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PubMed2006

Gradual translocation of spatial correlates of neuronal firing in the hippocampus toward prospective reward locations.

In a continuous T-maze alternation task, CA1 complex-spike neurons in the hippocampus differentially fire as the rat traverses overlapping segments of the maze (i.e., the stem) repeatedly via alternate routes. The temporal dynamics of this phenomenon were further investigated in the current study. Rats learned the alternation task from the first day of acquisition and the differential firing pattern in the stem was observed accordingly. More importantly, we report a phenomenon in which spatial correlates of CA1 neuronal ensembles gradually changed from their original firing locations, shifting toward prospective goal locations in the continuous T-maze alternation task. The relative locations of simultaneously recorded firing fields, however, were preserved within the ensemble spatial representation during this shifting. The within-session shifts in preferred firing locations in the absence of any changes in the environment suggest that certain cognitive factors can significantly alter the location-bound coding scheme of hippocampal neurons.

Animals↗

PubMed1991

Task coordination in human prehension.

Movement patterns may be complex in the sense of being composed of separable component tasks. These components may be coordinated at some level by the voluntary motor system, in order to combine tasks into appropriate actions. This study describes the use of task interference methods and phase transition curves (PTCs) to quantify task interference in tasks that may have two components. Comparison of the effects of task interference on the different components suggests how these may be coordinated during normal movements. These techniques can be applied to the coordination of hand transport and grasp aperture components in the reaching and grasping movements that people make in order to pick things up. Five subjects made cyclical movements that involved either composite reaching or just the transport or grasp component in isolation, according to condition. The cyclical movements were "perturbed" by requiring a rapid transport or grasping response to an auditory signal by the contralateral hand. The pattern of phase shifts, or changes in the timing of the cyclical task introduced by these perturbations was modeled using phase transition curves, in order to assess the nature of the functional linkage between transport and aperture in normal prehensile movement. The results suggest a functional linkage between grasp aperture and hand transport in normal prehensile movement.

Journal Article↗

PubMed1997

Effects of tobacco smoking and gender on interhemispheric cognitive function: performance and confidence measures.

Cognitive function in tasks involving interhemispheric processing of verbal and spatial information was studied in 31 college students in a 2 x 2 factorial design with chronic smoking status [smoker (10+ cigarettes per day) versus non-smoker (no history of smoking)] and gender as the main between-subject factors. The subjects participated in two sessions on two consecutive days. The same task was repeated within the same session with a 15 min interval: smokers were tested before and after smoking whereas non-smokers rested during the interval. Dependent behavioral variables included those of performance (speed and accuracy) and confidence (low rate of non-responding). The verbal task yielded an expected female advantage, and smoking had the gender-specific effect of increasing both speed and accuracy more clearly in males. In addition, smoking decreased the rate of non-responding (increase confidence) in women, thereby affecting preferred strategies for problem solving by shifting the female pattern towards the male pattern. The spatial task, which probably involved a more perceptual, rather than cognitive, level of functioning, produced no clear effects of smoking and gender, and yielded some laterality effects. The acute within-subject smoking manipulation wherein, among smokers, the first test was preceded by 10+ h of deprivation, whereas the second repeated task was preceded by the smoking of a cigarette (i.e. deprivation followed by partial release) did not affect the behavioral measures. In conclusion, smoking had a gender-specific effect on cognitive function: it improved the performance of males in a verbal task and increased the subjective confidence of females thereby affecting the preferred cognitive strategies for problem solving.

Adult↗

PubMed1994

Spatial scale shifts in peripheral vernier acuity.

Abutting line vernier acuity thresholds are markedly degraded in peripheral vision, while line detection thresholds are elevated to a much lesser extent. To study the spatial and orientation tuning properties of the mechanisms underlying peripheral line vernier acuity, abutting vernier thresholds were measured in the presence of one-dimensional band-limited spatial noise masks varying in orientation and spatial frequency. To examine the effects of these masks on target visibility, line detection thresholds were also measured. We find that in both the fovea and the periphery, noise masking produces marked elevations of vernier thresholds, which are tuned to both spatial frequency and orientation. (i) Spatial frequency tuning: in the fovea, the spatial frequency tuning is bandpass, with a bandwidth of approximately 2.5 octaves, and a peak spatial frequency of about 10 c/deg. In the periphery the spatial tuning is similar in bandwidth, however the peak shifts systematically to lower spatial frequencies with increasing eccentricity, implying that thresholds are mediated by spatial mechanisms tuned to progressively larger spatial scales with eccentricity. (ii) Orientation tuning: at all eccentricities there is a bimodal orientation tuning function for vernier acuity, consistent with the hypothesis that the responses of at least two filters, whose orientations straddle the target lines, are combined to extract vernier offset information. In contrast, at all eccentricities, line detection is most strongly masked when the mask and line target have the same orientation. For both the line detection and line vernier tasks, the scale of the most sensitive spatial mechanisms shifts systematically with eccentricity. The change in line detection threshold with eccentricity is approximately proportional to the variation in spatial scale; however this shift in spatial scale is not sufficient to account for the degraded peripheral vernier acuity. The extra increase in peripheral vernier thresholds may be a consequence of a high degree of positional uncertainty which adds noise at a stage following the combination of filter responses.

Contrast Sensitivity↗

PubMed1979

Information processing in the cerebral hemispheres: selective hemispheric activation and capacity limitations.

Several previous experiments have found that concurrently maintaining verbal information in memory influences visual laterality patterns (e.g., Hellige & Cox, 1976; Kinsbourne, 1975). The present article critically reviews existing experiments and reports five additional experiments designed to identify the mechanisms responsible for such effects. Experiment 1 demonstrates that laterality patterns are not influenced by a concurrent memory task that does not require verbal processing. (The verbal nature of the concurrent task was an important aspect of previous experiments.) Experiments 2 and 3 were designed to determined whether concurrent verbal memory primarily influences very early visuospatial processes or later processes such as those involved in visuospatial memory. In Experiment 2, observers indicated whether two simulteneously presented nonsense forms had the same shape. Observers held 0, 2, 4, or 6 words in memory during each shape judgment trial. Responses were faster when the forms were presented to the left visual field--right hemisphere (LVF-RH) than to the right visual field--left hemisphere (RVF-LH). This effect did not interact with memory set size. In Experiment 3, observers indicated whether either of two simultaneously presented forms was identical to a target form held in memory. Observers held 0, 2, or 6 words in memory on each trial. On same-as-target trials, responses were faster on LVF-RH trials than on RVF-LH trials in the no-word memory condition; this difference was reversed in the two-word and six-word conditions. The combined results of Experiments 2 and 3 suggest that concurrent verbal memory influences stages of processing beyond the initial registration of visuospatial information. Experiments 4 and 5 examined the influence of concurrent verbal memory on verbal laterality tasks. Observers indicated whether two simultaneously presented letters of different cases had the same name. In Experiment 4, different groups of observers held 0, 2, 4, or 6 words in memory on each letter-pair trial. In Experiment 5, memory set size was manipulated within subjects. On the same-pair trials of Experiment 4 and the first session of Experiment 5, responses in the no-memory condition were faster on RVF-LH trials than on LVF-RH trials; this difference was reversed in all of the work memory conditions. This shift is opposite to that found when the laterality task does not require verbal processing and further indicates that concurrent verbal memory influences processing stages beyond those that are common to the form-pair and letter-pair tasks. Neither directness-of-pathway nor attention-gradient laterality models can explain the entire pattern of results from the present experiments. Rather, the results suggest that the left hemisphere functions as a typical limited-capacity information processing system that can be influenced somewhat separately from the right hemisphere system.

Cerebral Cortex↗

PubMed2005

Adults with dyslexia demonstrate space-based and object-based covert attention deficits: shifting attention to the periphery and shifting attention between objects in the left visual field.

Performance on a covert visual attention task is compared between a group of adults with developmental dyslexia (specifically phonological difficulties) and a group of age and IQ matched controls. The group with dyslexia were generally slower to detect validly-cued targets. Costs of shifting attention toward the periphery when the target was invalidly cued were significantly higher for the group with dyslexia, while costs associated with shifts toward the fovea tended to be lower. Higher costs were also shown by the group with dyslexia for up-down shifts of attention in the periphery. A visual field processing difference was found, in that the group with dyslexia showed higher costs associated with shifting attention between objects in they LVF. These findings indicate that these adults with dyslexia have difficulty in both the space-based and the object-based components of covert visual attention, and more specifically to stimuli located in the periphery.

Adult↗

PubMed1997

A task-based approach to assessing lead exposure among iron workers engaged in bridge rehabilitation.

The assessment of worker exposures to airborne contaminants in the dynamic environment present at most construction sites poses considerable challenges to the industrial hygienist. In this study, we applied a task-based approach to the assessment of lead exposure among structural steel iron workers engaged in a large, complex bridge rehabilitation project. We evaluated the usefulness of task-based exposure data for the development of worker protection programs. Task-specific and multitask samples were collected, and operation-specific and 8-hr time-weighted averages were calculated. The task-specific data showed significant differences in exposure levels among different tasks. Arithmetic mean exposures varied from 1,357 micrograms/m3 lead for torch cutting and 989 micrograms/m3 for scaling to 31 micrograms/m3 for reaming and 4 micrograms/m3 for drilling. Our task-specific data were compared with the task-based exposure levels presented by OSHA in its Lead Exposure in Construction-Interim Final Rule (29 CFR 1926). There was good general agreement between our results and OSHA's reported data. Task-based data were very useful in exposure assessment and much more precise than full-shift and operation-based measurements in guiding strategies for worker protection. These findings suggest that task-based data should routinely be collected in evaluating exposure to lead and perhaps other toxic substances in construction work.

Air Pollutants, Occupational↗

PubMed2004

Spatiotemporal brain dynamics during preparatory set shifting: MEG evidence.

Humans can flexibly alter a plan of action to adjust their behavior adaptively in changing environments. Functional neuroimaging has shown distinct patterns of activation across a frontoparietal network responsible for switching and updating such plans of action or 'task sets.' However, little is known about the temporal order of activations within prefrontal or across with posterior regions subserving set-shifting operations. Here, whole-head magnetoencephalography (MEG) was used to explore the spatiotemporal brain dynamics in a modified version of the Wisconsin card-sorting test (WCST). Our task was designed to examine preparation of set-shifting rather than set-acquisition operations time locked to context-informative cues. Three cortical regions showed a larger number of MEG activity sources in response to shift and relative to nonshift cues: (a) inferior frontal gyrus (IFG; BA 45, 47/12), (b) anterior cingulate cortex (ACC; BA 24, 32), and (c) supramarginal gyrus (SMG; BA 40). Importantly, the timing of MEG activation differed across these regions. The earliest shift-related MEG activations were detected at the IFG (100-300 ms postcue onset), followed by two further peaks at the ACC (200-300 and 400-500 ms) and the SMG (300-400 and 500-600 ms). Several other prefrontal and posterior cortical areas were similarly activated by both shift and nonshift preparatory cues. The resulting temporal pattern of interactions within prefrontal and across with posterior association cortices is coherent with current models of task switching and provides novel information about the temporal course of brain activations responsible for the executive control of attention.

Adult↗

PubMed1989

Impaired extra-dimensional shift performance in medicated and unmedicated Parkinson's disease: evidence for a specific attentional dysfunction.

Groups of patients with Parkinson's disease, either medicated, or unmedicated and early in the course, together with age- and IQ-matched control subjects were tested in two paradigms measuring different aspects of selective attention. The first set of tests compared visual discrimination learning following intra- and extra-dimensional shifts, using a "total change" design in which each shift was made in the presence of novel exemplars of the compound stimuli used as discriminanda. The second test consisted of a visual search task in which the number of alternatives was varied. The results of the first experiment showed a selective deficit in both groups of Parkinsonian subjects in their ability to perform an extra-dimensional shift. In the visual search task, the patients were less accurate, but responded with equivalent choice reaction times to those of controls. The results are discussed in terms of the nature of the attentional dysfunction that occurs in Parkinson's disease.

Aged↗

PubMed2004

Muscle modes during shifts of the center of pressure by standing persons: effect of instability and additional support.

Muscle synergies in postural tasks have recently been studied using the framework of the uncontrolled manifold (UCM) hypothesis. A set of three hypothetical control variables, named M-modes, derived from the activity of 11 postural muscles, were identified. It was shown that postural synergies composed of these three M-modes preserve a certain shift of the center of pressure (COP) when subjects perform postural tasks while standing on a stable surface. In the present study we investigated the effects of support surface instability and availability of a light touch or grasp of a stable external support on the M-modes and their co-variation. The study was performed in two sessions. In the first session subjects released a load behind the body under four conditions: standing on a stable surface with no support (ST), standing on an unstable surface with no support (UN), standing on an unstable surface with a light touch (UN,T) and standing on an unstable surface with grasp of a stable object (UN,G). In the second session subjects performed two tasks: an arm movement backward and voluntary sway forward (towards the toes) under three conditions--ST, UN and UN,T. Principal component analysis was used to identify M-modes from data in the first session, and a UCM analysis was performed to study M-mode synergies in postural stabilization from data in the second session. A 'menu' of five M-modes was found, which were named either reciprocal M-modes or co-contraction M-modes based on the agonist-antagonist relationship of muscles comprising each mode. For a given task, subjects chose any three of these five M-modes in a subject- and task-specific manner. The reciprocal and co-contraction M-modes occurred equally frequently whether subjects stood on a stable or unstable support surface or whether a light touch was available or not. However, the co-contraction M-modes predominated when grasp of an object was available. In this condition, when the arm could be used for stabilization, there were M-modes uniting hip and shoulder muscles. However, the identified M-mode synergies were not found to lead to a consistent shift in the COP in any of the stability conditions. Possible reasons for this finding are discussed.

Adult↗

PubMed2005

Reduction of asthenopia related to accommodative relaxation by means of far point stimuli.

PURPOSE: To conduct an experimental investigation of the effect of accommodative relaxation using far point shift stimuli for the reduction of asthenopia. METHODS: Twenty-two female students accommodated to a far point shift stimuli during a 2-min period immediately after a 15-min sustained task on a three-dimensional display. Before and after the trial, their accommodative step response and symptoms were assessed. The far point shift stimuli in the optical system, which were presented on a refractometer, were created by moving the target scenery images from far to near, lineally centred about the far point position of each eye. During 2 min of fixating on the far point shift stimuli, changes in refraction were recorded in the same eye. RESULTS: While looking at the far point shift stimuli, 10 of 22 subjects had changes in refraction that showed a hypermetropic shift, and the other 12 subjects had changes in refraction that showed a myopic shift. The time taken for the accommodative step response from far to near post-trial in the myopic shift group was markedly prolonged, and the accommodative lag at the far target in the optometer was significantly increased. In the myopic shift group, the symptoms of "eye fatigue", "eye pain", "eye heaviness", and "eye dryness" also increased after the trial. In the hyperopic shift group, however, only the symptom of "eye dryness" increased, with no reduction of accommodation function. CONCLUSIONS: We suggest that accommodative relaxation by accommodative far point shift stimuli is effective in the reduction of asthenopia.

Accommodation, Ocular↗

PubMed1988

Effect of a mental arithmetic task on dark focus of accommodation.

Three subjective techniques for measuring accommodation (polarized vernier optometer, laser optometer, and a hand optometer based on the vernier principle) were used to measure subjects' dark focus while they performed a short-term mental arithmetic task. Compared with the initial values measured without the arithmetic task, significant changes in dark focus occurred when the task was performed. The effects depended on the initial dark focus of the subjects: in far-dark-focus subjects, inward shifts were generally observed; in near-dark-focus subjects, the dark focus shifted in different directions when different measuring techniques were used. The individual changes in dark focus due to the mental task were reproducible when the mean dark focus of the group shifted inward and when the same technique for measuring accommodation was used. The results have implications for the interpretation of dark focus shifts that are found following prolonged visual work at close distances, e.g. at visual display terminals.

Accommodation, Ocular↗

PubMed1976

Influence of three short-chain peptides (alpha-MSH, MSH/ACTH 4-10, MIF-I on) dimensional attention.

Male, albino rats were treated with alpha-MSH, MSH/ACTH 4-10, MIF-I or a diluent control solution and then tested on a visual discrimination problem. Immediately after acquistion of the visual task the animals were tested with a spatial extradimensional shift problem. The animals treated with the MSH/ACTH 4-10 and MIF-I acquired the discrimination nonsignificantly faster than animals treated with alpha-MSH or a placebo. A subproblem analysis of the EDS behavior indicated that the peptides significantly improved performance probably by affecting attention.

Adrenocorticotropic Hormone↗

PubMed2005

Bifrontal transcranial direct current stimulation slows reaction time in a working memory task.

BACKGROUND: Weak transcortical direct current stimulation (tDCS) applied to the cortex can shift the membrane potential of superficial neurons thereby modulating cortical excitability and activity. Here we test the possibility of modifying ongoing activity associated with working memory by tDCS. The concept of working memory applies to a system that is capable of transiently storing and manipulating information, as an integral part of the human memory system. We applied anodal and cathodal transcranial direct current (tDCS) stimulation (260 microA) bilaterally at fronto-cortical electrode sites on the scalp over 15 min repeatedly (15 sec-on/15 sec-off) as well as sham-tDCS while subjects performed a modified Sternberg task. RESULTS: Reaction time linearly increased with increasing set size. The slope of this increase was closely comparable for real and sham stimulation indicating that our real stimulation did not effect time required for memory scanning. However, reaction time was slowed during both anodal and cathodal stimulation as compared to placebo (p < 0.05) indicating that real stimulation hampered neuronal processing related to response selection and preparation. CONCLUSION: Intermittent tDCS over lateral prefrontal cortex during a working memory task impairs central nervous processing related to response selection and preparation. We conclude that this decrease in performance by our protocol of intermittent stimulation results from an interference mainly with the temporal dynamics of cortical processing as indexed by event-related sustained and oscillatory EEG activity such as theta.

Adult↗

PubMed2002

Long-lasting amelioration of visuospatial neglect by prism adaptation.

It has been shown that unilateral left neglect can be significantly improved for a short time after a short period of adaptation to a prismatic shift of the visual field to the right. In neuropsychological studies, however, there is no evidence demonstrating long-lasting effects following treatment by prism adaptation (PA). The first aim of the present study was to find out whether the short-term amelioration found after prismatic adaptation could be converted into long-term therapeutic improvement. Secondly, we investigated whether the improvement of neglect in standard tests could be generalized to ecological visuospatial tests. Thirdly, the effects of prism adaptation on different spatial domains (far, near and personal space) were evaluated. Fourthly, the influence of PA on high-order visuospatial functions, such as spatial representation, and on a low-order factor, i.e. sensory--motor bias, was investigated. Finally, we investigated the possible correlation between neglect amelioration, the adaptation effect and the visuomotor after-effect, as assessed by a pointing task during and after PA. Seven patients with right hemisphere lesion and left visuospatial neglect were treated with prismatic lenses in twice-daily sessions over a period of 2 weeks. In each training session, patients were required to perform a pointing task wearing base-left wedge prisms inducing a shift of the visual field to the right by 10. The presence of visual neglect and the duration of the amelioration achieved were assessed before the treatment and 2 days, 1 week and 5 weeks after treatment by using a standardized battery that included a series of behavioural and ecological visuospatial tests. Six control, untreated patients, matched to the experimental group for gravity and duration of illness, were submitted to the same tests at the same intervals as the experimental patients. The results showed an improvement in the experimental patients' performance after PA, which was maintained during the 5-week period after treatment. The amelioration of neglect was found in standard as well as in behavioural tests and in all spatial domains. In contrast, control patients did not show any improvement in neglect. The amelioration of neglect occurred only in patients who showed the adaptation effect and the after-effect in the pointing task. Neglect amelioration did not occur in one patient who did not show the adaptation effect and had an unstable after-effect. In conclusion, these findings show that prism adaptation is a productive way of achieving long-lasting improvements in neglect treatment.

Adaptation, Physiological↗

PubMed1994

Hand-hemispace spatial compatibility, precueing, and stimulus-onset asynchrony.

The role of attention and the resolution of coding conflicts in hand-hemispace spatial-compatibility effects was examined in a precueing experiment in which visual and vibrotactile precues, with various stimulus-onset asynchronies (SOAs), were presented in blocked and random order. It was expected that precues at the shorter SOAs would fail to facilitate the shifting of attention, as they occur too close to the imperative stimulus to be informative. The task would therefore approximate one of choice reaction time (RT), resulting in a hand-hemispace spatial-compatibility effect. Conversely, the longer SOAs would provide the subject with sufficient time in which to shift attention fully, and would therefore result in a task more like that of simple reaction time (SRT). It was expected that the hand-hemispace spatial-compatibility effect would then be absent. As was expected, this effect was present at the shorter SOAs, and absent at the longer SOAs. In Experiments 2 and 3, provision of a visual precue further facilitated attentional deployment, as did blocking the presentation of various SOAs in Experiment 3. Vibrotactile and visual precues did not differ in their ability to direct attention, implying that these modalities orient attention and precue location in essentially similar ways. These findings are discussed within the context of the mechanisms though to underlie the time course of spatial compatibility and the dissipation of a fading trace of interfering spatial codes.

Adult↗

PubMedDate not supplied

[Classifications of mental disorders: from Bertillon to ICD-10, the century of international collaboration].

The first International Classification of Diseases (ICD) was approved during the Congress of the Statistical International Institute, in Chicago, in Paris, in 1893. It was based on a list of diseases prepared by Jacques Bertillon. Minor changes were introduced in this classification during decennial revisions made at international meetings and it remained in use until 1948, when the World Health Organization's Provisional Committee was charged with the task producing ICD-6. ICD-6 represented a major shift from the previous internal conceptualization, particularity in what concerns the Chapter V., dealing with mental disorders. From 1955 on Who produced with approximately a 10-year interval ICD-7, 8 and 9. Few modifications in relation to ICD-6 were introduced by these revisions, except for the introduction of a glossary of terms in the chapter on mental disorders. This glossary had a major impact towards the development of a common language in psychiatry. Based on epidemiological findings, and based also on an intensive and extensive international network of clinicians and investigators, ICD-10 was published in 1992. It represented a substantial improvement regarding the conceptualization of the classification of mental disorders, in relation to previous revisions of the ICD. Future tasks relating to ICD-10 include training of health personnel for its proper utilization, in addition to finalizing further ICD-10 versions, e.g. for research purposes and for primary health care use.

Animals↗

PubMed1983

Attenuation of reversal deficits of mice with septal lesions by shifts in the motivational context.

Response perseveration following septal lesions, demonstrated on tasks that require change of a learned pattern of responding, depends in part on a relatively constant motivational context. The present experiment examined the effects of concurrent changes in the temperature of the water in a water-escape maze and the reversal of a spatial discrimination in mice that had received either septal lesions or control surgery. Control and experimental mice were trained on a spatial discrimination in either 17 or 34 degrees C water. Following acquisition, reversal training was conducted in the maze filled with the same-temperature water used during acquisition or water temperature as well as spatial reinforcement contingencies were reversed. When the water temperature remained constant across acquisition and reversal, the mice with septal lesions showed persistence during reversal training. Changing the water temperature concurrently with the institution of reversal training attenuated the perseverative deficits of mice with lesions, in contrast to the relative lack of effect in control animals. These results are discussed within the framework of the role that the septal region plays in attention.

Animals↗