Efectos del sobrepeso y la obesidad en las funciones cognitivas de niños y adolescentes / Effects of overweight and obesity on cognitive functions of children and adolescents

Introducción. Investigaciones recientes sugieren que el sobrepeso y la obesidad en niños y adolescentes afectan a los procesos cognitivos y pueden alterar el aprendizaje escolar. En particular, las denominadas funciones ejecutivas, como la capacidad de inhibición de la respuesta, el control de la impulsividad, la flexibilidad cognitiva, la planificación y la toma de decisiones, se han relacionado de forma inversa con el índice de masa corporal. Objetivo. Este trabajo pretende examinar las hipótesis neurobiológicas y psicológicas que explican por qué el sobrepeso y la obesidad alteran las funciones cognitivas de niños y adolescentes. Desarrollo. Las dietas ricas en grasas y azúcares pueden provocar hiperinsulinemia, dislipidemia, hipertensión, aumento del tejido adiposo abdominal y resistencia a la insulina y a la leptina. Estas alteraciones metabólicas inducen un proceso inflamatorio sistémico periférico que puede afectar a la barrera hematoencefálica y al funcionamiento cerebral de regiones vinculadas a los procesos de atención y de aprendizaje y memoria. Algunos trastornos metabólicos de la madre gestante, la obesidad durante el embarazo y las experiencias traumáticas pre- y posnatales pueden desencadenar cambios en el control de la ingesta de comida en niños y adolescentes e inducir sobrepeso en sus etapas críticas del desarrollo. La obesidad afecta al funcionamiento del hipocampo y produce disminución de la sustancia gris de la corteza prefrontal, modificando con ello las capacidades cognitivas, especialmente las funciones ejecutivas. Conclusiones. El sobrepeso y la obesidad en la infancia y la adolescencia son un factor de riesgo no sólo para la salud general, sino también para el correcto desarrollo cerebral y de las funciones cognitivas, y pueden, por tanto, conducir al fracaso escolar.(AU)

Introduction. Recent findings suggest that overweight and obesity in children and adolescents affect cognitive processes and can alter school learning. The so-called executive functions, such as response inhibition capacity, impulsivity control, cognitive flexibility, planning, and decision making, have been inversely related to body mass index. Aim. This work aims to examine the neurobiological and psychological hypothesis that explain why overweight, and obesity alter the cognitive functions of children and adolescents. Development. Diets rich in fats and sugars can cause hyperinsulinemia, dyslipidemia, hypertension, augmented abdominal adipose tissue and resistance to insulin and leptin. These metabolic alterations induce a peripheral systemic inflammatory process that can affect the blood-brain barrier and the brain functioning of regions linked to attention and learning and memory processes. Some metabolic disorders of the pregnant mother, obesity during pregnancy and pre- and postnatal traumatic experiences can trigger changes in the control of food intake in children and adolescents and induce overweight in critical stages of their development. Obesity affects the functioning of the hippocampus and produces a decrease in the prefrontal cortex gray matter, thereby modifying cognitive abilities, especially executive functions. Conclusions. Overweight and obesity in childhood and adolescence are a risk factor not only for general health but also for proper brain development and cognitive functions and can therefore lead to school failure.(AU)

[Effects of overweight and obesity on cognitive functions of children and adolescents]. / Efectos del sobrepeso y la obesidad en las funciones cognitivas de niños y adolescentes.

INTRODUCTION: Recent findings suggest that overweight and obesity in children and adolescents affect cognitive processes and can alter school learning. The so-called executive functions, such as response inhibition capacity, impulsivity control, cognitive flexibility, planning, and decision making, have been inversely related to body mass index. AIM: This work aims to examine the neurobiological and psychological hypothesis that explain why overweight, and obesity alter the cognitive functions of children and adolescents. DEVELOPMENT: Diets rich in fats and sugars can cause hyperinsulinemia, dyslipidemia, hypertension, augmented abdominal adipose tissue and resistance to insulin and leptin. These metabolic alterations induce a peripheral systemic inflammatory process that can affect the blood-brain barrier and the brain functioning of regions linked to attention and learning and memory processes. Some metabolic disorders of the pregnant mother, obesity during pregnancy and pre- and postnatal traumatic experiences can trigger changes in the control of food intake in children and adolescents and induce overweight in critical stages of their development. Obesity affects the functioning of the hippocampus and produces a decrease in the prefrontal cortex gray matter, thereby modifying cognitive abilities, especially executive functions. CONCLUSIONS: Overweight and obesity in childhood and adolescence are a risk factor not only for general health but also for proper brain development and cognitive functions and can therefore lead to school failure.

TITLE: Efectos del sobrepeso y la obesidad en las funciones cognitivas de niños y adolescentes.Introducción. Investigaciones recientes sugieren que el sobrepeso y la obesidad en niños y adolescentes afectan a los procesos cognitivos y pueden alterar el aprendizaje escolar. En particular, las denominadas funciones ejecutivas, como la capacidad de inhibición de la respuesta, el control de la impulsividad, la flexibilidad cognitiva, la planificación y la toma de decisiones, se han relacionado de forma inversa con el índice de masa corporal. Objetivo. Este trabajo pretende examinar las hipótesis neurobiológicas y psicológicas que explican por qué el sobrepeso y la obesidad alteran las funciones cognitivas de niños y adolescentes. Desarrollo. Las dietas ricas en grasas y azúcares pueden provocar hiperinsulinemia, dislipidemia, hipertensión, aumento del tejido adiposo abdominal y resistencia a la insulina y a la leptina. Estas alteraciones metabólicas inducen un proceso inflamatorio sistémico periférico que puede afectar a la barrera hematoencefálica y al funcionamiento cerebral de regiones vinculadas a los procesos de atención y de aprendizaje y memoria. Algunos trastornos metabólicos de la madre gestante, la obesidad durante el embarazo y las experiencias traumáticas pre- y posnatales pueden desencadenar cambios en el control de la ingesta de comida en niños y adolescentes e inducir sobrepeso en sus etapas críticas del desarrollo. La obesidad afecta al funcionamiento del hipocampo y produce disminución de la sustancia gris de la corteza prefrontal, modificando con ello las capacidades cognitivas, especialmente las funciones ejecutivas. Conclusiones. El sobrepeso y la obesidad en la infancia y la adolescencia son un factor de riesgo no sólo para la salud general, sino también para el correcto desarrollo cerebral y de las funciones cognitivas, y pueden, por tanto, conducir al fracaso escolar.

Caloric restriction modulates the monoaminergic system and metabolic hormones in aged rats.

Caloric restriction (CR) can attenuate the general loss of health observed during aging, being one of the mechanisms involved the reduction of hormonal alteration, such as insulin and leptin. This change could also prevent age-specific fluctuations in brain monoamines, although few studies have addressed the effects of CR on peripheral hormones and central neurotransmitters exhaustively. Therefore, the variations in brain monoamine levels and some peripheral hormones were assessed here in adult 4-month old and 24-month old male Wistar rats fed ad libitum (AL) or maintained on a 30% CR diet from four months of age. Noradrenaline (NA), dopamine (DA), serotonin (5-HT) and its metabolites were measured by high-performance liquid chromatography with electrochemical detection (HPLC-ED) in nine brain regions: cerebellum, pons, midbrain, hypothalamus, thalamus, hippocampus, striatum, frontal cortex, and occipital cortex. In addition, the blood plasma levels of hormones like corticosterone, insulin and leptin were also evaluated, as were insulin-like growth factor 1 and other basal metabolic parameters using enzyme-linked immunosorbent assays (ELISAs): cholesterol, glucose, triglycerides, albumin, low-density lipoprotein, calcium and high-density lipoprotein (HDLc). CR was seen to increase the NA levels that are altered by aging in specific brain regions like the striatum, thalamus, cerebellum and hypothalamus, and the DA levels in the striatum, as well as modifying the 5-HT levels in the striatum, hypothalamus, pons and hippocampus. Moreover, the insulin, leptin, calcium and HDLc levels in the blood were restored in old animals maintained on a CR diet. These results suggest that a dietary intervention like CR may have beneficial health effects, recovering some negative effects on peripheral hormones, metabolic parameters and brain monoamine concentrations.

[Caloric restriction and memory during aging]. / Envejecimiento y memoria: efectos de la restriccion calorica.

INTRODUCTION: To understand the underlying brain mechanisms involved in the aging process and mental deterioration could be key to the development of behavioral patterns that guarantee reaching advanced ages with the highest possible quality of life and reduce the cognitive loss associated with senescence. AIM: To describe and analyze different animal and human studies that demonstrate that a caloric restriction diet may rescue cerebral aging and the cognitive decline associated to aging. DEVELOPMENT: For more than 100 years it has been known that caloric restriction extends life span in many laboratory animal. This effect seems to derive from the reduction of age-related symptoms, such as obesity, the onset of cancerous tumors and some metabolic diseases. However, while the consequences of caloric restriction on health are well-established, their ability to reverse age-dependent memory deficits remains a controversial issue. The analyses of the effects of caloric restriction on different animals provides progress for the understanding of its beneficial effects on the neurobiology of cognitive processes during aging. CONCLUSIONS: Caloric restriction attenuates the normal or pathological aging of the brain and reduces age-related memory problems. Dietary intervention could become a very effective method to promote a better quality of life and prevent the age-related cognitive deficits.

TITLE: Envejecimiento y memoria: efectos de la restriccion calorica.Introduccion. El conocimiento de los mecanismos cerebrales involucrados en el proceso de envejecimiento y el deterioro mental podria ser clave para el desarrollo de pautas de conducta que garanticen alcanzar edades avanzadas con la maxima calidad de vida posible y reducir la perdida cognitiva asociada a la senectud. Objetivo. Describir y analizar diferentes investigaciones con animales y humanos que demuestran que una dieta con restriccion calorica aminora el envejecimiento cerebral y el declive cognitivo asociados a la edad. Desarrollo. Desde hace mas de 100 años se conoce que la restriccion calorica incrementa la longevidad de los animales de laboratorio. Este efecto parece derivar de la disminucion de algunos sintomas que acompañan al envejecimiento, como la obesidad, la aparicion de tumores cancerigenos y algunas enfermedades metabolicas. Sin embargo, mientras las consecuencias de la restriccion calorica sobre la salud estan bien determinadas, su capacidad para frenar el declive cognitivo que acompaña al envejecimiento sigue siendo un tema controvertido. La investigacion de los efectos de la restriccion calorica en animales de laboratorio proporciona los primeros avances para la comprension de sus efectos beneficiosos en la neurobiologia de los procesos cognitivos durante el envejecimiento. Conclusiones. La restriccion calorica atenua el envejecimiento normal o patologico del cerebro y reduce los problemas de memoria asociados a la vejez. La intervencion dietetica podria convertirse en un metodo muy eficaz para fomentar una mejor calidad de vida y prevenir el deficit cognitivo que acompaña a la ancianidad.

Nucleus basalis magnocellularis electrical stimulation facilitates two-way active avoidance retention, in rats.

We studied the effects of post-training intracranial electrical stimulation of the nucleus basalis magnocellularis on two-way active avoidance retention. After the acquisition, rats were stimulated for 20 min, and they were tested again after 24 h or 11 days. The treatment improved memory consolidation, especially in animals with a low initial learning ability. These facilitative effects could be attributed to an enhancement of cortical and/or amygdala activation, leading to an improvement in associative processes and/or cortical plasticity.

Differential effects of parafascicular electrical stimulation on active avoidance depending on the retention time, in rats.

To evaluate whether electrical stimulation of the parafascicular nucleus of the thalamus can improve short-term (24 h) and/or long-term (11 days) retention of two-way active avoidance, rats were implanted with an electrode at this nucleus (experimental groups with stimulation in the parafascicular, and control groups without stimulation) or above it (other control groups without stimulation). After a single 30-trial acquisition session, experimental groups were submitted to a 20-min session of electrical stimulation. Results showed that parafascicular stimulation improved the 24-h retention of the task (number of avoidances made), increasing also the percentage of subjects that achieved a learning criterion and reducing the number of trials needed to reach it. In contrast, no differences among groups were found on the 11-day retention test. The present results agree with previous data showing a short-term effect of parafascicular stimulation on retention, and confirm its involvement in learning and memory modulation. These data are discussed in the context of the acceleration and strengthening of the memory by activation of arousal systems, and/or specific cortical-striatal systems.

Intracranial self-stimulation in the parafascicular nucleus of the rat.

A behavioral analysis of intracranial self-stimulation was provided for parafascicular nucleus. To evaluate whether intracranial self-stimulation in this nucleus could be site-specific and to determine if the positive sites are the same parafascicular areas that facilitate learning when stimulated, rats were tested via monopolar electrodes situated throughout the parafascicular nucleus. Animals were trained to self-stimulate by pressing a lever in a conventional Skinner box (1-5 sessions). Twenty-two of the 42 animals included in the study, had the electrode at the parafascicular nucleus. Only two of them showed intracranial self-stimulation. Histological analyses indicated that the latter rats had the electrode implanted at the anterior area of the medial parafascicular. Other two animals also showed intracranial self-stimulation but they had the electrode in a more posterior brain region, between the Dark-schewitsch nucleus and the red nucleus. The animals implanted at the parafascicular showed higher response rates than the other two rats. These results confirm that: (a) the anterior region of the medial parafascicular is a positive site for stable and regular intracranial self-stimulation behavior, and (b) these positive sites do not coincide with the parafascicular regions related to learning improvement.

The parafascicular nucleus and two-way active avoidance: effects of electrical stimulation and electrode implantation.

To evaluate whether electrical stimulation of the parafascicular nucleus (PF) can improve short-term (24 h) and/or long-term (21 days) retention of two-way active avoidance, rats were implanted with an electrode at this nucleus (experimental groups) or above it (control groups). After a single 30-trial acquisition session, experimental groups were submitted to a 10-min session of electrical stimulation. Results showed that the simple implantation of an electrode at the posterior PF enhanced by itself the acquisition of two-way active avoidance, in such a way that the subsequent stimulation of this region may have been unable to further improve the performance of the rats. On the other hand, parafascicular stimulation improved the 24-h retention of the task in a site-specific way, since this effect was mainly seen after stimulation of the central PF region. The facilitative effect on 24-h retention could also depend on the level of performance achieved during the acquisition session, because this improvement was only evidenced in poorly learning animals. No effects were found on 21-day retention. The present results confirm the involvement of the PF in learning and memory and the functional heterogeneity of this nucleus.

Involvement of the parafascicular nucleus in the facilitative effect of intracranial self-stimulation on active avoidance in rats.

To evaluate whether parafascicular nucleus (PF) is involved in the facilitative effect of lateral hypothalamic intracranial self-stimulation (LH-ICSS) on two-way active avoidance acquisition (5 sessions, 10 trials each, one daily) and long-term retention (10 days), rats were lesioned bilaterally at the PF and implanted with an electrode aimed at the LH to obtain ICSS behavior. After each acquisition session rats were allowed to self-administer 2500 trains of LH-ICSS. The main results were: (1) LH-ICSS facilitated the acquisition and retention of conditioning; (2) PF lesions impaired both acquisition and retention of two-way active avoidance; (3) there was a positive relationship between PF lesions size and learning disruption, and (4) LH-ICSS failed to facilitate learning when PF was lesioned. We concluded that the lesion size is a critical variable to evaluate the effects of PF lesions on learning and memory, and that LH-ICSS treatment may exert their effects through the PF nucleus or, at least, the integrity of PF is required for LH-ICSS to improve clearly the task.

Differential site-specific effects of parafascicular stimulation on active avoidance in rats.

To study the effects of parafascicular intracranial electrical stimulation (PF ICS) on two-way active avoidance acquisition (five training sessions of ten trials each, one session per day) and long-term retention (one session of ten trials), two experiments were carried out. Experiment I tested if posttraining PF ICS can differentially affect the conditioning, depending on the stimulated region of the nucleus. Results indicated that rats stimulated at the posterior region of the parafascicular nucleus (PF) showed a better acquisition than those stimulated at the central one. Experiment II evaluated the effects of the stimulation at the medial, lateral and posterior parts of the PF area on the same task. Results showed that medial and lateral PF ICS disrupted two-way active avoidance, and that posterior PF ICS enhanced the long-term retention of the conditioning. These results suggest a possible role of the PF in modulatory processes of learning and memory, confirming that this nucleus is functionally heterogeneous. Potential facilitative effects are discussed in terms of the relations of the PF to the arousal system and the subparafascicular thalamic nucleus. Disruptive effects are discussed based on the relations of the PF with the 'motor' and 'associative-limbic' basal ganglia circuits.

Facilitatory effects of thalamic reticular nucleus lesions on two-way active avoidance in rats.

Two experiments were performed in order to study the effects of lesions of the rostral thalamic reticular nucleus (Rt) on two-way active avoidance. Male Wistar rats were subjected to either a bilateral electrolytical lesion of the rostral Rt or to control procedures. After recovery, all rats were trained in either a distributed (five training sessions, ten trials each; experiment I) or a massed (a single 30-trials session; experiment II) two-way, active-avoidance task. The level of long-term retention of the task was assessed 10 days later. Lesioned rats showed an overall higher performance than control rats both in experiment I (with lesions affecting the rostral Rt and small portions of some adjacent nuclei) and in experiment II (with lesions almost restricted to the rostral Rt). In contrast, detrimental effects on other tasks have been reported in the literature. Although it cannot be ruled out that those differences might be due to methodological factors, they also might be indicative of an action of rostral Rt lesions on certain mechanisms (either indirectly or directly related to information processing) that could be differentially required depending on the kind of learning task. The latter possibility is discussed in terms of the role played by this nucleus as a modulator of thalamocortical transmission, attentional mechanisms and cortical arousal.

Effects of habenular lesions upon two-way active avoidance conditioning in rats.

To evaluate if habenular nuclei lesions improve, impair, or have no effects on two-way active avoidance acquisition and/or retention, rats in a Lesion group were subjected to bilateral electrolytical lesions of this complex, while control rats were sham-operated (Sham group). Once recovered from the stereotaxic procedures, rats were submitted to 5 training sessions (10 trials each, one session per day) of two-way active avoidance conditioning. Ten days after the last training session, another session was administered in order to test the long-term retention of the task. Results indicated that habenular lesions did not affect the overall performance of the rats during either the acquisition sessions or the retention session of two-way active avoidance. We suggest that habenular lesions can affect the acquisition of several learning tasks, probably through their role in modulating stress responses and/or arousal states. The nature of these effects (whether facilitative, detrimental, or neutral) might depend on the interaction between several factors such as the kind of task, the specific conditioning procedures (which may generate different stress levels), and the specific area destroyed by the lesion.

Tuberomammillary nucleus lesion facilitates two-way active avoidance retention in rats.

To evaluate whether the tuberomammillary nucleus might be involved in the acquisition and/or retention of a two-way active avoidance conditioning, rats were given a unilateral lesion of the tuberomammillary nucleus (E2 region) 24 h prior to the first conditioning session. Four learning sessions were performed: one acquisition and 3 retention sessions (short-term, 24 h; and long-term, 8 and 18 days). Results showed that the lesion facilitated the long-term retention of conditioning, but no effects were observed on acquisition and short-term retention. Since rewarding intracranial electrical stimulation seems to be a consistent way to facilitate learning and memory processes, and tuberomammillary lesion has been shown to improve intracranial self-stimulation behavior (ICSS), we suggest that lesions in the present experiment could have facilitated two-way active avoidance retention by enhancing the function of brain reward mechanisms.

Effects of pretraining paradoxical sleep deprivation upon two-way active avoidance.

In order to study whether paradoxical sleep (PS) is necessary to prepare subjects for the subsequent learning of a distributed two-way active avoidance conditioning, 10 rats were subjected to 5 h of paradoxical sleep deprivation (PSD group) by means of the platform method immediately before each of 5 acquisition sessions (one daily), as well as before a long-term retention (LTR) session (14 days). Another group of rats (PSD control group; n = 10) were placed on large platforms as a control for the side effects induced by PSD platforms. Rats in the dry control group (n = 10) did not receive any treatment. The number of avoidances of the PSD group was significantly lower on the 1st, 2nd and 3rd acquisition sessions compared to the PSD control group, and on the 2nd and 3rd sessions compared to the dry control group. PSD rats made significantly less intertrial crossings than dry controls on the 2nd and 3rd acquisition sessions, but no significant correlations were found between this variable and the number of avoidances. Therefore, our results are not fully in contradiction with the hypothesis that PS previous to the training sessions might prepare the animal for subsequent learning, although the influence of locomotor changes upon the performance of PSD subjects cannot be fully rejected.

Effects of parafascicular electrical stimulation and lesion upon two-way active avoidance in rats.

To evaluate a possible role of the parafascicular nucleus (PF) in modulating distributed two-way active avoidance acquisition and long-term retention (LTR), we designed two experiments. Experiment I was aimed at checking whether posttraining PF intracranial electrical stimulation (PF ICS) can improve the acquisition and/or the LTR of the task. All subjects (Ss, male Wistar rats) were implanted with an electrode at the PF. After each learning session two groups of Ss were stimulated for 10 (ICS-10 group) and 5 (ICS-5 group) min, respectively. A Control group never received PF ICS, while Ss in an ICS-Control group received PF ICS only during a previous search for a nonconvulsive current intensity. Unexpectedly, the ICS-Control group showed poor performance of the task compared to the remaining groups. Since the histological analyses showed that the pretraining ICS treatment produced some PF tissue lesion, Experiment II was aimed at evaluating the effects upon the same task of (1) pretraining PF electrolytical lesions (PF-Lesion group) and (2) posttraining PF ICS treatment (ICS group) at a lower current intensity and without a previous search for nonconvulsive current intensity. PF pretraining lesion decreased conditioning, while posttraining PF ICS did not affect it. We concluded that PF could have a modulatory role in acquisition, and might also contribute to posttraining consolidation, of a distributed two-way active avoidance.

Facilitatory and detrimental effects of parafascicular electrical stimulation upon two-way active avoidance conditioning in rats.

To evaluate whether post-training parafascicular intracranial electrical stimulation (PF ICS) can improve acquisition (five sessions, one daily, 10 trials each) and long-term retention (LTR) (one session, 10 trials) of two-way active avoidance conditioning in rats, experimental subjects (Ss) were implanted with an electrode at the parafascicular nucleus (PF). Control Ss were sham operated without implanted electrodes. Immediately after each acquisition session Ss in the experimental groups were stimulated in the PF during 2- or 10-min periods. After histological analyses Ss were grouped according to the antero-posterior PF stereotaxic coordinates for the electrode tip locations. Ss stimulated at the posterior PF area improved acquisition and the central PF area showed detrimental effects upon conditioning. Electrical stimulation of the anterior PF area did not affect conditioning performance. We conclude that PF appears to have differential modulatory roles in acquisition and retention of two-way active avoidance depending on the PF area involved.

Facilitation of shuttle-box avoidance by the platform method: effects of conditioned stimulus duration.

To evaluate whether the duration of the conditioned stimulus (CS) influences the facilitatory effect of posttraining platform treatment upon the acquisition and long-term retention (LTR) of a shuttle-box conditioning, rats were assigned to one of the four following treatments: P-3 group rats were subjected to a 5-h treatment on 16 cm diameter platforms immediately after each of 5 training sessions (10 trials each separated by 24-h intervals) in which the CS consisted of a tone lasting 3 s; control-3 rats were trained the same way but were not subjected to the platform treatment; P-10 rats did also receive the immediate 5-h treatment on platforms, but the CS was a tone lasting 10 s; finally, control-10 rats did not receive any treatment and were also trained with a 10-s tone. Ten days after training, all rats were also tested for LTR (1 session of 10 trials). When the CS duration was 3 s, the platform treatment improved both the acquisition and LTR of the task, compared to control subjects, but the same treatment had no effect when the CS lasted 10 s. With the use of a 10-s CS, the level of learning achieved by both treated and untreated subjects was similar to the final level of acquisition reached by treated subjects trained with a 3-s CS. We conclude that the facilitatory effects of the platform method treatment upon the acquisition and LTR of a distributed shuttle-box avoidance depend on the difficulty of the task.

Facilitation of shuttle-box avoidance by the platform method: temporal effects.

Two experiments were carried out in order to 1) replicate a previous finding according to which the treatment on large platforms (commonly used as control for the stress induced by smaller paradoxical sleep deprivation platforms) can facilitate the acquisition and long-term retention (LTR) of a distributed shuttle-box avoidance in rats, and 2) further examine the temporal conditions in which that facilitation can be observed. The results showed that an immediate posttraining treatment lasting 6 hours induced a significant improvement of acquisition both when applied in the light (8 a.m.) and in the dark cycle (8 p.m.), while the LTR (10 and 31 days) seemed to be better preserved when the treatment was applied during the dark cycle. A shorter treatment (3 h) had no effect upon shuttle-box avoidance, regardless of whether it was applied in the dark or in the light cycle and whether it was immediate or delayed for 3 h. In summary, under certain temporal conditions, a posttraining immediate treatment on large platforms can facilitate the acquisition and/or the LTR of shuttle-box avoidance. Stress hormones and/or the enhancement of CNS arousal are suggested to be some of the mechanisms operating in this facilitatory effect.

Correlations between paradoxical sleep and shuttle-box conditioning in rats.

Eighteen male Wistar rats were given one daily two-way active avoidance conditioning session followed immediately by 5 hr of sleep recording, for 5 consecutive days. The group of rats that achieved 80% or greater avoidance in some of the 5 training sessions showed significant linear increases of paradoxical sleep (PS), compared with baseline levels, throughout the successive conditioning sessions. Furthermore, (a) the group of rats showing PS increases (more than 1 SD above baseline) after some of the training sessions achieved a significantly higher final number of avoidances than the remaining animals: (b) a high and positive correlation was observed between avoidance increases in the 3rd conditioning session and previous PS; and (c) maximum increases in correct performance often occurred following high PS increases. It is concluded that PS increases facilitate the consolidation of learning.

Improvement of shuttle-box learning with pre- and post-trial intracranial self-stimulation in rats.

The effects of intracranial self-stimulation (ICSS) in the lateral hypothalamus upon the acquisition and long-term retention (LTR) of shuttle box avoidance conditioning were studied in Wistar rats. Two groups of subjects learned the avoidance task in 5 daily training sessions and were allowed to self-stimulate either before (Pre-ICSS group), or after (Post-ICSS group) each training session. A control group received training but no ICSS. Ten days following the last training session, LTR of the task was determined in one avoidance session without ICSS. A fourth group was added post-hoc which was allowed to self-stimulate before the training sessions as well as before the LTR test. Both the Post-ICSS and Pre-ICSS groups improved in acquisition of the learned response over the successive training sessions, as compared with Controls. In the LTR test, the animals of the Post-ICSS group maintained the response level achieved in the last acquisition session. In contrast, the subjects of the Pre-ICSS group showed a significant decrease of the same response, unless they were given ICSS treatment prior to the LTR test. This may indicate a 'state-dependent learning' effect being responsible for the decrease in the LTR observed in Pre-ICSS group. Because both pre- and post-training ICSS treatments improved the acquisition and the LTR of the learned response, it is suggested that the contingency of the treatment with training (that is, ICSS treatment immediately after the training sessions) is not a necessary condition to facilitate the acquisition and the consolidation of two-way active avoidance learning.