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PubMed1984

Voluntary control of two lateralized conscious states: validation by electrical and behavioral studies.

A subject is described who can voluntarily select and hold either of two qualitatively different states of consciousness. Evidence is presented which confirmed differential left or right hemisphere dominance in each state. Asymmetries of EEG alpha and task performance scores indicated a state-dependent shift in functional lateralization. Evoked response studies showed directional changes in rate of interhemispheric transmission correlated with state-related hemisphere dominance. These findings demonstrated that capability for voluntary endogenous control of cerebral dominance under natural conditions.

Adult↗

PubMed1993

Spatial learning during the course of autoimmune disease in MRL mice.

The present study examines whether autoimmune MRL-lpr mice develop impairments in learning and memory that correlate with changing severity of lupus-like disease. MRL-lpr mice (n = 20) were tested in the Morris water-maze at 12, 14, 16 and 18 weeks of age. Age-matched controls were congenic MRL +/+ mice (n = 20) that develop the disease much later. Immune status was assessed by the presence of anti-nuclear antibodies (ANA), brain-reactive antibodies, proteinuria, and haematocrit. Learning rates and memory retention did not differ between the substrains, and did not correlate or deteriorate with advancing age and autoimmunity. However, the baseline performance level in autoimmune MRL-lpr mice was shifted, as evidenced by a consistently longer task-solving latencies. Thigmotaxic swimming (along the pool wall) was pronounced in the MRL-lpr group, and was associated with the observed difference in performance. The present study does not support the notion that learning/memory abilities of autoimmune MRL-lpr mice are impaired per se, but may support the hypothesis that the rapid progress of humoral autoimmunity affects the emotionality of lupus-prone mice.

Animals↗

PubMed1995

Postprocessing of functional MRI data of motor cortex stimulation measured with a standard 1.5 T imager.

Functional magnetic resonance imaging (fMRI) is usually based on acquisition of alternating series of images under rest and an activation task (stimulus). Brain activation maps can be generated from fMRI data sets by applying several mathematical methods. Two methods of image postprocessing have been compared: (i) simple difference of mean values between rest and stimulation, and (ii) Student's t-test. The comparison shows that the difference method is very sensitive to arbitrary signal fluctuations as seen mainly in large vessels (e.g., in the sagittal sinus), leading to insignificantly activated spots in brain activation maps. In contrary, Student's t-test maps show strongly reduced sensitivity for fluctuations and have the advantage of giving activation thresholds by setting significance levels. This allows the comparison of activation strength between patient collectives by using a grid overlay technique leading to an observer independent quantification of the stimulation effects. The method was able to reproduce previous findings of activation differences between healthy volunteers and schizophrenic patients. Moreover, a simple algorithm for the correction of slight head movements during the functional imaging task is presented. The algorithm is based on shifting the fMRI data set relative to a reference image by maximizing the linear correlation coefficients. This leads to a further reduction of insignificant brain activation and to an improvement in brain activation map quality.

Adult↗

PubMed2005

Sustained neural activity associated with cognitive control during temporally extended decision making.

Decision making has both cognitive and affective components, but previous neuroimaging studies in this domain predominantly have focused on affect and reward. The current study examined a decision-making paradigm that placed strong demands on cognitive control processes by making reward payoffs contingent upon decision-making history. Payoffs were maximized by choosing the option that, paradoxically, was associated with a lower payoff on the immediate trial. Temporal integration requirements were manipulated by varying, across conditions, the window of previous trials over which the reward function was calculated. The cognitive demands of the task were hypothesized to engage neural systems responsible for integrating and actively maintaining actions and outcomes over time and the top-down biasing of response selection. Brain activation was monitored with functional magnetic resonance imaging (fMRI) using a mixed-blocked and event-related design to extract both transient and sustained neural responses. A network of brain regions commonly associated with cognitive control functions, including bilateral prefrontal cortex (PFC), bilateral parietal cortex, and medial frontal cortex, showed selectively sustained activation during the task. Increasing temporal integration demands led to a shift from transient to sustained activity in additional regions, including right hemisphere dorsolateral and frontopolar PFC. These results demonstrate the contribution of cognitive control mechanisms to temporally extended decision-making paradigms and highlight the benefits of decomposing activation responses into sustained and transient components.

Adult↗

PubMed2004

Dopamine in the orbitofrontal cortex regulates operant responding under a progressive ratio of reinforcement in rats.

Prefrontocortical dopamine (DA) plays an essential role in the regulation of cognitive functions and behavior. The orbitofrontal cortex (OFC) receives a dopaminergic projection from the ventral tegmental area and is particularly important for goal-directed appetitive behaviors and for the neural representation of reward value. We here examined the effects of DA receptor blockers locally infused into the OFC, on instrumental behavior under a progressive schedule of reinforcement. After continuous reinforcement training (lever pressing for casein pellets) rats received bilateral intra-OFC-infusions of the DA D1-receptor antagonist SCH23390 (3 microg/0.5 microl), the DA D2-receptor antagonist sulpiride (3 microg/0.5 microl), or phosphate buffered saline through chronically indwelling cannulae. Immediately after infusion they were tested under a time-constrained progressive ratio schedule of reinforcement (3, 6, 9, 12, ... lever presses for 1 casein pellet within 180 s). Both SCH23390 and sulpiride led to a significant reduction of the break point (cessation to respond to the increasing criterion of instrumental effort) compared to vehicle infusions. A food preference test revealed no drug effects on the amount of consumed pellets and on the preference of casein pellets over laboratory chow. Leftward shifts of the break point in progressive ratio tasks indicate a disturbance of the mechanisms that translate motivation into appetitive behavior under conditions of increasing instrumental effort. Therefore, our data indicate that orbitofrontal dopamine is necessary for reward-related instrumental behavior.

Analysis of Variance↗

PubMed2006

Task-induced deactivations during successful paired associates learning: an effect of age but not Alzheimer's disease.

Task-induced fMRI deactivations during successful encoding and retrieval of visuospatial paired associates were examined at different levels of task difficulty in younger and older adults (Experiment 1), and older adults with and without mild probable Alzheimer's disease (AD) (Experiment 2). Irrespective of the level of task difficulty, common deactivations (determined through the use of conjunction analyses) were observed in the lateral and medial prefrontal, anterior and posterior cingulate, and temporal brain regions and in the claustrum during both encoding and retrieval in younger and older adults (Experiment 1). In AD patients and healthy older adults, common deactivations were found in posterior cingulate, temporal, and lateral parietal regions and in the insula and claustrum during encoding and retrieval of paired associates (Experiment 2). As task difficulty increased, irrespective of the type of task, the magnitude of task-induced deactivations increased in the medial prefrontal/superior frontal gyrus and middle/posterior cingulate cortex in younger and older adults (Experiment 1), and in the middle cingulate cortex in older adults with and without AD (Experiment 2). In Experiment 1, greater deactivation was observed in the anterior cingulate gyrus in older compared to younger adults during retrieval of paired associates which was attributed to greater suppression of task-unrelated thoughts in the older group. No significant differences in task-induced deactivation, or in the type of relationship exhibited between deactivation and task difficulty, were observed between older adults with and without AD (Experiment 2). It was suggested that this was related to the matching of successful task performance and task difficulty across patient and control groups. Following previous proposals, task-induced deactivations were suggested to underlie a shifting of attentional focus from monitoring of the self and the environment (through attenuation of these activities) to external, goal-directed behaviour.

Adult↗

PubMed1990

Left handedness and handedness switch amongst the Chinese.

The incidence of left handedness amongst the Chinese, as in the case of people with more traditional cultures, is reported to be low. However, there is a group of native left handers, often unrecognized as such, who use the right hand for writing and drawing but the left hand for most other tasks. They had experienced pressure during childhood to shift their preferred hand from left to right. This paper compares the handedness profile, eyedness, footedness, and finger tapping performance of right handed, left handed, and handedness switch Chinese subjects.

Adult↗

PubMed2003

Agency-nursing work: perceptions and experiences of agency nurses.

This paper explores agency-nursing work from the perspective of agency nurses to gain in-depth understanding of their clinical practice, their relationships with the employing agency, hospitals and permanent nurses, and their professional status. For this study, individual interviews were conducted with ten agency nurses who were registered with one of three nursing agencies in Melbourne, Australia. Five major themes emerged from interview data: orientation, allocation of agency nurses, reasons for doing agency-nursing work, experiences with hospital staff, and professionalism. The findings reveal that the primary reason for nurses engaging in agency-nursing work is for the flexibility it offers. While agency nurses described a commitment to professionalism, the findings emphasise the need to establish effective communication networks between agency nurses, nursing agencies and hospital institutions. Such communication between stakeholders is important to facilitate discussion of issues such as appropriate notification of shift availability, appropriate assignment of work and recognition of the agency nurse as a valuable member of the health care team. In particular, the findings highlight the importance of comprehensive orientation and education for agency nurses to shift the focus of their daily work from task completion to more comprehensive patient care.

Adult↗

PubMed2002

Event-related potential measures of the inhibition of information processing: II. The sleep onset period.

The loss of consciousness during the sleep onset period is associated with dramatic changes in information processing. Human event-related potentials (ERPs) reflect these changes. Short- and mid-latency ERPs are only minimally affected by sleep onset. On the other hand, long-latency ERPs are very much affected. A negative wave, N1, peaking at approximately 100 ms gradually decreases in amplitude until it reaches baseline level during definitive stage 2 sleep. The changes in N1 are especially apparent when the subject no longer signals awareness of the external stimulus or when stage 1 is dominated by theta activity in the EEG. The positive peaks, P1 and P2, peaking at approximately 50 and 180 ms, respectively, may appear to increase in amplitude (i.e. also be less negative). A long-lasting processing negativity (PN) may overlap and summate with these peaks during the waking state. During sleep onset, the PN dissipates, thus explaining the apparent positive baseline shift in the ERP waveform. In an oddball task, when an alert and awake subject detects a rare, relevant stimulus, a large positive wave, P300, maximum over parietal areas of the scalp, is observed. This P300 is, however, widely dispersed and can be observed over frontal areas of the scalp. When the subject no longer signals detection of this target stimulus, P300 can no longer be recorded. During stage 1, the parietal P300 remains large, providing the subject overtly detects the target. The amplitude of the frontal aspect of P300 is much reduced as response times slow. This may reflect deactivation of the frontal lobes during the sleep onset period. The infrequent change of an otherwise rapidly presented homogenous train of stimuli is associated with another long-lasting negativity, the mismatch negativity (MMN). The MMN also decreases in amplitude during the sleep onset period, reaching baseline level during definitive sleep. The vertex sharp wave (VSW) becomes apparent during the sleep onset period. Associated with the VSW is a late negative ERP, sometimes called the sleep N2 or the N350, peaking between 300 and 350 ms. It is unique to the sleep onset and sleep periods, becoming very large during stage 1-theta or when the subject no longer shows signs of awareness of the external stimulus.

Animals↗

PubMed1999

Laterality changes accompanying symptom remission in schizophrenia following treatment with eicosapentaenoic acid.

INTRODUCTION: A patient with severe intractable symptoms of schizophrenia was treated for 6 months with a fatty acid supplement, primarily as a test of the hypothesis that membrane phospholipid metabolism is abnormal in schizophrenia. His symptomatology was predominantly positive, consistent with an 'Active' syndrome thought to reflect a relative imbalance of left over right hemispheric activation. Longitudinal studies have previously shown changes in functional lateralisation with symptom remission in schizophrenia, hence this was examined at intervals over the 6-month period. METHOD: The subject was a 30-year-old male with DSM-IV schizophrenia. For 2 years prior to this study his clinical profile had not changed and he had remained free of neuroleptic medication. Treatment with 30 ml/day of emulsion rich in eicosapentaenoic acid was started, and clinical ratings were made at monthly intervals for 6 months. Motor laterality had been assessed using Annett's handedness scale and pegboard task 1 year pre-baseline, and this was repeated at 0, 3 and 6 months from the start of treatment. RESULTS: As measured by the Schedules for the Assessment of Positive Symptoms and Negative Symptoms, a marked reduction in his symptoms was first apparent at 2-month follow-up; further improvement followed, so that at the 6-month point few symptoms remained. Corresponding to his clinical improvement, the patient's performance on the pegboard task at 3-month follow-up had shifted from a strong right-hand advantage to near symmetry, owing to a marked improvement in his left-hand scores. On retest at 6 months this change in asymmetry was also maintained. CONCLUSIONS: These findings suggest that treatment with certain fatty acids may have significant benefits in the management of schizophrenia. They are also consistent with existing evidence that an Active syndrome of schizophrenia reflects a left over right hemispheric imbalance which is functional in nature, and can therefore change with symptom remission.

Adult↗

PubMed2000

Is attentional focusing an inhibitory process at distractor location?

This study investigated whether attentional focusing is an inhibitory mechanism of lateral distractor stimuli. Attentional focusing is defined as the visual system capacity to vary the spatial extent of the attended area without shifting attention. A two-choice-reaction time task with compatible and incompatible flankers was used. Results were interpreted on the basis of the time course of attentional focusing.

Adult↗

PubMed2004

Effects of additional tasks on language perception: an event-related brain potential investigation.

The authors investigated effects of task and overlapping processing load on semantic processing. In 3 experiments the brain potential component N400 was elicited by synonymous and nonsynonymous spoken noun pairs that were to be classified according to semantic relatedness. The time course of the N400 component to the nouns was delayed, and its amplitude was reduced when additional tasks had to be performed. The delay increased with temporal overlap and was more pronounced for language-related than for spatial additional tasks. Delays of N400 were also caused by a compatibility manipulation in the additional tasks. Theoretical accounts of the observed interference of overlapping tasks with language perception in terms of attentional shifts were discarded. Explanations in terms of resource sharing and single channel processing are discussed.

Adult↗

PubMed1992

Kinematic adaptations to perturbations as a function of practice in rhythmic drawing movements.

Kinematic adaptations in multijoint rhythmic drawing movements were investigated under unexpected perturbations in friction levels between stylus and writing surface. Changes in coupling and stability properties were assessed as a function of practice level by applying perturbations to subjects' dominant and nondominant limbs. Under nonperturbation and perturbation conditions, joint motions of right-handed subjects were highly coupled in the nondominant limb and uncoupled in the dominant limb. Stability analyses of the kinematic responses in the phase plane showed a relatively higher intrajoint resistance to perturbations in the nondominant limb as compared to the dominant limb for the elbow joint. indicating a decrease in global joint stiffness with practice. These changes in joint coupling and stiffness with practice were not observed for left-handed subjects. In addition, the stability to perturbations in the end-effector (stylus) kinematics was related to the amount of joint coupling in the nondominant limb, whereas in the dominant limb there existed no such coupling. It was concluded that (a) practice changes the responses to perturbations from anatomically specific early in practice to task-specific late in practice, and (b) this shift is related to the stability in the joint phase-plane dynamics, degree of coupling between joint angles, and the decoupling of the dynamics in the intrinsic and extrinsic control spaces.

Journal Article↗

PubMed2004

Recollection deficits in dysphoric mood: an effect of schematic models and executive mode?

Depression and dysphoric mood states are often accompanied by quantitative or qualitative shifts in performance across a range of retention tasks. This study focuses on the recollection of both autobiographical events and word lists in dysphoric states. Recollection occurs when people are aware of some contextual detail allied to the encoding experience. This study establishes the presence of a recollection deficit in dysphoria in two distinct paradigms. In both autobiographical recall and in recognition memory, recollection in a dysphoric group was at lower levels than recollection in matched controls. The study examines the hypothesis that the extent of recollection is influenced by two factors: (1) the degree of differentiation of schematic mental models; and (2) the executive mode that predominates when memory tasks are carried out, with the latter assumed to be altered by rumination. The relationship between responses based on recollection and alternative mnemonic responses could be predicted by measures of these two factors. The results are discussed in terms of the Interacting Cognitive Subsystems model (Teasdale & Barnard, 1993) and the perspective it offers on the relationship between meaning systems and executive functions (Barnard, 1999).

Adult↗

PubMed2001

Biological monitoring of n-hexane exposure in Portuguese shoe manufacturing workers.

Occupational risk of exposure to organic solvents concerned many shoe manufacturing workers. The most common organic solvents found in workplace environments were n-hexane and others hexane isomers. The aim of this study was to evaluate the exposure of shoe manufacturing workers to n-hexane, with 2,5 hexanedione in urine (2,5HD) as a biomarker and to investigate effect in 2,5 HD excretion of the co-exposure to other organic solvents. Post-shift urine samples from workers who performed gluing tasks (n = 45) in five shoe manufacturers were collected, as well as urine samples from a similar number of unexposed controls (n = 51) in the same factories. 2,5 HD was measured by capillary gas chromatography. Air monitoring of organic solvents in the workplaces was performed and the compounds were analyzed by gas chromatography. Significant more 2,5 HD was found in the urine of personnel who performed gluing tasks than in the unexposed workers. A significant correlation was observed between n-hexane exposure and urinary 2,5 HD, with a high correlation coefficient. Multiple regression analysis indicated that n-hexane exposure and co-exposure to others solvents were significant predictors of the concentration of 2,5 HD. Co-exposure led to higher urinary 2,5 HD concentrations. The significant effect of co-exposure reinforces the interest of biological monitoring for n-hexane exposure evaluation. In case of multiple exposures, biological monitoring can be a better predictive measurement for early detection of n-hexane neurotoxic lesions than air monitoring data.

Adhesives↗

PubMed1991

Stability and change in the informal task support network of frail older persons.

This study examines predictors of stability and change in composition, size, and intensity of help of the informal task support networks of frail elders and their primary caregivers. The sources of data are the 1982 and 1984 National Long Term Care Surveys and the companion 1982 Informal Caregivers Survey. There was slightly more stability than change in the size and composition of family task support networks. We found little evidence that shifts in network composition were in the direction of including more distant kin. Changes in network size and intensity of help occurred in response to changes in health and functional status of the frail older person, but not in response to the level of burden of the primary caregiver.

Adolescent↗

PubMed2005

Neuropsychological deficits in adolescents with conduct disorder and comorbid bipolar disorder: a pilot study.

OBJECTIVE: We report pilot data on neuropsychological deficits in aggressive juvenile offenders with and without bipolar disorder compared with each other and healthy controls. METHOD: We assessed 52 adolescents and their parent or guardians: 36 incarcerated juvenile offenders and 16 community controls using the Schedule for Affective Disorders and Schizophrenia for School Age Children, Present and Life-Time Version and a neuropsychological testing battery. All incarcerated subjects (n=34) met criteria for Conduct Disorder (CD); 26 are classified as Non-BD-CD, and eight with CD and Bipolar disorder (CD-BD). These subjects were compared to community controls (n=16) matched for age, gender, SES and ethnicity. RESULTS: Relative to controls, the Non-BD-CD subjects' impairments (p<0.05) were in cognitive ability, set shifting/inhibition, planning and verbal memory-language functioning. The CD-BD group displayed impairments (p<0.05) relative to controls in cognitive ability, set shifting, verbal memory-language functioning, and visuospatial tasks. The Non-BD-CD and CD-BD groups however did not display significant differences on most neuropsychological measures compared with each other. When we controlled for Attention Deficit Hyperactivity Disorder, the Non-CD-BP subjects continued to show deficits on Verbal measures where the CD-BD subjects maintained deficits in measures of cognitive ability, verbal measures and visual spatial tests. CONCLUSIONS: Juvenile offender with CD displayed a wide range of deficits on neuropsychological testing compared with controls. Although juvenile offenders with and without BD differed on their clinical presentation, differences on neuropsychological measures are not specific and may be related to comorbid diagnoses.

Adolescent↗

PubMed1993

The effects of between-source discriminability on attended and unattended auditory ERPs.

Event-related potentials (ERPs) for tone pips from attended and unattended sources, which varied on discriminability, were compared with ERPs for the same stimuli recorded during performance of a visual task. This comparison revealed that Nd, the negative shift of attended relative to unattended ERPs, consisted of three components: a negativity in the attended ERP from 100 to 270 ms, a positivity in the unattended ERP from 170 ms to the end of the epoch, and a second negativity in the attended ERP from 270 to 700 ms. In general, the later onset of early Nd with more difficult between-source discriminations could be attributed to the later onset of the positivity in unattended ERPs. A number of hypotheses were advanced for the origin of the unattended positivity: the suppression of the later of two negative components in the 100-220-ms range, an enhanced P2 component, an endogenous positivity, or the resolution of a protracted negativity elicited by preceding attended stimuli.

Adolescent↗