Neuropsychological function in young patients with unipolar major depression

BACKGROUND

While neuropsychological studies have consistently reported impaired cognition in elderly patients with unipolar depression, studies of cognitive function in younger patients with depression have produced equivocal results. The aim of this study was to examine the presence and nature of cognitive deficits in young patients with depression.

METHODS

Neuropsychological function was assessed in 20 young patients with unipolar depression, in comparison to 20 age-, education- and IQ- matched controls. Subtests from the Cambridge Neuropsychological Test Automated Battery (CANTAB) were employed, as this battery has proved sensitive to deficits in middle-aged and elderly patients with depression.

RESULTS

The patients were not impaired for short-term memory capacity, spatial working memory, planning ability, cognitive speed, delayed matching to sample or recognition memory. Compared to controls, the patients showed impaired subsequent movement latencies on the Tower of London task, suggesting deficits in the ability to sustain motor responses in depression. The depression group were also impaired on the task of attentional set shifting, requiring more trials to criterion at the intradimensional stage of the task and being more likely to fail the task at the extradimensional shift stage than controls. Further analysis indicated that half of the depression group failed to complete all stages of the set shifting task. These patients were more likely to have required in-patient hospitalization at some time during their illness.

CONCLUSIONS

These results indicate that there are specific cognitive deficits in young patients with depression and that their presence may be related to a history of hospitalization.

Object-based visual attention in luminance increment detection?

A cued reaction time task was used to test the hypothesis that there is an 'object-based' component to shifts of attention mediating the detection of luminance increment targets. The test stimulus consisted of two intersecting triangles forming a 'Star of David'. In two experiments, the cue was a brief brightening of one triangle. The target (a bright green dot) appeared on one of the triangles after a delay of 100, 200 or 500 msec. In one experiment, the target was more likely to appear on the cued triangle. In a second experiment, there was no contingency between cue and target. In both cases, reaction times to targets which appeared outside (but not inside) the cued triangle were more than 10 msec longer than other targets, but only at the shorter cue-target delays. This indicates that the attentional system which regulates luminance increment detection cannot select the cued triangle. It appears that the attentional spotlight can be briefly deformed into a triangular shape, and that it is the rapid, fast-decaying and reflexive exogenous system, rather than the slower acting, persistent and voluntary endogenous system, that mediates this effect. A third experiment using a central, symbolic cue showed no significant cue-validity effects, indicating no contribution from the endogenous system. It is concluded that tasks requiring only stimulus detection cannot unequivocally discriminate between spatial and object-based components of attention.

Manipulating the disengage operation of covert visual spatial attention

Processes of covert visual spatial attention have been closely linked to the programming of saccadic eye movements. In particular, it has been hypothesized that the reduction in saccadic latency that occurs in the gap paradigm is due to the prior disengagement of covert visual spatial attention. This explanation has received considerable criticism. No study as yet as attempted to demonstrate a facilitation of the disengagement of attention from a covertly attended object. If such facilitation were possible, it would support the hypothesis that the predisengagement of covert attention is necessary for the generation of express saccades. In two experiments using covert orienting of visual attention tasks (COVAT), with a high probability that targets would appear contralateral to the cued location, we attempted to facilitate the disengagement of covert attention by extinguishing peripheral cues prior to the appearance of targets. We hypothesized that the gap between cue offset and target onset would facilitate disengagement of attention from a covertly attended object. For both experiments, responses to targets appearing after a gap were slower than were responses in the no-gap condition. These results suggest that the prior offset of a covertly attended object does not facilitate the disengagement of attention.

Collection and normal levels of the amyloid precursor protein in plasma

The amyloid precursor protein is contained in platelet alpha granules and released with degranulation. Methods are described to control for amyloid precursor protein release from platelets during blood collection and processing. In normal subjects (n = 97; age range, 44-84 years), the average plasma level of amyloid precursor protein was 6.5 +/- 1.8 ng/ml.

Deficits in the endogenous redirection of covert visual attention in chronic schizophrenia

In patients with schizophrenia, abnormal performance on the antisaccade task suggests that for overt attentional shifts, there is difficulty with the endogenous modes have opposite goals. We examined whether patients with schizophrenia also have difficulty with the endogenous control of exogenous orienting when endogenous and exogenous control of exogenous orienting for covert shifts of attention. Fifteen medicated patients with chronic schizophrenia and 15 matched controls performed two versions of the covert orienting of attention task (COVAT). On one COVAT, targets appeared at the cued location (TAC) on all trials. On the second COVAT, targets appeared at the contralateral location to the cue (TCC) on all trials. Reaction time (RT) for TAC and TCC trials was equal in the control group. However, for the schizophrenia group, RT for TCC trials was significantly slower than RT for TAC trials. This indicates that patients with schizophrenia were unable to inhibit the orienting of attention to peripheral cues even when they knew that targets would never appear at the same location as the cue. These results suggest that patients with chronic schizophrenia have difficulty utilizing the endogenous strategies to inhibit exogenous covert attentional shifts.

Cognitive deficits in Machado-Joseph disease

Cognitive function was examined in 6 patients with genetically confirmed Machado-Joseph disease (MJD) and 15 age- and ethnically matched controls using a series of subtests from the Cambridge Neuropsychological Test Automated Battery (CANTAB), a touch screen-based testing system previously validated in a number of movement and neurodegenerative disorders. The MJD patients had deficits in visual attentional function that were characterized by a slowing of the processing of visual information when task demands were high and an inability to shift attention to previously irrelevant stimulus dimensions to discriminate between complex stimuli. Tests of learning and visual memory were normal. These results demonstrate that specific cognitive deficits occur in patients with MJD, independent of motor dysfunction, and these deficits may reflect disruption to frontosubcortical pathways.

Asymmetries in the covert orienting of visual spatial attention to spatial and non-spatial cues in Alzheimer's disease

The ability to direct covert visual spatial attention to the left (LVF) and right visual field (RVF) was examined in 15 patients with mild to moderate Alzheimer's disease and 15 age- and education-matched controls using the covert orienting of visual spatial attention task (COVAT) modified to include both spatial and non-spatial cues. Subjects responded with a button press when they detected a target at a location 8 degrees to either the left or right of fixation. On 70% of trials a spatial cue was flashed at the target location before the target appeared. On 15% of trials the spatial cue was flashed at the location contralateral to where it would appear and on the remaining 15% of trials non-spatial diffuse cue preceded targets. The cue to target interval (CTI) varied between 150 and 550 ms. Mean reaction times for each cuetype in the RVF and LVF were calculated. Compared with controls, the percentage of trials excluded because of very slow reaction times was significantly greater in the Alzheimer's disease group for the 550 ms CTI. Analysis of the symmetry of reaction times to LVF and RVF targets for the 150 ms CTI enabled us to classify Alzheimer's disease subjects into three subgroups based on the hemifield of abnormally slow attentional biases. The first subgroup showed a significant slowing of reaction time to all LVF targets, the second showed a significant slowing of reaction time to all RVF targets and the third showed a significant slowing of reaction time to both LVF and RVF targets. Patients with Alzheimer's disease who showed an abnormal attentional bias performed significantly better on neuropsychological tests of memory, language and executive function than Alzheimer's disease patients with no attentional bias. Eight of the Alzheimer's disease subjects were assessed serially on at least six occasions over a 12-month period. The initial classification of abnormal attentional bias or no attentional bias was reliable for seven Alzheimer's disease subjects. One Alzheimer's disease subject, initially classified as having a slowed rightward attentional bias, in subsequent testing over the 12-month period was more consistent with symmetrical COVAT performance. Control subjects showed no attentional biases over the 12-month period and the magnitude of asymmetric attentional slowing over the 12-month period was significantly more variable in individual Alzheimer's disease subjects than in controls. The presence of subgroups of patients with Alzheimer's disease with qualitatively different COVAT performance indicates a large between-subject variability in attentional deficits in Alzheimer's disease. The presence of asymmetric attentional slowing and milder neuropsychological deficits in a subgroup of patients with Alzheimer's disease suggests that in these patients there is functional impairment of attentional areas in only one hemisphere rather than an asymmetric impairment of both hemispheres and that the neurodegenerative disease process may have been less advanced or in an earlier stage than that present in Alzheimer's disease patients with symmetric attentional performance and bilateral COVAT impairment. The preservation of asymmetric attentional slowing over time, together with the increased intra-subject variability in the magnitude of these asymmetries, suggests that asymmetrical COVAT performance represents a reliable reflection of underlying hemispheric function in Alzheimer's disease, although designation of asymmetrical attentional biases should be made on the basis of two or more sequential testing sessions.

Asymmetries in the covert orienting of visual spatial attention in schizophrenia

The presence of attentional asymmetries in patients with schizophrenia was investigated with particular emphasis on the effects of stage of disease, medication status and clinical symptom severity. A modified version of Posner's covert orienting of visual attention task (COVAT) which included both spatial and non-spatial cues was administered to six volunteer samples of subjects which consisted of (i) 15 unmedicated and acutely psychotic male subjects with schizophrenia, (ii) 15 male subjects with schizophrenia who had been receiving medication for 14-21 days, (iii) 10 chronic male schizophrenic subjects who had been receiving medication for at least two years, (iv) 10 acutely psychotic male subjects with non-schizophrenic psychoses, (v) 15 subjects with unilateral brain frontal lobe (n = 6) or parietal lobe (n = 9) lesions, (vi) and 15 male control subjects. Measures of saccadic and pursuit eye movements were also obtained from unmedicated and recently medicated subjects with schizophrenia. COVAT attentional asymmetries were present in unmedicated subjects with schizophrenia for the 150 msec stimulus onset asynchrony (SOA). These asymmetries arose because reaction times (RTs) to right visual field targets were significantly slower than RTs to left visual field targets when targets followed invalid spatial or non-spatial cues. These asymmetries were qualitatively similar to those found in the patients with unilateral parietal lobe lesions. Attentional asymmetries partially resolved with brief periods of medication and completely resolved with long periods of medication. No asymmetries were found in controls nor in unmedicated subjects without schizophrenia. No asymmetries of ocular motor function were found. In schizophrenia, attentional asymmetries may reflect a deficit in the disengagement of visual attention from the right visual field and appear to be a stage marker for the disease. However this attentional deficit is dynamic and may reflect disruption to the neurocognitive network controlling attention at the level of the anterior cingulate cortex.

An attentional grasp reflex in patients with Alzheimer's disease

Motor and visual grasp reflexes often occur as part of the symptomatology of Alzheimer's disease (AD). Similar grasp reflexes may also be associated with the impaired performance of AD patients on tasks which require direction of visual attention without eye movements. The covert orienting of visual attention task (COVAT) requires subjects to keep their eyes fixed on a central point and manually respond to the appearance of a peripheral target in one of two locations in the left or right visual field. Before the target appears, a cue is presented at either the target location or the contralateral location to the target, although the nature of the cue is not known until the target appears. We hypothesised that the attentional grasp reflex would become evident in patients with AD when attentional shifts away from the cue were required but there was no target for the shift present. Twelve patients who met the clinical criteria for AD and 12 age and education matched controls were administered three COVAT conditions in which the target appeared at the cued location with either an 80, 50 or 20% probability. For the 80 and 50% probability conditions. RTs for targets at the cued location were significantly faster than RTs for targets contralateral to the cue in both AD subjects and controls indicating that AD subjects were able to disengage attention when there was a target for the attentional shift. For the 20% probability condition, control subjects showed significantly faster RTs for targets appearing contralateral to the cue than for targets at the cued location indicating that when they expected the target to appear in the opposite visual field to the cue, they could initiate the shift of attention before the target appeared. However, AD subjects continued to show significantly faster RTs for targets at the cued location than for targets appearing contralateral to the cue, despite the high probability that targets would not occur at the cued location. This suggests that the covert redirection of attention away from a peripheral visual cue could not be initiated until the contralateral target appeared. Taken together these results suggest an attentional grap reflex in patients with AD.

Abnormalities of visual spatial attention in HIV infection and the HIV-associated dementia complex

Covert orienting of visuospatial attention (COVAT) was examined in 88 homosexual or bisexual men: 12 with mild HIV-associated dementia complex (ADC), 30 neurologically intact with AIDS (NI-AIDS), 23 asymptomatic HIV+ (HIV+ASX), and 23 HIV-negative control subjects. In mild ADC, COVAT was normal for spatial but impaired for nonspatial cues; 17% of NI-AIDS and HIV+ASX subjects had similar COVAT impairment patterns and also showed cognitive deficits. HIV+ subjects with normal COVAT showed normal cognitive performance. Impairment of nonspatial attentional processing in the ADC subjects and subgroups of the neurologically intact HIV+ subjects may reflect early subcortical dysfunction caused by HIV infection. COVAT assessment may be sensitive for detection of early subclinical neurological impairment in HIV infection.

Neuropsychological characterization of the AIDS dementia complex and rationalization of a test battery

OBJECTIVE

To define the neuropsychological deficits present in mild human immunodeficiency virus type 1 (HIV-1) associated with the acquired immunodeficiency syndrome (AIDS) dementia complex (ADC) and to develop a rational neuropsychological test battery for its diagnosis.

DESIGN

Survey.

SETTING

Subjects were recruited from large metropolitan hospital outpatient clinics and were all living independently in the general community.

PATIENTS

Three volunteer samples of homosexual-bisexual men: (1) 15 patients who met clinical and research criteria for mild ADC; (2) 27 HIV-seronegative (HIV-) controls; and (3) 17 patients with AIDS who were neurologically intact (NI-AIDS) who were matched with the ADC subjects by CD4 lymphocyte counts for severity of systemic HIV disease.

MAIN OUTCOME MEASURES

Neuropsychological test performance; z score comparisons were made with the HIV-control group using 2.25-SD cutoffs for abnormality.

RESULTS

Compared with NI-AIDS subjects, performance of patients with mild ADC was markedly worse in the cognitive areas of executive function, memory, and complex attention but not in affect or the cognitive areas of simple motor function, orientation, language, or visuospatial construction. Within the areas of executive function, memory, and complex attention, all of the HIV-controls and 95% of the NI-AIDS subjects had impaired test performance in a maximum of one area only. In marked contrast, 14 (93%) of the 15 patients with mild ADC had abnormal test performances in all three of these cognitive areas. Using a criterion of abnormal performance in at least two of the cognitive areas of executive function, memory, and complex attention, all patients with mild ADC could be differentiated from HIV-controls with 100% sensitivity and specificity and from NI-AIDS subjects matched for disease severity by CD4 lymphocyte count with 100% sensitivity and 94% specificity, which increased to 100% with the requirement of impairment in all three cognitive areas.

CONCLUSIONS

If time constraints or patient compliance limit neuropsychometric testing, examination to detect mild ADC first should be directed to the areas of executive function, memory, and complex attention. This pattern of neuropsychological deficits in patients with mild ADC is suggestive of subcortical dementia.

Computer-administered visual analogue mood scales: rapid and valid assessment of mood in HIV positive individuals

Studies of cognition in patients with the human immunodeficiency virus must take into account the effects of mood. Standardised mood-rating questionnaires are oftentimes consuming and fatiguing for such patients and so may be omitted from experiments. Visual analogue rating scales for affective state are rapidly administered and are quite acceptable to subjects. In 64 HIV seropositive homosexual or bisexual males, measures of anxiety and depression derived from two computer-administered visual analogue scales were compared with anxiety and depression ratings from the Spielberger State-Trait Anxiety Inventory and the Center for Epidemiological Studies-Depression. Analogue ratings of anxiety correlated .80 with STAI State anxiety and .58 with STAI Trait anxiety measures and analogue ratings of depression correlated .78 with CES-Depression measures. Analogue ratings may differentiate situational anxiety and depression more effectively and so are valid tools in assessment of anxiety and depression in HIV seropositive subjects. These may be of particular value when limitations of time or patient illness require a rapid assessment of mood variables in neuropsychiatric research.

Selective impairment of express saccade generation in patients with schizophrenia

When a temporal gap is introduced between the offset of a central fixation point and the onset of a peripheral saccadic target, normal subjects generate an increased number of short latency (90-150 ms) saccades, termed express saccades, and the profile of express saccade frequency across different gap sizes for any individual subject, even if untrained in the task, shows a high test-retest reliability. In patients with schizophrenia, the generation of express saccades was also normal for gap sizes of 200-300 ms or in an overlap task (gap = 0 ms). However, for temporal gaps of 50-150 ms, the generation of express saccades was significantly impaired in the schizophrenic subjects. This selective deficit appeared to be independent of the patients' neuroleptic medication status and did not correlate with the severity of schizophrenic symptoms. It is postulated that the successful execution of an express saccade requires that the cognitive operations of disengagement of visual attention and selection of the appropriate motor command to generate a saccade both be commenced or completed during the temporal gap between fixation offset and peripheral target onset. Our results suggest that, in schizophrenia, there is an impairment in the cortical/subcortical neural network that generates express saccades and controls these cognitive operations. Potential sites for such dysfunction in schizophrenia include the parietal cortex and the GABA-ergic function of the superior colliculus.

Validation of a clinical antisaccadic eye movement test in the assessment of dementia

The ability to generate antisaccades (eye movements deliberately made in the direction opposite to that of a visual stimulus) may be used to assess central nervous system function in a variety of neurologic and psychiatric disorders. However, the usefulness of this paradigm in clinical practice is limited by the need for an oculographic laboratory. We describe a clinical version of such an antisaccadic task and present normative data from 332 subjects. We also examined clinical antisaccades and cognitive performance in 30 patients with Alzheimer's disease, five patients with Huntington's disease, and 12 patients with pseudodementia. In Alzheimer's disease, error rates in the clinical antisaccadic test correlated well with those from a laboratory-based antisaccadic task measured on the same day by infrared oculography, confirming that the clinical antisaccadic test is a valid analog of the more sophisticated laboratory paradigms. Clinical antisaccadic error rates correlated strongly with the severity of dementia in Alzheimer's disease, and correlations with cognitive performance suggested that the clinical antisaccadic test may have some specificity for frontal lobe dysfunction. Patients with pseudodementia had normal clinical antisaccadic error rates, and the test may therefore be of use in differentiating dementia from pseudodementia. This clinical antisaccadic test provides a simple, reliable, and inexpensive quantitative clinical tool that is of value in the assessment of disturbances of higher cortical function.

Tizanidine--initial pharmacokinetic studies in patients with spasticity

The time-course of plasma concentrations of the antispasticity agent tizanidine were measured by a specific radioimmune-assay in six adults who had severe spasticity due to multiple sclerosis. The drug was given as a single oral 4 mg dose to each subject. The drug had a mean absorption half-life of 0.30 +/- 0.155 h following a mean lagtime of 0.361 +/- 0.118 h, and a mean terminal elimination half-life of 4.16 +/- 2.06 h. Only 2.65 +/- 0.82% of the dose was excreted unchanged in urine in 2 h. Calculated values of clearance and apparent volume of distribution were almost certainly overestimates as it seems probable that the orally-administered drug undergoes significant presystemic elimination (its bioavailability was not determined in the investigation here reported). Relief of spasticity, from the dosage used, was relatively slight and appeared greatest at the time of peak plasma levels of the drug.