Memory performance predicts interrogative suggestibility better than global cognition in older adults with subjective cognitive complaints.

The present study aims to investigate to which extent global cognition and verbal memory can estimate interrogative suggestibility (IS) in elderly people with subjective cognitive complaints (SCCs). We used the Gudjonsson Suggestibility Scale (GSS 2) subscales (i.e., Yield 1, Yield 2 and Shift) as measures of IS. Data from a sample of consecutive patients (N = 94) who referred to neuropsychology units for the first time were collected. Our results showed that verbal memory is a better predictor of IS than global cognition. Moreover, memory impairment led to significantly higher IS independently of global cognitive status. These findings suggest that the assessment of verbal memory allows to estimate individual levels of IS better than global cognition, even in elders with objective cognitive deficits. Implications for forensic assessment of senior witnesses are discussed.

The effect of monocular deprivation on unihemispheric sleep in light and dark incubated/reared domestic chicks.

Unihemispheric sleep is an aspect of the cerebral lateralization of certain species of birds. During sleep, domestic chicks (Gallus gallus) show brief periods of monocular-unihemispheric sleep (Mo-Un sleep): one eye is open and the connected hemisphere is awaken while the other eye remains shut and the connected hemisphere sleeps. The time spent in Mo-Un sleep was investigated following a brief monocular deprivation (MD) in chicks hatched from eggs incubated in darkness and reared in light (D-L), incubated in light and reared in light (L-L) and incubated in darkness and reared in darkness (D-D). The right eye occluded for 12 h in half of chicks and the left eye in the other half. At the end of MD, the Mo-Un sleep was recorded. The effect of MD (total time and time bias) prevailed in determining the pattern of Mo-Un sleep. Chicks showed more time sleeping with the eye/hemisphere that was in control of visual behaviour during MD and opened more time the eye and awake the hemisphere visually deprived. The Mo-Un pattern was not influenced by incubation, rearing, symmetry/asymmetry of visual pathways and imprinting thereby indicating that Mo-Un sleep pattern depends only on the kind of visual experience during wakefulness.

Monocular learning of a spatial task enhances sleep in the right hemisphere of domestic chicks (Gallus gallus).

Unihemispheric sleep is an aspect of cerebral lateralization of birds. During sleep, domestic chicks show brief periods during which one eye is open whilst the other remains shut. In this study, time spent in sleeping and in monocular-unihemispheric sleep (Mo-Un sleep) was investigated following the monocular learning of a spatial discrimination task. Two groups of experimental chicks from day 8 to day 11 post-hatching were trained in a spatial paradigm based on geometrical and topographical clues. One group performed the task with left eye open (LE-chicks), whilst another group performed the task with the right eye open (RE-chicks). LE-chick learned the task, whilst RE-chicks were unable to learn. Time spent in binocular sleep and right Mo-Un sleep (right eye closed and left hemisphere sleeping) was equal in both groups of chicks. Time spent in left Mo-Un sleep (left eye closed and right hemisphere sleeping) was significantly higher in LE-chicks than in RE-chicks. Laterality index reveals that LE-chicks had a significant bias towards more left Mo-Un sleep at any recording day, whilst RE-chicks showed a significant bias towards more right Mo-Un sleep at day 8 and 9 but not at days 10 and 11. RE-chick bias at days 8 and 9 could be attributed to a recovery process in left hemisphere connected to its activation/use effect during trials whilst recovery would be absent at days 10 and 11. LE-chicks bias would be associated with the formation of a spatial memory trace and with a recovery process in right hemisphere.

Local sleep: a spatial learning task enhances sleep in the right hemisphere of domestic chicks (Gallus gallus).

During sleep, domestic chicks (Gallus gallus) show brief and transient periods during which one eye is open while the other remains shut. Electrophysiological recordings showed that the hemisphere contralateral to the open eye exhibited an EEG with fast waves typical of wakefulness, whereas the hemisphere contralateral to the closed eye exhibited an electroencephalogram (EEG) typical of slow-wave sleep. We investigated the time spent in sleep and in monocular-unihemispheric sleep (Mo-Un sleep) following the learning of a spatial discrimination task. A group of experimental chicks from days 8 to 11 post-hatching were trained singly to select one container among four, having a hole on the top (making food available) and positioned in a corner of a rectangular arena. Chicks of the control group did not learn the task because all four containers had a hole on the top and therefore chicks could randomly select any one of them. Experimental and control chicks underwent the same number of trials. Experimental chicks had more total time spent sleeping than control chicks. Experimental chicks spent more time in left Mo-Un sleep, which would be connected with a dominance of the right hemisphere during learning trials. Control chicks showed no eye closure bias at days 8 and 9; however, a slight bias for more right eye closure at days 10 and 11 was observed, suggesting that there was an absence of hemispheric dominance during the first 2 days of control trials and a dominance of the right hemisphere during the last 2 days of control trials. Overall, chicks that learned the spatial task slept significantly more than chicks that were exposed to the experimental paradigm but did not learn the task. This suggests that the Mo-Un sleep pattern showed by experimental chicks is a type of local sleep associated with a process of functional recovery and/or with consolidation of memory in the right hemisphere, which would be mainly engaged during training trials.

Binocular and monocular/unihemispheric sleep in the domestic chick (Gallus gallus) after a moderate sleep deprivation.

Binocular (Bin-sleep) and monocular/unihemispheric sleep (Mo-Un sleep) were studied in domestic chicks (Gallus gallus) after an 8 h period of sleep deprivation. Eleven-day-old chicks were divided into three groups: two non-deprived (N-DEP1 and N-DEP2) and one deprived for 8 h (DEP-8H). Deprivation was performed by placing chicks on a treadmill on which they were forced to walk continuously. Sleep behaviour was recorded for 6 h consecutively immediately after the end of sleep deprivation. During the recovery period, sleep-deprived chicks slept for a longer duration, spent significantly more time in binocular sleep and slept for significantly longer episodes that did control chicks. Regarding Mo-Un sleep, sleep deprivation seems to affect the right hemisphere by reducing the number of episodes and the time spent sleeping with the left eye closed. These results suggest that sleep-deprivation significantly influences the pattern of sleep in domestic chicks allowing for a better recovery.

Monocular sleep following passive avoidance learning in chicks.

Monocular sleep following passive avoidance learning was investigated in young chicks. One group of animals (Experimental Group) was presented with a bead coated with an aversive substance; a second group (Control Group 1) underwent bead presentations as in the Experimental Group but with the bead coated with water rather than with the aversive substance, and a third group (Control Group 2) did not undergo to any bead presentation. Binocular and monocular sleep was recorded during the 8h subsequent the learning (or the control) event. The main results were that (1) the percentage of time spent in binocular sleep and the percentage of episodes of binocular sleep were lower in the Experimental Group that in the Control Groups; (2) the times spent in monocular sleep was higher in the Experimental Group and progressively lower in Control Group 1 and Control Group 2; (3) chicks slept predominantly with their left eye closed, but there was no evidence of specific changes in the opening of their right or left eyes associated with the learning event. The results seem to be compatible with the hypothesis that monocular sleep serves to provide the animal with the possibility to monitor periodically the environment to look for important events (e.g. predators, presence of the mother hen and siblings) and any arousal-producing event that would occur before a sleep episode tends to increase the likelihood of monocular sleeping.

Monocular-unihemispheric sleep and visual discrimination learning in the domestic chick.

During sleep, domestic chicks (Gallus gallus) show brief and transient periods during which one eye is open while the other remains shut. Electrophysiological recordings showed that the hemisphere contra-lateral to the open eye exhibited an EEG with fast waves typical of wakefulness, whereas the hemisphere contra-lateral to the closed eye exhibited an EEG typical of slow wave sleep. We investigated the pattern of monocular-unihemispheric sleep (Mo-Un sleep; i.e. selective preferential closure/opening of the left or right eye during sleep) following three types of visual learning tasks. The first group of chicks was submitted to a colour discrimination task (1), the second group to a spatial discrimination task with colour as a conspicuous, but irrelevant, cue (2), the third group to a spatial task without colour cue. After learning, the amount of binocular sleep and Mo-Un sleep patterns were recorded. The first and the second group of chicks exhibited more right Mo-Un sleep (right eye-closure/left unihemispheric sleep), suggesting that this pattern may be connected with prevalent engagement of left hemisphere during training trials. The third group showed a significant more left Mo-Un sleep (left eye-closure/right unihemispheric sleep) which would be associated with a prevalent engagement of right hemisphere during trials. Chicks of the control groups, did not learn the task, but were submitted to an equal number of trials. Controls of tasks 1 and 2 showed more left Mo-Un sleep suggesting a dominance of right hemisphere during exposure trials. Instead there was no eye-closure bias in controls of task 3, suggesting an absence of hemispheric dominance during trials. It is suggested that the Mo-Un sleep pattern may be a type of local sleep associated with a process of functional recovery in the hemisphere which was mainly engaged during training trials.

Effects of social interaction on monocular/unihemispheric sleep in male and female domestic chicks.

The monocular/unihemispheric sleep was studied in male and female domestic chicks reared socially. In first week post-hatching, chicks were reared in couples whilst during the second week, for half of the chicks the cospecific was maintained (Conspec-chicks) and for the other half the conspecific was removed (No-Conspec-chicks). During the first week, female chicks showed a bias for more left-eye closure/right unihemipheric sleep, whilst male chicks did not show any eye-closure bias. In the second week, both female and male Conspec-chicks showed a bias for right eye-closure/left unihemispheric sleep. Female No-Conspec-chicks did not show any eye-closure bias whilst male No-Conspec-chicks showed a bias for more left eye-closure/right unihemispheric sleep. Based on the role of the avian brain lateralization, a bias for more right or left eye-closure could be associated with a prevalent activation of left or right hemisphere during wakefulness. Eye-opening during sleep might be connected with the hemisphere that was not or was less activated during wakefulness or with lateralization of the environment monitoring against predation.

The effects of early post-hatching changes of imprinting object on the pattern of monocular/unihemispheric sleep of domestic chicks.

The pattern of monocular/unihemispheric sleep (Mo-Un sleep) was studied behaviourally in male and female chicks after early post-hatching changes of the imprinting object. Chicks were reared with an imprinting object on day 1 post-hatching which was removed or changed on day 2. On day 1, time spent in binocular sleep (both eyes closed) was similar in male and female chicks, though the number of episodes was lower in females than in males. There was no eye-closure bias in the pattern of Mo-Un sleep (one eye shut and the other open) in chicks of both sexes. On day 2, chicks subjected to the removal of imprinting object showed less time and number of episodes of binocular sleep than control chicks and chicks subjected to changes of imprinting object. There was no eye-closure bias in control chicks whilst a significant bias for more right Mo-Un sleep was recorded in chicks after removal and changes of imprinting object of both sexes. It is suggested that the removal or changes of imprinting object would cause a decrease of binocular sleep and trigger processes associated to secondary imprinting involving the left hemisphere. The bias for more right Mo-Un sleep (right eye-closure) could be the by-product of consolidation processes of secondary imprinting memories in the left hemisphere and/or of more left eye-opening as a result of periodical awakening of right hemisphere to control the environment after a stressful condition such as the removal or change of imprinting object.

Monocular sleep in male domestic chicks.

Behavioural sleep during the first 2 weeks after hatching was studied in male chicks reared with an imprinting object (I-chicks) and in social isolation (NI-chicks). Time spent in sleeping with both eyes closed (binocular sleep) decreased gradually with age in both I-chicks and in NI-chicks whilst the number of episodes of binocular sleep decreased with age in NI-chicks but not in I-chicks. The pattern of monocular sleep (only one eye closed) of both I-chicks and NI-chicks showed no significant bias towards predominant left- or right-eye closure during the first week. During the second week, I-chicks showed a tendency towards more pronounced left-eye closure with a peak on day 10, whilst NI-chicks showed a tendency for more pronounced right-eye closure with peaks on days 9 and 11. In a different group of chicks, changing the colour of the imprinting object on day 8 produced a shift towards right-eye closure. In contrast, the removal of the imprinting object on day 8 did not cause any change in the pattern of monocular sleep. Differences with respect to sleeping patterns previously observed in females chicks are discussed.

Light exposure of the chick embryo influences monocular sleep.

Together with some aquatic mammals, several species of birds, such as the domestic fowl, exhibit a particular behavioural and electrophysiological state called 'unihemispheric sleep', in which one cerebral hemisphere is awake and the other is sleeping. Slow-wave sleep in one hemisphere is associated with closure of the contralateral eye, whilst the eye contralateral to the awake hemisphere is open; closure of both eyes, in contrast, is associated with bihemispheric slow-wave sleep or with REM sleep. During the last few days of incubation the chick embryo is turned in the egg so that it occludes its left eye, whereas light entering through the shell can stimulate the right eye. We found that in the first 2 days after hatching chicks coming from eggs incubated in the light and reared with an imprinting object slept mostly with their right-eye open, whereas those coming from eggs incubated in the dark slept mostly with their left-eye open. In chicks reared without an imprinting object, in contrast, the effect of incubation extended over the first 2 weeks in females, with dark-incubated chicks showing more pronounced left-eye closure than light-incubated chicks, whereas the effect of incubation was similar to that observed in chicks reared with the imprinting object during the first 2 days post-hatch in males and more variable from day to day thereafter. Asymmetric light stimulation of embryos can thus modulate, though it does not generate, the left-right direction of eye opening during post-hatching monocular sleep; apparently, such a modulation depends on the emotional/motivational state of the animal associated with the outcomes of a naturally occurring visual imprinting.