Do PETS have long or short ears? Mental imagery and neuroimaging.
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Brain↗
Biomedical subjects
G Winocur
Publications and source records attributed to G Winocur.
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.
Adult↗
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.
Aged↗
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.
Adult↗
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.
Aging↗
Anterograde and retrograde amnesia in rats with dorsal hippocampal or dorsomedial thalamic lesions.
The present research was concerned with anterograde and retrograde memory for a socially transmitted food preference in rats with lesions to the dorsal hippocampus or dorsomedial thalamus, and operated controls. In Expt. 1, food-preference training was administered postoperatively and memory was tested following various delays. Both lesioned groups acquired the preference normally, but rats with hippocampal lesions displayed a rapid rate of forgetting that indicated significant anterograde amnesia. In Expt. 2, the food preference was acquired at different times preoperatively and retrograde memory was tested postoperatively. Both lesioned groups exhibited loss of memory when training immediately preceded surgery, but only rats with hippocampal lesions displayed a temporally-graded retrograde amnesia. The results confirmed the differential effects of hippocampal and thalamic lesions on memory performance. It was suggested that memory loss following thalamic lesions was related to factors associated with original learning, whereas the pattern of hippocampal amnesia reflected disruption at a later stage in the learning process.
Animals↗
Learning and memory impairment in rats fed a high saturated fat diet.
At the age of 1 month, three separate groups of Long-Evans rats were placed on 20% (w/w) fat (40% of calories) diets high in either saturated fatty acids (lard-based) or polyunsaturated fatty acids (soybean oil-based) or standard laboratory chow (Purina, 4.5% (w/w) fat). After 3 months, all rats were administered three tests of learning and memory--Olton's radial arm maze, a variable-interval delayed alternation task, and the Hebb-Williams maze series. The lard-fed group was impaired on all tests. The soybean oil-fed group was slightly impaired on some measures, relative to the chow-fed group, but consistently performed better than the lard-fed group. The results indicate that a diet high in saturated fatty acids can impair a wide range of learning and memory functions and are in line with biochemical and physiological evidence showing widespread effects of such diets on brain function.
Animals↗
Hippocampal and prefrontal cortex contributions to learning and memory: analysis of lesion and aging effects on maze learning in rats.
Young adult rats with bilateral lesions to the hippocampus or prefrontal cortex, young operated controls, and normal old rats were tested on two complex mazes in the Hebb-Williams series. Approximately half the animals were previously trained on one of the mazes; the remainder received no previous training. The trained hippocampal rats showed sparing of memory for the general skill of maze learning but poor recall of the specific maze on which they had been previously trained. The opposite pattern was observed in trained prefrontal rats. In contrast, the aged rats' memory for maze-specific and maze-general information was impaired. The results confirmed the importance of the hippocampus for recalling highly specific information and pointed to a possible role for the frontal lobes in learning and remembering nonspecific skill-related information. The generalized deficit of the aged rats indicates that both types of memory were compromised and offers further evidence of frontal lobe and hippocampal dysfunction in normal aging.
Aging↗
A comparison of cognitive function in community-dwelling and institutionalized old people of normal intelligence.
Two carefully matched groups of normal old people living in institutions or in the community were administered a neuropsychological cognitive test battery. In general, the institutionalized group performed worse than the community group. Discriminant function analysis identified a subgroup of high-functioning institutionalized subjects whose performance more closely resembled that of the community group than the remainder of the institutionalized group. Differences between the various groups were not due to differences in IQ, age, health, or other controlled variables. The critical tests that differentiated the groups were sensitive to impaired function in frontal and medial-temporal lobe brain regions. The results suggest a complex interaction involving effects of age and environmental factors on brain function and cognition.
Aged↗
Long-term memory loss in senescent rats: neuropsychological analysis of interference and context effects.
Four experiments are reported in which normal, senescent (25-27 months) and young adult (6 months) rats were tested for recall of a passive avoidance response 1 hr or several weeks after conditioning. There were no age differences at the 1-hr test, but a decrement was observed in old rats tested under standard conditions after long delays. The age-related impairment was exaggerated when additional approach training was administered in an identical apparatus between avoidance conditioning and testing. When the approach training was administered in an apparatus that contrasted markedly from the original, no age differences were observed. It was concluded that increased susceptibility to interference and contextual factors contributed to rapid forgetting in old rats, a pattern very similar to that observed previously in young adult rats with selective lesions to the hippocampus.
Aging↗
Contextual cuing and memory performance in brain-damaged amnesics and old people.
In Experiment 1, groups of Korsakoff amnesics and alcoholic controls learned a list of paired-associate words in a standard testing room or in a room with distinctive contextual features. Recall was tested 48 hr later in the same or other context. This procedure was repeated in Experiment 2 with old people living in institutions or in the community, but matched for age, health, education, and socioeconomic background. The amnesic patients and institutionalized old people, relative to their comparison groups, were more impaired in recalling the lists under standard conditions and were more responsive to contextual cuing, especially when the distinctive cues were provided during original learning. The results highlight the susceptibility to interference of Korsakoff amnesics and institutionalized old people and offer further evidence that both groups are more responsive to salient contextual cues than either young people or old people living in the community.
Aged↗
The hippocampus and conditioning to contextual cues.
Two experiments are reported in which behavioral control by contextual cues was assessed in groups of rats with dorsal hippocampal (HC), neocortical (NC), or operated control (OC) lesions. Following Odling-Smee's (1975) procedure, a Pavlovian conditioning paradigm was followed in which conditioned stimuli (CSs: tone, light) predicted an unconditioned stimulus (US:footshock) always, never, or half the time. Conditioning trials took place in a small black box. Subsequently, conditioning to background contextual cues was assessed by measuring the amount of time rats spent in the black box in preference to an adjacent white one with neither CS nor US presented. In OC groups and, to a lesser extent, NC groups, conditioning to background cues was inversely related to the probability that CS predicted US. In contrast to graded contextual conditioning in control groups, the HC groups consistently showed abnormally strong conditioning to context that was at or near asymptotic level. The results, which were related to current theories of the relation between contextual stimuli and CSs, suggest that the hippocampus may play an important role in stimulus selection during learning.
Animals↗
An investigation of cognitive function in relation to psychosocial variables in institutionalized old people.
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Aged↗
Memory as assessed by recognition and reading time in normal and memory-impaired people with Alzheimer's disease and other neurological disorders.
Three experiments are reported that examine the dissociations in performance on two tests of retention, speeded reading and recognition in young people, home-dwelling and institutionalized elderly people, and people with severe memory disorders. In Experiment 1, subjects read sentences in normal and in geometrically transformed script at initial presentation, 1-2 hr later, and again 4-14 days later. On the latter two occasions, they were required to distinguish old sentences that they had read previously from new ones. In general, the young and elderly subjects could distinguish old from new sentences at the short delay, and all but the institutionalized elderly people could do so at the long delay. Retention as measured by reading speed typically paralleled recognition performance in that those items that were recognized best were read most quickly. The dissociation between these two tests of retention is seen only in people with memory disorders. Although these people could not distinguish old from new items even at short delays (most could not even remember having seen any sentences), their retention as assessed by reading time was similar to that of the other groups. Old sentences were read most quickly, indicating retention of item-specific information, and reading time of new sentences improved, indicating the acquisition and retention of a general skill. Experiment 2 examined what type of item-specific information was retained. Young, elderly, and memory-disordered subjects studied weakly associated word pairs and sentences. A few minutes later they were tested on both recognition and speeded reading of old, new, and recombined pairs and sentences, the last being those in which words from a studied pair or sentence were recombined with words from other such pairs or sentences. The results of both retention tests indicated that young and elderly people could distinguish old from new and recombined items. People with memory disorders, however, again failed on recognition but performed normally on speeded reading. Like the other two groups, they read old items faster than either recombined or new items. In Experiment 3, similar results were obtained even when the word pairs were constructed using randomly associated items. The results of all three experiments suggest that on implicit tests of memory, such as speeded reading, people with memory disorders can be shown to have formed and retained new associations despite failing utterly on explicit tests, such as recognition, that require conscious recollection of a previous episode.(ABSTRACT TRUNCATED AT 400 WORDS)
Aged↗
Memory decline in aged rats: a neuropsychological interpretation.
Groups of old and young rats were administered a delayed alternation task in which memory for specific events was assessed over intervals ranging between 0 and 80 s. There was no age difference in performance at relatively short intervals, but old rats showed significant memory loss at longer intervals. The pattern of behavior exhibited by old rats was very similar to that seen in young rats with selective hippocampal lesions, tested in a previous experiment under identical conditions. The present results were interpreted as reflecting an integrative deficit in old animals related to the process of establishing and/or storing associations between temporally-separated events.
Aging↗
The hippocampus and thalamus: their roles in short- and long-term memory and the effects of interference.
Rats with dorsal hippocampal, dorsomedial thalamic, and operated control lesions were administered a delayed alternation (DA) task in which recall was assessed over intervals ranging between 0 and 80 s, and a passive avoidance (PA) task, involving training-test delays of between 1 h and 21 days. On both tasks, hippocampal groups performed normally at relatively short intervals, but showed significant memory loss at longer intervals. Thalamic groups were generally impaired on the DA task, but performed as well as operated control groups at all intervals in the PA task. The data also indicated an exaggerated susceptibility to interference in the hippocampal groups and a loss of episodic and reference memory following hippocampal or thalamic lesions. Similarities between the performance of rats with hippocampal or thalamic lesions and comparably brain-damaged human amnesics were noted. In line with current hypotheses, it was concluded that memory loss following thalamic damage is related to a deficit in the early stages of new learning, whereas hippocampal amnesia results from impairment at a later, integrative stage in which long-term memories are formed and durably stored.
Animals↗
The effects of retroactive and proactive interference on learning and memory in old and young rats.
The effects of interference on learning and memory in old and young rats were compared using a visual discrimination task. In Experiment I, discrimination training was followed by one of three interference treatments and finally by retesting on the discrimination task. There were no age differences in original learning but old rats were significantly impaired in remembering the visual discrimination when a high-interference treatment involving similar stimuli was introduced between original learning and retesting. In Experiment II, old rats were impaired on discrimination learning when the high-interference treatment was administered before discrimination training. Analysis of response patterns showed that the exaggerated susceptibility of old rats to interference effects resulted in a general behavioral inflexibility similar to that observed in young adult rats with damage to the hippocampal region.
Aging↗
Dorsal bundle lesions do not affect latent inhibition of conditioned suppression.
Three experiments are reported which examine the effects of lesions of the dorsal ascending noradrenergic bundle (DB) on latent inhibition using a conditioned suppression procedure in rats. In none of the experiments did the DB lesion have any effect, despite changes in the extent of latent inhibition and in the control procedures used to assess it. The results are discussed in relation to the attentional theory of DB function.
Animals↗