic alternation rule and remembering trial-specific information over time was observed in rats fed the experimental diets relative to those fed chow. The degree of impairment was highly associated with the level of SFAs fed and independent of the MUFAs or PUFAs. Dietary fat altered brain phosphatidylcholine fatty-acid profile, but the membrane changes did not correlate with cognitive impairment. The results demonstrate that cognitive impairment is directly associated with SFA intake but suggest that the mechanism is independent of bulk brain membrane compositional changes.

Clustering and switching as two components of verbal fluency: evidence from younger and older healthy adults

Although verbal fluency is a frequently used neuropsychological test, little is known about the underlying cognitive processes. The authors proposed that 2 important components of fluency performance are clustering (i.e., the production of words within semantic or phonemic subcategories) and switching (i.e., the ability to shift between clusters). In Experiment 1, correlational data from 54 older and 41 younger adults indicated that both components were highly correlated with the number of words generated on semantic fluency, whereas switching was more highly correlated than clustering with the number of words generated on phonemic fluency. On semantic fluency, younger participants generated more words and switched more frequently than older participants; on phonemic fluency, older participants produced larger clusters than younger participants. In Experiment 2, among 22 young adults, divided attention decreased the number of words generated and decreased switching on phonemic fluency only. Overall, findings suggest that clustering and switching are dissociable fluency components and that switching is related to frontal-lobe functioning.

Correlation between frontal lobe functions and explicit and implicit stem completion in healthy elderly

The authors investigated the relationship between performance on neuropsychological tests, which were sensitive to medial-temporal and frontal lobe function, and implicit and explicit stem completion in a group of healthy elderly participants (mean age = 77.3 years). Several stem-completion conditions varying in the size of the search space and the specificity of the cues were included. Across conditions, performance on a frontal lobe sensitive test (word fluency) and on medial-temporal tests (California Verbal Learning Test; delayed recall) correlated with explicit stem completion. The correlations between frontal and medial-temporal test performance and implicit stem completion were weaker. However, a relationship was observed between frontal lobe functioning and stem completion when (a) the search space was large and the cues were constrained and (b) when the search space was limited and the cues were relatively unconstrained. Therefore, the role of the frontal lobes in implicit stem completion seems to be to detect bias resulting from prior study, and this involvement can only be revealed when the interaction between the size of the search space and the retrieval cues (a) makes bias detection necessary and (b) allows it to play a role. The stronger involvement of the frontal lobes in explicit stem completion likely reflects strategic retrieval processes, and the medial-temporal lobe involvement may be related to verification processes.

Cognitive impairment in rats fed high-fat diets: a specific effect of saturated fatty-acid intake

One-month-old rats were fed 1 of 4 high-fat diets (20% fat) or chow (4.5% fat) for 3 months. Dietary saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA) fatty acids varied such that their independent effects on cognitive performance could be tested. Rats were tested on a variable-interval delayed-alternation task. Impairment in both the ability to learn the basic alternation rule and remembering trial-specific information over time was observed in rats fed the experimental diets relative to those fed chow. The degree of impairment was highly associated with the level of SFAs fed and independent of the MUFAs or PUFAs. Dietary fat altered brain phosphatidylcholine fatty-acid profile, but the membrane changes did not correlate with cognitive impairment. The results demonstrate that cognitive impairment is directly associated with SFA intake but suggest that the mechanism is independent of bulk brain membrane compositional changes.

Heightened interference on implicit, but not explicit, tests of negative transfer: evidence from patients with unilateral temporal lobe lesions and normal old people

The present research investigated alternative explanations of heightened interference in AB-AC learning in individuals with memory loss related to medial temporal lobe dysfunction. In Experiment 1, patients with left or right temporal lobectomy and control subjects were administered the standard AB-AC test. Relative to the other groups, left temporal patients exhibited significant negative transfer that was characterized by large numbers of response intrusion errors. In Experiment 2, groups of community-dwelling old and young adults were administered the standard test and an implicit version in which, during AC testing, subjects were instructed to provide the first word that comes to mind in response to stimulus words. There were no differences between groups on either version. Of particular interest was that both groups made significantly more intrusion errors on the implicit test and did not differ on this measure. It was concluded that exaggerated interference in AB-AC learning, as reflected by response intrusion errors, is related to the use of implicit memory processes rather than a failure of inhibitory mechanisms. Memory-impaired individuals, who have a selective loss of explicit memory, are vulnerable on this task because they rely excessively on implicit memory processes.

Dissociation of processes underlying spatial s-r compatibility: evidence for the independent influence of what and where

The process-dissociation procedure was used to estimate the influence of spatial and form-based processing in the Simon task. Subjects made manual (left/right) responses to the direction of arrows (> or <) presented to the left or right of fixation. Manipulating the proportion of incongruent trials (e.g., a right-pointing arrow presented to the left of fixation) affected both the size and direction of the Simon effect. To account for this pattern of data, we compared process estimates based on three possible relationships between spatial and form-based processing: independence, redundancy, and exclusivity. The independence model provided the best account of the data. Most telling was that independent form-based estimates were superior at predicting observed performance on arrows presented at fixation and did so consistently across conditions (r's > .80). The results provide evidence that the form ("what") and spatial location ("where") of a single stimulus can have functionally independent effects on performance. They also indicate the existence of two kinds of automaticity--an associative ("implicit learning") component that reflects prior S-R mappings and a nonassociative component that reflects the correspondence between stimulus and response codes.

Dissociation of pathways for object and spatial vision: a PET study in humans

A positron emission tomography (PET) study was conducted to determine which brain regions are differentially involved in visual object identification and object localization. Subjects engaged in a spatial task in which they matched the location of common objects, and an object task in which they matched the identity of common objects. In both tasks the stimulus arrangements used were of the same kind. Regional cerebral blood flow data showed that a right-sided region in the inferior parietal lobule was more activated during spatial than during object matching. In contrast, bilateral occipitotemporal regions, with the left more predominant, were more activated during object than spatial matching. These results provide support for Ungerleider and Mishkin's dual pathway model of vision and indicate important patterns of lateralization in the human visual system.

Intact visual imagery and impaired visual perception in a patient with visual agnosia

Although it is now well accepted that visual mental imagery and visual perception share common underlying mechanisms, there are several reports in which they are dissociated. Evidence for the separability of these processes is provided by a patient, C.K., who has a profound visual object recognition deficit attributable to an impairment in grouping or segmenting visual images. Despite this perceptual deficit, C.K. was able to draw objects in considerable detail from memory, and his knowledge of the visual appearance of objects was preserved on a variety of mental imagery tasks. Together with previous cases, these findings confirm the double dissociation between object recognition and perception. Interestingly, C.K. could also recognize newly constructed objects in his internal imagery. To accommodate these results, we propose a model in which imagery and perception are strongly associated but are also functionally specialized.

Intact visual imagery and impaired visual perception in a patient with visual agnosia

Although it is now well accepted that visual mental imagery and visual perception share common underlying mechanisms, there are several reports in which they are dissociated. Evidence for the separability of these processes is provided by a patient, C.K., who has a profound visual object recognition deficit attributable to an impairment in grouping or segmenting visual images. Despite this perceptual deficit, C.K. was able to draw objects in considerable detail from memory, and his knowledge of the visual appearance of objects was preserved on a variety of mental imagery tasks. Together with previous cases, these findings confirm the double dissociation between object recognition and perception. Interestingly, C.K. could also recognize newly constructed objects in his internal imagery. To accommodate these results, we propose a model in which imagery and perception are strongly associated but are also functionally specialized.

Intact primary memory in mild to moderate Alzheimer disease: indices from the California Verbal Learning Test

The California Verbal Learning Test (CVLT; Delis, Kramer, Kaplan, & Ober, 1987) was administered to patients with mild to moderate Alzheimer disease (AD) (Group AD; n = 13) and to a control group of normal older adults (Group NC; n = 13) matched on age and education. Two measures were used to determine whether primary memory (PM) is impaired in early AD. One measure, considered a relatively "pure" measure of PM, is based on the procedure developed by Tulving and Colotla (1970) which considers an item to be recalled from PM if no more than six items intervene between its presentation and recall. The other measure is the more commonly used recall from recency. No significant difference between the AD and NC Groups was found, both on the Tulving and Colotla measure, as well as on the recall from recency measure of PM. A significant difference was obtained on two measures of secondary memory (SM), namely, Tulving and Colotla's measure and recall from the primacy and middle regions of the list of words. In comparison to NC, and AD patients showed little evidence of learning over the five trials, and poor retention even over short delays. In addition, the patients with AD showed deficits in clustering words by taxonomic category at recall. We conclude that impairment in PM cannot be used as a diagnostic marker of AD in the early stages of the disease process.

Dissociation between mental imagery and object recognition in a brain-damaged patient

Visual imagery is the creation of mental representations that share many features with veridical visual percepts. Studies of normal and brain-damaged people reinforce the view that visual imagery and visual perception are mediated by a common neural substrate and activate the same representations. Thus, brain-damaged patients with intact vision who have an impairment in perception should have impaired visual imagery. Here we present evidence to the contrary from a patient with severely impaired object recognition (visual object agnosia) but with normal mental imagery. He draws objects in considerable detail from memory and uses information derived from mental images in a variety of tasks. In contrast, he cannot identify visually presented objects, even those he has drawn himself. He has normal visual acuity and intact perception of equally complex material in other domains. We conclude that rich internal representations can be activated to support visual imagery even when they cannot support visually mediated perception of objects.

A comparison of normal old rats and young adult rats with lesions to the hippocampus or prefrontal cortex on a test of matching-to-sample

Rats with lesions to the dorsal hippocampus (HPC) or prefrontal cortex (PFC), normal old rats, and young adult controls were compared on a test of matching-to-sample. Subjects were presented with two lights in succession and were trained to press a lever when the lights were the same brightness and withhold a lever-press when they were different. The PFC and aged groups, but not the HPC group, were impaired when the comparison stimulus was presented immediately after the sample stimulus. When delays of 5 and 15 sec were introduced between the stimuli, the HPC and aged groups' performance deteriorated to chance levels. The PFC group's performance was not differentially affected by the delays. The results were consistent with previous findings that implicated the HPC in episodic memory and the PFC in working memory. The aged group was impaired on both types of memory, revealing signs of HPC and PFC dysfunction.

Conditional learning in aged rats: evidence of hippocampal and prefrontal cortex impairment

Groups of normal old rats and young adult rats were administered a test of conditional discrimination learning in which different visual stimuli were associated with responses to different levers. Initially, rats were tested in a zero-delay condition in which they selected their responses in the presence of the conditional stimuli. They were later tested at 5- and 15-s delays between stimulus presentation and the appearance of the levers. Old rats were impaired in learning the basic conditional discrimination, a test thought to be sensitive to frontal lobe dysfunction. Age differences increased with the length of the interval, revealing a time-dependent memory loss that was attributed to impaired hippocampal function.