Perceived tiredness and heart rate variability in relation to overload during a field hockey World Cup.

The aim of the study was to examine the utility of perceived tiredness to predict cardiac autonomic response to overload among field hockey players during the 2006 World Cup. The French Society for Sports Medicine (SFMS) questionnaire was administered at the start of the Cup to evaluate perception of tiredness. Autonomic function was assessed nine days later at the semifinal match by time and frequency domain analysis of heart rate variability. An anxiety questionnaire was administered so that the effect of precompetitive anxiety on heart rate variability could be controlled. Results showed a negative correlation between perceived tiredness scores and time domain indexes, and a positive correlation of perceived tiredness scores and the high frequency component ratio (LF/HF ratio) of heart rate variability. Anxiety did not influence the precompetitive cardiac response despite somatic anxiety's correlation with sympathetic response (LF/HF ratio) and tiredness scores. Perceived tiredness predicted the autonomic cardiac response to competitive overload. Thus, the perceived tiredness assessment would be a good early marker of fatigue and overload states during competition.

Orienting of attention with eye and arrow cues and the effect of overtraining.

In contrast to the classical distinction between a controlled orienting of attention induced by central cues and an automatic capture induced by peripheral cues, recent studies suggest that central cues, such as eyes and arrows, may trigger a reflexive-like attentional shift. Yet, it is not clear if the attention shifts induced by these two cues are similar or if they differ in some important aspect. To answer this question, in Experiment 1 we directly compared eye and arrow cues in a counter-predictive paradigm while in Experiment 2 we compared the above cues with a different symbolic cue. Finally, in Experiment 3 we tested the role of over-learned associations in cueing effects. The results provide evidence that eyes and arrows induce identical behavioural effects. Moreover, they show that over-learned associations between spatially neutral symbols and the cued location play an important role in yielding early attentional effects.

Association between learning capabilities and practice-related activation changes in schizophrenia.

The present functional magnetic resonance imaging study investigated the neural correlates of practice-associated activation changes in patients with schizophrenia and their association with symptom severity. A group of patients (n = 24) were divided into more successful and less successful learners and were asked to perform a verbal overlearning task in the scanner. We found that both patient groups profited from practice, showing significant decreases in mean response times as well as significant learning-related decreases in cerebral activation. Direct comparison between groups yielded a relative hyperactivation in the group of the less successful learners at the beginning of practice, which showed a reduction with increasing practice. This was reflected by relatively stronger signal decreases in a predominantly fronto-parieto-cerebellar network. In the group of less successful learners, there was a negative correlation between general symptom scores and learning-related signal decreases in a task-relevant network involving cerebellar, inferior and middle frontal (BA 45/47, 46), superior parietal (BA 31), and superior temporal (BA 39) regions. Present data indicate that hyperactivity under high task demands might serve to identify those patients with less potential to profit from practice. However, at least in the context of moderate- to low-working memory demands, this activation abnormality seems to constitute a state rather than a trait characteristic, which patients manage to reduce by successful short-term learning. The findings also suggest that successful learners can better compensate potentially interfering effects exerted by disorder-related psychopathology.

Confabulation in healthy aging is related to interference of overlearned, semantically similar information on episodic memory recall.

Normal aging is characterized by reduced performance on tasks of long-term memory. Older adults (OA) not only show reduced performance on tasks of recall and recognition memory, but also, compared to young adults (YA), are more vulnerable to memory distortions. In this study we describe the performance of a group of OA and a group of YA on the recall of three different types of story: a previously unknown story, a well-known fairy tale (Sleeping Beauty), and a modified well-known fairy tale (Little Red Riding Hood is not eaten by the wolf). The aim of our study was to test the hypothesis that in OA strongly represented, overlearned information interferes with episodic recall-that is, the retrieval of specific, unique past episodes. OA produced significantly more confabulations than YA and in particular in the recall of the modified fairy tale. Our findings indicate that the interference of strongly represented, overlearned information in episodic memory recall is implicated in the production of confabulations in OA. This effect is particularly prominent when the to-be remembered episodic information shows strong semantic similarities with preexisting, overlearned information.

The objectification of overlearned sequences: a new view of spatial sequence synesthesia.

In the phenomenon of spatial sequence synesthesia (SSS), subjects can articulate explicit spatial locations for sequences such as numbers, letters, weekdays, months, years, and other overlearned series. Similarly, abstract sequences can take on implicit spatial representations in non-synesthetes, as evidenced by the spatial numerical association of response codes (SNARC) effect. An open question is whether the two findings represent different degrees of the same condition, or different conditions. To address this, we developed computer programs to quantify three-dimensional (3D) month-form coordinates in 571 self-reported spatial sequence synesthetes; this approach opens the door for the first time to quantified large-scale analysis. First, despite the common assumption that month-forms tend to be elliptical, we find this to be true in only a minority of cases. Second, we find that 27% of month forms are in the shape of lines, consistent with the assumed shape of implicit spatial forms in the SNARC effect. Next, we find that the majority of month forms are biased in a left-to-right direction, also consistent with the directional bias in the SNARC effect (in Western speakers). Collectively, these findings support the possibility that SSS is directly related to the sequence representations in non-synesthetes. While the search for neural correlates has concentrated on areas in the parietal lobe involved in numeric manipulation and coordinate systems, we propose that the basis of this synesthesia may be the close proximity of temporal lobe regions implicated in sequence coding and visual object representation.

Intensive practice of a cognitive task is associated with enhanced functional integration in schizophrenia.

BACKGROUND: There is increasing evidence that the frequently reported working memory impairments in schizophrenia might be partly due to an alteration in the functional connectivity between task-relevant areas. However, little is known about the functional connectivity patterns in schizophrenia patients during learning processes. In a previous study, Koch et al. [Neuroscience (2007) 146, 1474-1483] have demonstrated stronger exponential activation decreases in schizophrenia patients during overlearning of short-term memory material. The question arises whether these differential temporal patterns of activation in schizophrenia patients and controls are going along with changes in task-related functional connectivity. METHOD: Therefore, in the current study, 13 patients with schizophrenia and 13 controls were studied while performing a short-term memory task associated with increasing overlearning of verbal stimulus material. Functional connectivity was investigated by analyses of psychophysiological interactions (PPI). RESULTS: Results revealed significant task-related modulation of functional connectivity between the left dorsolateral prefrontal cortex (DLPFC) and a network including the right DLPFC, left ventrolateral prefrontal cortex, premotor cortex, right inferior parietal cortex, left and right cerebellum as well as the left occipital lobe in patients during the course of overlearning and practice. No significant PPI results were detectable in controls. CONCLUSIONS: Activation changes with practice were associated with high functional connectivity between task-relevant areas in schizophrenia patients. This could be interpreted as a compensatory resource allocation and network integration in the context of cortical inefficiency and may be a specific neurophysiological signature underlying the pathophysiology of schizophrenia.

Intrusions in story recall: when over-learned information interferes with episodic memory recall. Evidence from Alzheimer's disease.

Patients with Alzheimer's disease (AD) suffer from distortions of memory. Among such distortions, intrusions in memory tests are frequently observed. In this study we describe the performance of a group of mild AD patients and a group of normal controls on the recall of three different types of stories: a previously unknown story, a well-known fairy-tale (Cinderella), and a modified well-known fairy-tale (Little Red Riding Hood is not eaten by the wolf). The aim of our study was to test the hypothesis that in patients who tend to produce intrusions, over-learned information interferes with episodic recall, i.e., the retrieval of specific, unique past episodes. AD patients produced significantly more intrusions in the recall of the modified fairy-tale compared to the recall of the two other stories. Intrusions in the recall of the modified fairy-tale always consisted of elements of the original version of the story. We suggest that in AD patients intrusions may be traced back to the interference of strongly represented, over-learned information in episodic memory recall.

Cerebral changes during performance of overlearned arbitrary visuomotor associations.

The posterior parietal cortex (PPC) is known to be involved in the control of automatic movements that are spatially guided, such as grasping an apple. We considered whether the PPC might also contribute to the performance of visuomotor associations in which stimuli and responses are linked arbitrarily, such as producing a certain sound for a typographical character when reading aloud or pressing pedals according to the color of a traffic light when driving a motor vehicle. The PPC does not appear to be necessary for learning new arbitrary visuomotor associations, but with extensive training, the PPC can encode nonspatial sensory features of task-relevant cues. Accordingly, we have tested whether the contributions of the PPC might become apparent once arbitrary sensorimotor mappings are overlearned. We have used functional magnetic resonance imaging to measure cerebral activity while subjects were learning novel arbitrary visuomotor associations, overlearning known mappings, or attempting to learn frequently changing novel mappings. To capture the dynamic features of cerebral activity related to the learning process, we have compared time-varying modulations of activity between conditions rather than average (steady-state) responses. Frontal, striatal, and intraparietal regions showed decreasing or stable activity when subjects learned or attempted to learn novel associations, respectively. Importantly, the same frontal, striatal, and intraparietal regions showed time-dependent increases in activity over time as the mappings become overlearned, i.e., despite time-invariant behavioral responses. The automaticity of these mappings predicted the degree of intraparietal changes, indicating that the contribution of the PPC might be related to a particular stage of the overlearning process. We suggest that, as the visuomotor mappings become robust to interference, the PPC may convey relevant sensory information toward the motor cortex. More generally, our findings illustrate how rich cerebral dynamics can underlie stable behavior.

Content-specific activation during associative long-term memory retrieval.

We tested whether visual stimulus material that is assumed to be processed in different cortical networks during perception (i.e., faces and spatial positions) is also topographically dissociable during long-term memory recall. With an extensive overlearning procedure, 12 participants learned paired associates of words and faces and words and spatial positions. Each word was combined with either one or two positions or one or two faces. fMRI was recorded several days later during a cued recall test, in which two words were presented and the participants had to decide whether these were linked to each other via a common mediator, i.e., a face or a position. This paradigm enforces retrieval from long-term memory without confounding recall with perceptual processes. A network of cortical areas was found to be differently activated during recall of positions and faces, including regions along the dorsal and ventral visual pathways, such as the parietal and precentral cortex for positions and the left prefrontal, temporal (including fusiform gyrus) and posterior cingulate cortex for faces. In a subset of these areas, the BOLD response was found to increase monotonically with the number of the to-be-re-activated associations. These results show that material-specific cortical networks are systematically activated during long-term memory retrieval that overlap with areas also activated by positions and faces during perceptual and working memory tasks.

The inhibition of imitative and overlearned responses: a functional double dissociation.

Neuropsychological research has established that the inhibition of dominant response tendencies is a function of the prefrontal cortex. These inhibitory mechanisms are tested using tasks like the Stroop task, in which the prepotency of the dominant response is based on a learned relationship of stimulus and response. However, it has also been reported that patients with prefrontal lesions may have problems inhibiting imitative responses. The question arises of whether the inhibition of overlearned and imitative responses entails the same or different functional mechanisms and cortical networks. In a recent neuropsychological study with prefrontal patients we found first evidence for such a dissociation. The present fMRI study further investigated this question by directly comparing brain activity in the inhibition of overlearned and imitative response tendencies. It emerges that response inhibition in the two tasks involves different neural networks. While the inhibition of overlearned responses requires a fronto-parietal network involved in interference control and task management, the inhibition of imitative responses involves cortical areas that are required to distinguish between self-generated and externally triggered motor representations. The only frontal brain area that showed an overlap was located in the right inferior frontal gyrus and is probably related to the generation of the stop signal.

fMRI of healthy older adults during Stroop interference.

The Stroop interference effect, caused by difficulty inhibiting overlearned word reading, is often more pronounced in older adults. This has been proposed to be due to declines in inhibitory control and frontal lobe functions with aging. Initial neuroimaging studies of inhibitory control show that older adults have enhanced activation in multiple frontal areas, particularly in inferior frontal gyrus, indicative of recruitment to aid with performance of the task. The current study compared 13 younger and 13 older adults, all healthy and well educated, who completed a Stroop test during functional magnetic resonance imaging. Younger adults were more accurate across conditions, and both groups were slower and less accurate during the interference condition. The groups exhibited comparable activation regions, but older adults exhibited greater activation in numerous frontal areas, including the left inferior frontal gyrus. The results support the recruitment construct and suggest, along with previous research, that the inferior frontal gyrus is important for successful inhibition.

Partial reinforcement across trials impairs escape performance but spares place learning in the water maze.

We studied the effects of partial reinforcement on escape performance and place learning in the water maze. Rats given 50% reinforcement across trials (i.e. the escape platform was present only on odd trials) were compared to controls given 100% reinforcement (platform present on all trials). Control groups either received 8 or 4 trials per day, which was equal to either the total number of trials (100%-8) or reinforced escapes (100%-4) of the 50% group. Analysis of escape performance (latency) revealed that the 50% group was impaired relative to the 100%-8 group, but not the 100%-4 group, during the first 5 days of acquisition. The 50% group was impaired relative to both control groups on days 6-10 of overtraining. However, analyses of within-trial behavior (target annulus preference and thigmotaxis) on nonreinforced trials suggest that the 50% group did learn the location of the hidden platform (place information), in addition to a wall-based thigmotactic response. By dividing the 60s nonreinforced trials into three 20-s time bins, we were able to detect a significant preference for the target annulus early in the trial (bin 1 of trial 40 and bins 1-2 of trial 80). Further, there was a significant increase in time spent in the periphery of the pool, near the wall, in the last time bin of trial 40. Because the platform was in the middle zone, this behavior competed with a place response. We conclude that across-trial partial reinforcement procedures may promote response competition and mask evidence of place learning in addition to weakening escape performance late in training.

Effect of stimulus intensity and number of treatments on ECS-related seizure duration and retrograde amnesia in rats.

BACKGROUND: Animal models are frequently used to generate and test hypotheses about amnesia resulting from electroconvulsive therapy (ECT). Although many predictors of ECT-induced amnesia are known, their relative effects have been inadequately researched in the context of the animal models. OBJECTIVE: We sought to determine the relative retrograde amnestic effects of electroconvulsive shock (ECS) stimulus intensity (dose) and number on strong memories in rats. We also sought to identify dose-dependent ceiling amnestic effects, if any. METHODS: Adult rats (n = 144) were overtrained in a passive avoidance task using a step down apparatus. The rats were then randomized in a factorial design to receive one, two, or three once-daily bilateral ECS at 0-mC (sham ECS), 30-mC, 60-mC, 120-mC, or 180-mC doses. Recall of the pre-ECS training was assessed 1 day after the last ECS. RESULTS: Retrograde amnesia was observed only in rats that received 3 ECS; dose-dependent amnestic effects did not emerge. Higher stimulus intensity was associated with a small (13%) but significant increase in motor seizure duration, but only at the first ECS; stimulus intensity did not influence the attenuation of seizure duration across repeated occasions of ECS. CONCLUSION: With bilateral ECS, the number of ECSs administered is a more important variable than the ECS dose in weakening a strong, recently acquired, noxious memory; this finding may have important clinical implications. Higher stimulus intensity marginally increases motor seizure duration at the first ECS but does not influence the decrease in seizure duration across repeated ECSs.

Differential activation of monkey striatal neurons in the early and late stages of procedural learning.

The basal ganglia is a key structure for procedural learning. To examine in what aspects of procedural learning the basal ganglia participate, we recorded from striatal neurons (phasically active neurons) in monkeys while the animals were performing a sequential button press task (the 2 x 5 task) and compared the neuronal activity between two conditions: (1) while learning new sequences and (2) while executing overlearned sequences. Among 147 neurons recorded in two monkeys, 45 neurons were activated preferentially for new sequences (new-preferring neurons), 34 for overlearned sequences (learned-preferring neurons), and 68 were activated non-selectively (non-selective neurons). New-preferring neurons were more abundant in the "association" region [association striatum (AS); caudate nucleus and rostral putamen anterior to the anterior commissure], while the learned-preferring neurons were more abundant in the "sensorimotor" region [sensorimotor striatum (SM); putamen posterior to the anterior commissure]. In addition to the learning dependency, the AS and SM neurons were activated in different task periods: many AS neurons were activated during the delay period, while the SM neurons were more activated with reaching and button presses. These data, together with the data from our previous blockade study, suggest that the "association" and "sensorimotor" regions of the basal ganglia contribute preferentially to the early and late stages of procedural learning, respectively.

Alleviation of overtraining reversal effect by transient inactivation of the dorsal striatum.

In this study, we investigated the role of the dorsal striatum in the acquisition and the use (retrieval) of a specific learning developed during overtraining. The paradigm was such that rats had to respond differentially to two signals in order to obtain food or to avoid an electrical footshock. Overtraining was aimed at eliciting a facilitative effect on discrimination reversal as compared to simply trained rats. In this way, transient inactivation of the dorsal striatum by lidocaine enabled us to investigate, separately, the role of this structure during overtraining and reversal. The data show that inactivating the dorsal striatum before each reversal session prevented the overtraining reversal effect observed in control rats. Moreover, inactivation of the dorsal striatum during overtraining had no effect on the level of discriminative performance just as it did not affect the subsequent facilitative effect on reversal. These results show that even though the striatum might normally be part of a routine automatic system, clearly its contribution is not essential. Indeed, despite inactivation of the striatum in overtrained rats, their ability to develop an efficient selection process that can be used during reversal was observed. However, the integrity of the striatum became essential in order to mediate the modification of behaviour when this behavioural routine formed during overtraining had to be modified during reversal.

Is posttraumatic stress disorder an overlearned survival response? An evolutionary-learning hypothesis.

Contemporary learning theories of posttraumatic stress disorder (PTSD) provide an explanation for the phobic avoidant features but do not account fully for the intrusive phenomena that are so characteristic of the disorder. This article hypothesizes that a primitive learning center in the limbic system rehearses traumatic memories immediately following exposure to trauma, thus inducing durable memories of the sources of novel threat. It is postulated that the mechanism developed during early evolution when, in the absence of cognitive mechanisms, automatic learning following single exposure to novel threat would have conferred survival value on the species. With evolution of the brain, a second cortical pathway developed for the cognitive processing of trauma memories. It is possible that synchrony between the two phylogentically distinct pathways may be lost in vulnerable individuals under conditions of extreme stress resulting in failure of cortical inhibition of limbic trauma rehearsal mechanisms. A mismatch between archaic biological mechanisms and novel cues in the modern environment also may play a role in triggering traumatic memories and associated fight and flight reactions. The intrusive phenomena of PTSD thus may reflect an "overlearned survival response" in those in whom the putative limbic rehearsal mechanism evades cortical control. The heuristic value and limitations of such an evolutionary-learning theory are discussed.

Timed active avoidance learning in lurcher mutant mice.

Lurcher mutant mice (+/Lc) which exhibit a massive loss of neurons in the cerebellar cortex and in the inferior olivary nuclei were subjected to an active avoidance learning task; the animals' avoidance response must occur within a small time window after a short or a long delay. The control mice needed a mean of 8.3 sessions of 10 trials (short delay group) and of 11.8 sessions (long delay group) and showed good retention after a 24 h interval. When subjected to the same number of sessions, the +/Lc mice were unable to learn the timing task. However, a subgroup of lurcher mutants was able to learn after a high number of sessions (25.4 sessions as a mean). There was no intergroup difference in the standard version of one-way active avoidance. These results indicate that the cerebellar cortex is involved in time processing during active avoidance. The cerebellum may be part of a loop including the cerebral cortex known to be involved in time perception. An alternative explanation is that the cerebellar mutant animals had persevering tendencies acquired during performance of the one-way avoidance task.

The nomadic engram: overtraining eliminates the impairment of discriminative avoidance behavior produced by limbic thalamic lesions.

Combined lesions of the medial dorsal and anterior thalamic nuclei severely impair the acquisition of discriminative avoidance behavior, wherein rabbits learn to prevent foot-shock by stepping after a tone conditional stimulus (CS+), and they learn to ignore a different tone (CS-) that does not signal foot-shock. Neurons in these thalamic nuclei exhibit training-induced firing pattern changes during behavioral acquisition to asymptotic performance levels. However, the changes decline in magnitude during the course of post-asymptotic training (overtraining), suggesting a declining participation of the thalamic neurons in task mediation. In order to test this hypothesis, electrolytic or sham limbic thalamic lesions were induced either immediately after asymptotic performance was reached, or after the administration of training to asymptote and ten additional overtraining sessions. Retention after the lesions was assessed using an extinction procedure (CS presentation without foot-shock) followed by re-acquisition. Rabbits given lesions after criterion attainment exhibited a significant retention deficit during both the extinction and re-acquisition tests. However, no significant retention deficit was found in rabbits given 10 days of overtraining prior to the lesions. These results support the prediction derived from the neuronal data, of a time-limited involvement of limbic thalamic neurons in mediation of discriminative avoidance behavior.

[The relearning time of rats in a radial maze elicited by the revolving alteration of extra-maze markers]. / Vremia pereobucheniia krys v radial'nom labirinte, vyzvannogo krugovym izmeneniem vnelabirintnykh markerov.

A new approach was applied to evaluation the errors in the course of learning of rats in 12-arm radial maze (RM). The number of repeated erroneous visits of the last six arms ("late errors") decreased only after a decrease in the number of repeated erroneous visits of the first six arms ("early errors"). This points to insufficiency of using the common index of the mean error for evaluating learning ability in the RM. Change in the character of errors in the operative and space memory was studied in the RM-conditioned rats after disruption of the relations between the intra- and extra-maze markers. This disruption was reached by rotation of the RM by 180 degrees after rat's visiting of 5 arms during its stay in the 6th one. It was found out that rats were able to recognize the changes in the extra-maze markers caused by the RM turn and to relearn within 4-5 days.