Working memory control in patients with schizophrenia: a PET study during a random number generation task.

OBJECTIVE: The authors' goal was to investigate brain regions involved in the deficiency of working memory control processes in patients with schizophrenia. METHOD: Regional cerebral blood flow was measured with positron emission tomography in eight men with stabilized schizophrenia and eight healthy men while they were performing a graded random number generation task. Twelve scans were made for each subject. Covariations between randomness of responses and regional activation were analyzed. RESULTS: The pattern of covariation between randomness of responses and activation in the anterior cingulate and superior parietal regions differed between patients and healthy subjects. CONCLUSIONS: These results suggest a cinguloparietal dysfunction underlying the impairment of working memory control processes during a random number generation task in patients with schizophrenia.

Does long-term memory deficit relate to patients' slowness in schizophrenia?

INTRODUCTION: The performance of fast and slow schizophrenic patients and matched controls was examined in a delayed free recall task to assess whether the patient's slowness would influence long-term memory (LTM) in a similar way to working memory. METHOD: Twenty-three schizophrenic patients who met DSM-IV criteria and were matched in age and educational level to 23 controls participated. Subjects' reading rate was measured, and a cut-off of mean controls' reading rate minus 2 standard deviations was allowed the identification of 9 slow patients. The memory task comprised a list of 20 unrelated common words presented visually that were to be recalled in any order after a delay of 25-30 minutes filled with unrelated tasks. RESULTS: The overall patients' performance was poor compared with controls, and slow and fast performance was comparable, contrasting with immediate memory tasks in which slow patients were impaired compared with fast patients. CONCLUSION: Patients' slowness does not seem to influence the long-term memory deficit in schizophrenia.

The state of functioning of working memory in schizophrenia.

The functioning of working memory in schizophrenic patients according to Baddeley's model was examined in two complementary experiments. Experiment 1 comprised 27 patients and their controls, matched in age and level of education. Of this pool, 20 pairs participated also in Experiment 2. Digit span, reading rate, and immediate serial recall assessed the functioning of the phonological loop. Corsi and pattern span tasks assessed the capacity of visuo-spatial memory. The central executive's ability to monitor two concurrent tasks was evaluated in a dual task paradigm, and its capacity to control action in a random generation task. A preliminary set of analyses showed that the patients' performances were reduced in all tasks explored, except in digit span. This initial pattern changed consistently after controlling for reading rate. While slow and fast reading patients were comparable in demographic and clinical criteria, slow reading patients showed impaired performance in all tasks, whereas fast reading patients exhibited reduced performance in visuo-spatial tasks and in the random generation task only. The state of functioning of working memory in schizophrenia appears, therefore, to vary consistently among the components of the model and is markedly impaired in slow reading patients. The implications of slowness are discussed.

Human core temperature minimum can be modified by ambient thermal transients.

By using slow linear thermal transients (+/- 0.025 degree C/min) of reduced amplitude (+/- 3 degrees C around thermoneutrality), we were able to advance the minimum of human internal temperature (Ti) during nocturnal sleep. During experimental night the minimum of esophageal (Tes) and rectal (Tre) temperature were respectively advanced by 1.6 h (P < 0.01) and 2.6 h (P < 0.001) in comparison to reference night spent at thermoneutrality. It must be emphasized that the provoked advance of nocturnal Ti minimum was not accompanied by any change in sleep latency, efficiency, SWS and REM sleep percentages. The result shows that appropriate ambient temperature transient changes could be used to modify the course of human Ti one of the major biological rhythms usually considered as resistant to sleep-wake rhythm manipulation.

Effects of noise on sleep inertia as a function of circadian placement of a one-hour nap.

The purpose of the present study was to analyse the arousing effects of noise on sleep inertia as a function of circadian placement of a one-hour nap. In a first experiment, we measured the effects of sleep inertia in a neutral acoustic environment after a one-hour nap placed either at 0100 or 0400 on response time during a spatial memory test. In a second experiment were analysed the effects of an intense continuous noise on sleep inertia. The results showed that noise produced a total abolition of sleep inertia after an early nap (0000 to 0100). This may be due to the arousing effect of noise; however, results are less clear after a late nap 0300 to 0400 as noise seems to be ineffective. This result is discussed in terms of either a function of time-of-day effect or of prior sleep intensity. Moreover, our data suggest a possible interaction of noise with partial sleep deprivation leading to a slight deleterious effect those subjects who did not sleep at all.

The effects of alcohol on learning as a function of drinking habits.

Thirty-six subjects were categorized as light social drinkers (LSD) and 36 as heavy social drinkers (HSD) on the basis of both biological criteria, gamma-glutamyl transferase (GGT) and the mean corpuscular volume (MCV) and by self-reports of drinking habits. This study examined the effects of alcohol (0.7 ml/kg) and of noise (75 dB(A] on learning and performance, in choice RT and in immediate memory tasks. Each subject was tested in two consecutive sessions (the time factor) under one of the following experimental conditions: (a) silence + placebo; (b) silence + alcohol; (c) noise + placebo; and (d) noise + alcohol. On immediate memory, there was a strong effect of time which interacted with 'drinker' category, suggesting that HSD subjects learn less rapidly than LSD. Time interacted also with state (sober or intoxicated), showing that learning might be impaired even by a moderate dose of alcohol. On the reaction time task no main effects were found but the time X drinker category interaction was significant; in session 1 LSD's RT were shorter than those of HSD. It is suggested that regular heavy drinking might affect the learning abilities of those who are not yet labelled as alcoholics.

The unattended speech effect: perception or memory?

Broadbent (1983) has suggested that the influence of unattended speech on immediate serial recall is a perceptual phenomenon rather than a memory phenomenon. In order to test this, subjects were required to classify visually presented pairs of consonants on the basis of either case or rhyme. They were tested both in silence and against a background of continuous spoken Arabic presented at 75 dB(A). No effect of unattended speech was observed on either the speed or accuracy of processing. A further study required subjects to decide whether visually presented nonwords were homophonous with real words. Again, performance was not impaired by unattended speech, although a clear effect was observed on an immediate serial memory task. Our results give no support to the perceptual interpretation of the unattended speech effect.

Plasma catecholamines and pituitary adrenal hormones related to mental task demand under quiet and noise conditions.

Plasma levels of catecholamines and pituitary adrenal hormones were measured in 20 min samples from eight subjects, in one control session and two experimental sessions, while they performed a short-term memory task under quiet of noise conditions. Performing the task led to significant increase in the plasma levels of cortisol, adrenaline and noradrenaline, whereas no variations in growth hormone and dopamine were observed. Similarly, significant changes occurred in urinary catecholamine excretion. A significant correlation was found between individual plasma cortisol increments and error-rates assessed from an accuracy of recall variable. For adrenaline and noradrenaline, an early response apparently linked with an anticipatory process preceded the task. Exposure to noise did slightly amplify cortisol response to the task, but during the first experimental session, with or without noise, the task elicited greater cortisol increases in all subjects than during the second session. These results provide evidence for a relationship between sympathoadrenocortical activity and attentional demand, whereas cortisol increments seem to be more specifically related to better coping with the task. Frequent hormone level measurements during a prolonged mental task might clarify the complex relationship between time-related bodily hormonal changes, performance and subjective feelings.