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Behavioural evaluation of workers exposed to mixtures of organic solvents.

Reports from Scandinavia have suggested behavioural impairment among long term workers exposed to solvents below regulatory standards. A cross sectional study of behavioural performance was conducted among printers and spray painters exposed to mixtures of organic solvents to replicate the Scandinavian studies and to examine dose-response relationships. Eligible subjects consisted of 640 hourly workers from four midwestern United States companies. Of these, 269 responded to requests to participate and 240 were selected for study based on restrictions for age, sex, education, and other potentially confounding variables. The subjects tested had been employed on average for six years. Each subject completed an occupational history, underwent a medical examination, and completed a battery of behavioural tests. These included the Fitts law psychomotor task, the Stroop colour-word test, the Sternberg short term memory scanning test, the short term memory span test, and the continuous recognition memory test. Solvent exposure for each subject was defined as an exposed or non-exposed category based on a plant industrial hygiene walk-through and the concentration of solvents based on an analysis of full shift personal air samples by gas chromatography. The first definition was used to maintain consistency with Scandinavian studies, but the second was considered to be more accurate. The average full shift solvent concentration was 302 ppm for the printing plant workers and 6-13 ppm for the workers at other plants. Isopropanol and hexane were the major components, compared with toluene in Scandinavian studies. Performance on behavioural tests was analysed using multiple linear regression with solvent concentration as an independent variable. Other relevant demographic variables were also considered for inclusion. No significant (p greater than 0.05) relation between solvent concentration and impairment on any of the 10 behavioural variables was observed after controlling for confounding variables. Exposed/non-exposed comparisons showed a significantly poorer digit span among those exposed, but this has not been generally reported in the Scandinavian studies. The medical examination showed no abnormalities of clinical significance. The inability to replicate the findings of the Scandinavian studies could have been due to the shortness of the duration of workers' exposure, the type of solvents in the mixtures, use of different behavioural tests, or to selection factors.

Adult↗

Differing patterns of temporal atrophy in Alzheimer's disease and semantic dementia.

OBJECTIVE: To characterize and quantify the patterns of temporal lobe atrophy in AD vs semantic dementia and to relate the findings to the cognitive profiles. Medial temporal lobe atrophy is well described in AD. In temporal variant frontotemporal dementia (semantic dementia), clinical studies suggest polar and inferolateral temporal atrophy with hippocampal sparing, but quantification is largely lacking. METHODS: A volumetric method for quantifying multiple temporal structures was applied to 26 patients with probable AD, 18 patients with semantic dementia, and 21 matched control subjects. RESULTS: The authors confirmed the expected bilateral hippocampal atrophy in AD relative to controls, with involvement of the amygdala bilaterally and the right parahippocampal gyrus. Contrary to expectations, patients with semantic dementia had asymmetric hippocampal atrophy, more extensive than AD on the left. As predicted, the semantic dementia group showed more severe involvement of the temporal pole bilaterally and the left amygdala, parahippocampal gyrus (including the entorhinal cortex), fusiform gyrus, and the inferior and middle temporal gyri. Performance on semantic association tasks correlated with the size of the left fusiform gyrus, whereas naming appeared to depend upon a wider left temporal network. Episodic memory measures, with the exception of recognition memory for faces, did not correlate with temporal measures. CONCLUSIONS: Hippocampal atrophy is not specific for AD but is also seen in semantic dementia. Distinguishing the patients with semantic dementia was the severe global but asymmetric (left > right) atrophy of the amygdala, temporal pole, and fusiform and inferolateral temporal gyri. These findings have implications for diagnosis and understanding of the cognitive deficits in AD and semantic dementia.

Aged↗

Scopolamine reduces persistent activity related to long-term encoding in the parahippocampal gyrus during delayed matching in humans.

Recent computational modeling and slice physiology studies have suggested that long-term encoding may depend on sustained spiking during brief memory delays in parahippocampal neurons, and that this persistent spiking activity is modulated by effects of acetylcholine at muscarinic receptors. Our recent functional magnetic resonance imaging (fMRI) study has shown that sustained parahippocampal delay period activity during delayed match-to-sample performance in healthy young individuals predicted subsequent memory of visual stimuli on a recognition memory assessment 20 min later (Schon et al., 2004). The current study combined this fMRI paradigm with a pharmacological manipulation to test whether this long-term encoding-related delay activity is reduced in subjects who receive the muscarinic cholinergic antagonist scopolamine before fMRI scanning. Subsequent memory was predicted by sustained activity during brief memory delays bilaterally in the perirhinal/entorhinal cortex, in the right posterior parahippocampal and mid-fusiform gyri, and in the hippocampal body in healthy young individuals without a scopolamine challenge. This activity was reduced in subjects receiving scopolamine. The results are consistent with computational modeling data and behavioral pharmacological studies, suggesting that long-term encoding-related activity may be reduced if cholinergic receptors are blocked by scopolamine.

Analysis of Variance↗

[Neuropsychological changes and bilateral subthalamic deep brain stimulation in Parkinson's disease].

INTRODUCTION: To investigate neuropsychiatric changes in Parkinson's disease (PD) patients after 12 months of bilateral subthalamic deep brain stimulation (DBS-STN). SUBJECTS: Nine out of 23 patients with PD subjected to DBS-STN were included. The mean follow-up of this cohort was 12 months, mean disease duration 14.2 5.5 years and mean UPDRS motor score in < > 43.2 13.7. METHODS: Patients were selected on the basis of CAPSIT criteria. They underwent bilateral implant of stimulators in STN under stereotactic conditions. Quality of life scale (PDQ 39), depression scale (Brev-Cet), frontal function test (Stroop, Wisconsin, verbal fluency) and memory evaluation (Barcelona test) were monitored at baseline in < > medication and after 12 months in < > medication/< > stimulation. RESULTS: The patients' motor scores improved on an average of 40.2 % (p = 0.0002) in < > medication situation and 58 % in quality of life scores. We observed a benefit in depression scores (52 %, p = 0.003). Immediate verbal memory improved as well, 25 % (p = 0.04) in recall memory and 14 % (p = 0.02) in recognition memory. No changes were observed in visual memory, verbal fluency and/or global cognitive tests. CONCLUSION: DBS-STN in PD patients seems to be an effective tool for improving their quality of life, due to its benefits on motor function, verbal memory and mood. Bilateral DBS-STN did not affect either verbal fluency or executive functions in our patients. Neuropsychological assessment is a good tool for selection and study of the operated patients.

Activities of Daily Living↗

The effect of anticipation and the specificity of sex differences for amygdala and hippocampus function in emotional memory.

Prior research has shown memory is enhanced for emotional events. Key brain areas involved in emotional memory are the amygdala and hippocampus, which are also recruited during aversion and its anticipation. This study investigated whether anticipatory processes signaling an upcoming aversive event contribute to emotional memory. In an event-related functional MRI paradigm, 40 healthy participants viewed aversive and neutral pictures preceded by predictive warning cues. Participants completed a surprise recognition task directly after functional MRI scanning or 2 weeks later. In anticipation of aversive pictures, bilateral dorsal amygdala and anterior hippocampus activations were associated with better immediate recognition memory. Similar associations with memory were observed for activation of those areas in response to aversive pictures. Anticipatory activation predicted immediate memory over and above these associations for picture viewing. Bilateral ventral amygdala activations in response to aversive pictures predicted delayed memory only. We found that previously reported sex differences of memory associations with left amygdala for women and with right amygdala for men were confined to the ventral amygdala during picture viewing and delayed memory. Results support an established animal model elucidating the functional neuroanatomy of the amygdala and hippocampus in emotional memory, highlight the importance of anticipatory processes in such memory for aversive events, and extend neuroanatomical evidence of sex differences for emotional memory.

Adult↗

Age-related changes in memory reactivation by 1- and 2-year-old human infants.

In three experiments, we examined the effect of a single reactivation treatment on retention by 1- and 2-year-old human infants who were tested in the visual recognition memory (VRM) paradigm. In all experiments, infants were familiarized with a visual stimulus and were tested after a delay. In the absence of a reactivation treatment, infants of both ages exhibited forgetting but exposure to a reactivation treatment alleviated forgetting after the same delay. When the duration of the original familiarization period was only 10 s, the minimum duration of an effective reminder treatment was 1 s for 2-year-olds, but was 5 s for 1-year-olds. When the duration of the original familiarization period was increased to 30 s, however, a 1-s reminder also alleviated forgetting by 1-year-olds.

Age Factors↗

Memory impairment on a delayed non-matching-to-position task after lesions of the perirhinal cortex in the rat.

Previous research conducted in monkeys and rats has established that the perirhinal cortex is critically involved in object- or stimulus-recognition memory, whereas other research suggests this region may contribute to memory for object discriminations. These findings do not rule out the possibility that the perirhinal cortex plays a more general role in memory. The present experiment addressed whether selective lesions of the perirhinal cortex would result in a delay-dependent deficit on a test of memory that did not involve stimulus recognition or object memory. Rats with bilateral perirhinal lesions were tested on a delayed non-matching-to-position task. Lesions of the perirhinal cortex did not interfere with acquisition or performance at short (0-4 s)-delay intervals, but lesions did impair performance at longer delays. It is suggested that the perirhinal cortex is involved in maintaining representations of trial-specific information over time.

Analysis of Variance↗

Detecting simulated amnesia for autobiographical and recently learned information using the P300 event-related potential.

To investigate whether the P300 (P3) event-related potential (ERP) can be used as an index of the intactness of recognition memory in subjects trying to simulate amnesia, two groups of subjects (n = 12 and n = 15) were instructed to simulate amnesia and one group of control subjects (n = 14) did not simulate amnesia while taking three recognition tests, during which ERPs were recorded. The three tests consisted of three different types of memory items: (1) the subject's birthday (birth), (2) the experimenter's name (name), (3) a word list of 14 nouns (words). The memory item was presented in a random series with other, similar in type, non-memory items. In group tests, memory items evoked larger amplitude P3s than non-memory items (p < 0.001). Within-subjects tests were used to determine whether the P3 amplitude in response to memory items was larger than the P3 amplitude in response to non-memory items for each individual. There was no difference between the sensitivity of the best within-subjects tests for amnesia simulators (birth = 0.9, name = 0.85, words = 0.53) versus non-simulators (birth = 1.0, name = 0.81, words = 0.5) averaged across the three test types. This suggests that P3 used as an index of the intactness of recognition memory may be useful in cases of suspected malingering.

Adult↗

Hippocampal damage equally impairs memory for single items and memory for conjunctions.

In a prior study of continuous recognition performance, data were reported in support of the hypothesis that the hippocampus is not needed to remember the individual components of a stimulus but is important for remembering associations between its components (Kroll et al. 1996. J Mem Lang 35:176-196). Patients with left hippocampal damage were able to endorse recently encountered words and to reject novel words, as well as disyllabic words in which one of the syllables had been previously encountered. However, they failed to reject words in which both syllables had been encountered independently in different words. We present data from five experiments designed to examine this finding in more detail. In each experiment, five patients with bilateral hippocampal damage and eight controls were tested using the same protocol as Kroll et al. (1996). On each trial, a two-component stimulus was presented. Stimuli could be entirely novel, novel with one previously encountered (repeated) component, novel but with both components repeated, or a true repetition. The first experiment was a direct replication using the same disyllabic words as Kroll et al. (1996). The second experiment used pseudo-words, constructed of two monosyllabic words (e.g., jambark). The third experiment used the same pairs of monosyllabic words, but presented separately on the screen to encourage participants to treat each component independently. The fourth experiment used pairs of objects, and the fifth experiment used face-house pairs. In all five experiments, patients with hippocampal damage exhibited impaired recognition memory. The impairment extended across all trial types with no evidence that hippocampal damage selectively (or disproportionately) impaired the associative or conjunctive component of memory. We discuss our findings in the light of the work by Kroll et al. (1996) and other recent neuropsychological, electrophysiological, and neuroimaging studies of hippocampal function and single-item and associative memory.

Adult↗

Making memories without trying: medial temporal lobe activity associated with incidental memory formation during recognition.

Structures in the medial portions of the human temporal lobes (MTL) play a vital role in the ability to learn new facts and events, whether such learning is intentional or incidental. We examined neural activity in the MTL both while participants studied pictures of novel scenes and while they attempted to recognize which scenes had been previously presented. In a second surprise test we assessed participants' memory for items that were presented only during the previous recognition memory test. We present a novel approach to cross-participant alignment of neuroimaging data that provides more precise localization and enhanced statistical power within regions such as the MTL. Using this technique, we observed that the amount of MTL activity predicted participants' ability to subsequently remember scenes not only during the intentional study task, but also during the first memory retrieval test when only incidental encoding occurred. This encoding-related activity during memory retrieval was in the same subregions of the MTL as encoding-related activity during intentional study and is hypothesized to be one of the primary reasons why retrieval-related activity is often difficult to observe with neuroimaging techniques.

Adolescent↗

Effect of task demands on dual coding of pictorial stimuli.

Recent studies have suggested that verbal labeling of a picture does not occur automatically. Although several experiments using paired-associate tasks produced little evidence indicating the use of a verbal code with picture stimuli, the tasks were probably not sensitive to whether the codes were activated initially. It is possible that verbal labels were activated at input, but not used later in performing the tasks. The present experiment used a color-naming interference task in order to assess, with a more sensitive measure, the amount of verbal coding occurring in response to word or picture input. Subjects named the color of ink in which words were printed following either word or picture input. If verbal labeling of the input occurs, then latency of color naming should increase when the input item and color-naming word are related. The results provided substantial evidence of such verbal activation when the input items were words. However, the presence of verbal activation with picture input was a function of task demands. Activation occurred when a recall memory test was used, but not when a recognition memory test was used. The results support the conclusion that name information (labels) need not be activated during presentation of visual stimuli.

Attention↗

Perceptual and conceptual training mediate the verbal overshadowing effect in an unfamiliar domain.

Describing memory for a nonverbal perceptual stimulus can impair recognition. This verbal overshadowing effect may occur when perceptual expertise exceeds verbal expertise, but previous evidence for this hypothesis has been strictly correlational. We conducted two experiments, exploring the relation between expertise and verbal overshadowing by manipulating perceptual and conceptual knowledge. Participants received perceptual training (categorizing mushrooms), conceptual training (lecture), or no training, then viewed a mushroom and described it or not. A recognition test followed. In Experiment 1, perceptual training increased susceptibility to verbalization relative to the no training condition. However, conceptual training did not insulate individuals from the verbal overshadowing effect. Experiment 2 was modified to enhance both forms of training. It replicated the finding that perceptual training increases vulnerability to verbal overshadowing, and indicated that, when sufficiently emphasized, verbalization may be useful following conceptual training. The results demonstrate the role that different forms of learning and expertise may play in mediating language influences on recognition memory.

Humans↗

An event-related potential study of the revelation effect.

Event-related potentials (ERPs) were recorded during a verbal recognition memory task in order to investigate whether changes in familiarity are part of the explanation for the revelation effect. For half of the test words, participants solved an anagram prior to making the old/new recognition judgment. A revelation effect was obtained: When test words were preceded by the anagram task, a higher probability of an old response was associated with the items than was otherwise the case. The ERPs recorded time-locked to the onset of the test words were separated according to old/new status andthe presence/absence of the anagram task. The ERP index of familiarity was of lower amplitude for both old and new items that were preceded by the anagram task. These findings are consistent with the view that part of the explanation for the revelation effect is a reduction in the familiarity of the critical test items.

Adolescent↗

Construct validity of the Continuous Visual Memory Test.

The construct validity of the Continuous Visual Memory Test (CVMT), a new measure of visual recognition memory was evaluated based on the performance of 92 healthy, normal adults. A series of factor analyses were conducted utilizing marker variables for verbal memory, visual memory, attention and concentration, and verbal and visual/nonverbal intellectual functions. CVMT acquisition scores were associated with verbal and visual/nonverbal intellectual factors as well as with attentional ability. The CVMT delayed recognition score was shown to be a factorially "pure" measure of visual memory.

Journal Article↗

Use of a false recognition paradigm in an Alzheimer's disease clinical trial: a pilot study.

We report the first use of a false recognition memory test in a clinical trial of patients with Alzheimer's disease (AD). Tests of false recognition allow measurement of two components of memory: the specific details of a prior encounter with a particular item (item-specific recollection) and the general meaning, idea, or gist conveyed by a collection of items (gist memory). We used a false recognition paradigm with categorized pictures to study the effects of an experimental medication in patients with AD. Because medications to treat AD may preferentially improve gist memory or item-specific recollection, use of this type of paradigm may improve sensitivity for detection of drug effects more than standard memory tests.

Aged↗

Visual imagery in recognition and source memory for audiotape and text.

80 participants heard an audiotape of a crime, read an account with both correct and new information, then took recognition and source memory tests. While listening and reading, participants attended carefully, and half also formed visual images of the events. Imagery instructions had no effects, but recognition memory was better for material from the text only than from the audiotape only, whereas source memory was better for audiotape than for text. These results replicate previous findings for film and audiotape.

Adult↗

Intact perceptual memory in the absence of conscious memory.

Declarative memory enables conscious recollection of the past and has been proposed to be distinct from priming, a perceptual form of memory that operates nonconsciously and improves the ability to detect or identify recently presented stimuli. Yet, it has been difficult to obtain unambiguous evidence for the independence of declarative memory and priming. The authors report the first demonstration, using matched tests, of fully intact perceptual memory (priming) in a profoundly amnesic patient (E.P.), despite at-chance recognition memory. The priming and recognition tests included tests that were matched with respect to test materials, length of the study and test lists, and the kind of cues available at test. Priming appears to reflect neural changes within perceptual processing systems that occur before information reaches the brain systems that transform visual perception into conscious visual memory.

Aged↗

ERP recordings during a picture fragment completion task: effects of memory instructions.

Sequential implicit (picture fragment completion) and explicit (free recall and recognition) memory tasks were performed by two groups of young adults. Subjects assigned to the intentional condition were asked to memorize the stimuli presented during the picture fragment completion task, whereas subjects assigned to the incidental condition were not so instructed. In the picture fragment completion task, all subjects showed savings (priming), i.e., their identification thresholds for previously seen fragments were lower than those for fragments not previously seen, and no between-group performance difference was found. Free recall performance was better for the intentional than the incidental group, but recognition performance did not differ between the groups. Despite similar between-group performance, event-related brain potentials (ERPs) recorded during the picture fragment completion and recognition tasks revealed between-group differences in information processing. The ERP data suggest that similar behavioral performance during memory tasks may have been associated with distinct neuronal mechanisms subserving priming and recollection.

Adult↗