Attentional abilities and measures of schizotypy: their variation and covariation in schizophrenic patients, their siblings, and normal control subjects

Sustained and selective attention as measures of genetic liability to schizophrenia

We tested for a relationship between attention and genetic liability to schizophrenia. Samples of probands with DSM-IV schizophrenia (n=20), their well first-degree relatives (n=40) and healthy controls (n=82) were tested using measures of sustained attention (degraded-stimulus continuous performance test: DS-CPT) and selective attention (spatial negative priming task). Assuming a liability-threshold model, we predicted that probands would display greater attentional decrements than controls and that the relatives would show intermediate levels of decrement. We did not observe the predicted pattern of effect using either measure, although the probands showed a trend towards less negative priming. However, our results may have been affected by self-selection bias in probands and relatives and clinical heterogeneity among probands, which could have reduced our power to detect effects.

Executive/attentional performance and measures of schizotypy in patients with schizophrenia and in their nonpsychotic first-degree relatives

Previous studies of executive/attentional functions have found impairments in nonpsychotic first-degree relatives of patients with schizophrenia. The aims of this study were: (1) to replicate these findings by three laboratory measures of attention/information processing - a continuous performance test (DS-CPT), a forced-choice span of apprehension task (SPAN), and a digit symbol substitution test (DSST), and by a series of neuropsychological tests sensitive to prefrontal cortical damage - Trail Making A and B, verbal fluency (VFT), Stroop Color and Word Test (Stroop), and Wisconsin Card Sorting Test (WCST); (2) to investigate whether such executive/attentional deficits are associated with schizotypal traits assessed using the social anhedonia, physical anhedonia, perceptual aberration and magical ideation scales (Chapman, L.J., Chapman, J.P., Raulin, M.L. 1976. Scales for physical and social anhedonia. J. Abnorm. Psychol. 85, 374-382; Chapman, L.J., Chapman, J.P., Raulin, M.L., 1978. Body-image aberration in schizophrenia. J. Abnorm. Psychol. 87, 399-407; Eckblad, M., Chapman, L.J., 1983. Magical ideation as an indicator of schizotypy. J. Consult. Clin. Psychol. 51, 215-225). In both patient and relative groups, performance was significantly poorer on the DSST, VFT and Trail B, and the reaction time on the SPAN was significantly longer. These neuropsychological impairments were present as much in siblings as in parents of schizophrenic patients; age did not appear to cancel differences between the relative and control groups. In the relative group, the four scores of schizotypy were at an intermediate level between those of patient and control groups, and the social anhedonia and perceptual aberration scores tended to be significantly different between the relative and the control groups. Only two significant correlations were found between the neuropsychological performance and the measures of schizotypy.

Is the attentional dysfunction in schizotypy related to anxiety?

Two factors, 'anxiety-loaded' (AL) and 'perceptual-disorganization' (PD), emerged in a factor analysis of the Schizotypal Personality Questionnaire (SPQ). Sixty of the 219 participants performed a latent inhibition (LI) task. During the pre-exposure phase, one group was exposed to repeated non-reinforced presentations of an irrelevant stimulus and the other was not pre-exposed. In the subsequent test phase, learning was slower in the pre-exposed group than in the non-pre-exposed group. The LI effect was assessed, separately, as a function of SPQ, trait-anxiety sub-scale (TASS) of the State and Trait Anxiety Inventory (STAI), and AL and PD factors scores. LI was disrupted in participants with either high scores on SPQ, STAI, or the AL factor. A regression analysis indicated that both TASS and SPQ independently accounted for LI disruption in high schizotypals, but that the contribution of TASS was stronger. It was suggested that the anxiety component of schizotypy, more than the perceptual-disorganization (schizophrenia-like) component, accounts for the attentional dysfunction in high schizotypals, and for their greater than normal distraction by irrelevant stimuli.

Smooth pursuit eye tracking and visual fixation in psychosis-prone individuals

Subjects identified by Perceptual Aberration-Magical Ideation (Per-Mag) scores (n=97), Social Anhedonia (SocAnh) scores (n=45), and Physical Anhedonia (PhysAnh) scores (n=31) as well as normal controls (n=94), underwent psychophysiological and clinical assessment. This is the first published investigation of pursuit system functioning in three groups of questionnaire-identified at-risk individuals. Pursuit during a simple non-monitor tracking task was measured using root-mean-square error (RMSE) scores and pursuit gain scores. Fixation performance was measured in terms of number of saccades away from the central fixation point. The at-risk subjects were more likely to display aberrant smooth pursuit tracking than controls, though there were no significant differences between the at-risk subjects endorsing items relevant to positive-symptom schizotypy and those endorsing items pertaining to negative-symptom schizotypy. The groups did not differ significantly in their visual fixation performance. Participants were also evaluated for the presence of Axis I symptomatology and psychotic-like experiences. Neither the experimental subjects nor the control subjects displayed a significant association between ocular motor performance and psychotic-like experiences. These findings are consistent with prior evidence that pursuit tracking is a trait characteristic, independent of clinical status.

Attentional deficits in patients with schizophrenia and in their non-psychotic first-degree relatives

The aim of this study was to investigate whether non-psychotic relatives of schizophrenic probands have deficits in sustained attention as measured by the Continuous Performance Test, Identical Pairs version (CPT-IP) and whether such deficits are associated with negative schizotypal personality disorders. The study subjects were 23 schizophrenic probands, 45 of their first-degree relatives and 36 normal controls. For each subject, attention was assessed during five conditions (2 standard, 2 slow, 1 easy) of visual stimuli (numbers and shapes). Schizotypy status was determined with the physical anhedonia and social anhedonia scales of Chapman et al. (Chapman, L.J., Chapman, J.P., Raulin, M.L., 1976. Scales for physical and social anhedonia. Journal of Abnormal Psychology 42, 374-382). The CPT-IP sensitive index d' in the standard shape condition was significantly lower in schizophrenics and in their relatives than in controls. For all d' values, the percentage of impaired first-degree relatives was at an intermediate level between patients and control individuals. Furthermore, the schizophrenic probands made more random errors in the standard and in the slow number conditions than the other two groups. None of the schizotypy measures correlated with the CPT-IP deficits. These results suggest that spatial sustained attention deficit may be a vulnerability marker for schizophrenia; however, this deficit and the negative dimension of schizotypal personality disorders may be distinct traits.

Vigilance in schizophrenia and its disruption by impaired pre-attentive selection: a dysintegration hypothesis

INTRODUCTION

The study determined, simultaneously, whether major deficits of schizophrenia (sustained and selective attention, slow information processing, slow motor responding) are independent or related to each other.

METHODS

An auditory vigilance task (Pigache Attention Task, PAT) required a button-press to targets during four 5-minute subtests (slow diotic, fast diotic, slow dichotic, fast dichotic, analogous to four versions of the continuous performance test). Twenty schizophrenics on the first test-occasion of a double-blind, placebo controlled, crossover study were compared to 11 healthy subjects. Also, all 28 fortnightly test occasions were analysed to quantify the schizophrenia deficits more precisely and the PAT was evaluated in a larger group of 86 healthy subjects.

RESULTS

Schizophrenics were significantly impaired on all task parameters versus healthy subjects. The patients' errors were independent and additive (grand mean components: basic task 36%, including a 9% time-on-task component; speed increment 26%; dichotic increment 38%). Errors, latencies, and psychosis severity were mutually correlated.

CONCLUSIONS

The performance of all subjects confirmed a quantitative Vigilance Decision Model. The PAT impairments in schizophrenia suggested that rival options (e.g. thoughts) redeployed or suppressed attention away from the task , indicating a dysfunction of pre-attentive selection processes. Brain mechanisms are discussed and a new dys integration hypothesis of schizophrenia is proposed.

Effects of smoking status and schizotypy on latent inhibition

Two experiments investigated the effects of smoking status and schizotypy on the ability to gate out irrelevant information as assessed in auditory and visual latent inhibition (LI), Stroop effect and negative priming. The two experiments used 10 or 30 pre-exposures for auditory LI and a long or short interstimulus interval for the Stroop task, respectively, which included negative priming and served as masking task for the visual LI. Smoking status did not affect performance on any of the tasks, except for auditory LI after 30 pre-exposures, which was enhanced. The relationship between schizotypy and cognitive performance was complex. In Experiment 1, high schizotypals had smaller visual LI and negative priming than low schizotypals, whereas in Experiment 2 the reverse was observed, namely, larger LI and negative priming in high schizotypals.

Alpha-linolenic acid deficiency modifies distractibility but not anxiety and locomotion in rats during aging

In rodents, chronic dietary alpha-linolenic acid deficiency decreases learning and memory and alters dopaminergic and serotoninergic neurotransmission. However, these two neurotransmitter systems are related mainly to attention, emotion and locomotion. Therefore, we decided to investigate the effects of dietary alpha-linolenic acid deficiency in rats tested with animal models of distractibility (the distractometer procedure), anxiety (the elevated plus maze) and ambulatory activity (a circular corridor). Moreover, because these neurochemical modifications persist during aging, we decided to study the effects of aging on these behaviors by using rats aged 2, 6, 12 and 24 mo. An age-related decline in distractibility was observed that was accelerated by linolenic acid deficiency. Indeed, an age-related reduction in distractibility was found in so far as distraction time was reduced at the age of 12 mo in controls and at the age of 24 mo in deficient groups compared with 2-mo-old rats. Moreover, distraction time was significantly lower in 6- and 24-mo-old rats fed a deficient diet compared with age-matched controls. Anxiety was not modified by diet or age. Finally, a parallel decrease in locomotion was exhibited by rats fed both diets between 6 and 12 mo of age. Locomotion was not modified by diet. These results show that dietary alpha-linolenic deficiency alters behavior in a very specific way; distractibility is modified by diet, whereas anxiety and locomotion are not, suggesting that particular brain areas may be altered.

A rat model of distractibility: effects of drugs modifying dopaminergic, noradrenergic and GABAergic neurotransmission

A procedure for analyzing effects of drugs on distractibility is proposed. Rats are trained to traverse a straight runway with a sucrose solution as reinforcement. Once the response has been acquired, an additional runway ending in an empty box is connected. The time spent investigating this additional runway is the measure of distractibility. Amphetamine, 1 mg/kg i.p., increased distractibility. In rats that were never reinforced, amphetamine at a dose of 1 mg/kg reduced the time spent in the additional runway. This shows that the effects of amphetamine in the reinforced animals cannot be interpreted as enhanced exploration. Furthermore, the benzodiazepines diazepam (2 and 4 mg/kg, i.p.) and chlordiazepoxide (2.5, 5 and 10 mg/kg, i.p.), known to enhance exploration of novel environments, did not affect the time spent in the additional runway in sucrose-reinforced animals. It was concluded that the procedure indeed is a model of distractibility. The dopamine antagonist cis(Z)-flupenthixol, at a dose of 0.25 mg/kg, i.p., blocked the effects of amphetamine, 1 mg/kg. Flupenthixol itself, in doses of 0.25 and 0.5 mg/kg, did not affect the time spent in the additional runway. This suggests that enhanced dopaminergic activity indeed is responsible for the effects. This proposal is further supported by experiments showing that the noradrenaline precursor dihydroxyphenylserine (10 mg/kg + carbidopa, 50 mg/kg, both i.p.) and the noradrenergic neurotoxin DSP4 (50 mg/kg, i.p.) had no effect on distractibility. Moreover, amfonelic acid, a dopamine releaser with slight or no effect on noradrenergic neurotransmission, had effects very similar to those of amphetamine when given in doses of 0.25 and 0.5 mg/kg, i.p. A lower dose, 0.125 mg/ kg, was ineffective. Taken together, these data suggest that enhanced dopaminergic neurotransmission increases distractibility in the rat. However, both amphetamine and amfonelic acid may stimulate serotonin release. Until serotonergic drugs have been tested, a contribution of this transmitter cannot be ruled out. The distraction procedure may constitute an animal model of some kinds of disordered information processing.

Conditioned blocking in patients with paranoid, non-paranoid psychosis or obsessive compulsive disorder: associations with symptoms, personality and monoamine metabolism

Conditioned blocking (CB) refers to a delay in learning that a new stimulus, added during learning, has the same consequences as the conditioned stimulus already present. In animals such "learned inattention" depends on monoaminergic and limbic function and, thus, CB performance should be informative on selective information processing impairments found in subgroups of psychotic patients. Attenuated CB in acute schizophrenia has been reported to normalize rapidly. This study examines in young patients the specificity of CB performance to illness, and its associations with symptoms, personality traits and monoaminergic metabolic status. CB was attenuated in psychotic patients with non-paranoid symptoms (NP: n = 12, mean age 17 years) with respect to obsessive-compulsive (OCD: n = 13, mean age 16 years) and healthy subjects (CON, n = 29, mean age 18 years), but only a transient attenuation was observed in paranoid hallucinatory patients (PH: n = 14, mean age 19 years). Outgoing personality traits in CON and OCD subjects correlated with CB. In NP patients attenuated CB was associated with increasing neurotic lability. In PH patients CB correlated positively with "manic" but negatively with psychotic or neurotic scores. The severity of negative symptoms in psychosis and specific negative/positive symptoms in the NP/PH groups was associated with reduced CB. Increased dopamine activity (24-h urine samples) correlated positively with CB, but relative increases of noradrenaline metabolism in NP and serotonin metabolism in OCD patients interfered. In summary, marked psychotic or neurotic traits and some symptom-states were associated with reduced CB. The particular selective processing problems of NP patients may reflect inappropriate NA activity.