Memory processes in children with learning disabilities: evidence for deficient rehearsal.
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The effects of hippocampectomy on performance by rats of a running recognition task using long lists of non-spatial items.
Unoperated rats, or rats with cortical control lesions or hippocampal aspiration lesions, were trained on a non-spatial delayed non-matching-to-sample task. Once the non-matching rule had been learned, the task was modified so as to assess list memory, with list lengths of up to 32 items. Hippocampectomy induced a significant drop in choice accuracy, that was independent of list length; nonetheless, hippocampectomised rats still performed at better than chance levels. The cortical control lesion appeared to induce an intermediate (though generally non-significant) deficit. It was concluded that hippocampectomy leaves rats still capable of choosing with considerable accuracy on non-spatial working memory tasks that use trial-unique or 'pseudo-trial-unique' stimuli, even under experimental conditions in which a heavy memory load is imposed.
Animals↗
Memory impairment and auditory evoked potential gating deficit in schizophrenia.
Impaired sensory gating and memory function were reported in a study of 10 schizophrenic patients and 10 age- and sex-matched normal subjects. The P50 component of the auditory evoked potential was used as an index of gating. Explicit memory was tested with the Wechsler Memory Scale and implicit memory by artificial grammar learning. The schizophrenic patients showed deficits in both verbal paired associate and visual reproduction tasks. They demonstrated impaired implicit learning in color patterns but not letter strings. They also showed impaired P50 sensory gating. Three-dimensional brain mapping revealed a differential distribution of brain potentials in the processing of S1 and S2 at either P50 or N100 in both groups. However, the group difference was not statistically confirmed. In the controls, both implicit letter-string learning and explicit verbal paired associates were positively correlated with N100 gating, suggesting an association of the early attentive component with lexicons. In the schizophrenic patients, color-pattern implicit learning was positively correlated with P50 gating. The modality-specific impairment of implicit learning in schizophrenia may reflect a failure of adaptive filtering on the flooding input from color patterns.
Adult↗
Developmental 3,4-methylenedioxymethamphetamine (MDMA) impairs sequential and spatial but not cued learning independent of growth, litter effects or injection stress.
Previously, we have shown that rats administered MDMA from postnatal (P) days 11-20 had reductions in body weight during the period of treatment and as adults they had deficits in sequential and spatial learning and memory. In the present study, to control for weight reductions, we used litters with double the number of offspring to induce growth restriction comparable to that of standard size litters treated with MDMA. Litters were treated twice daily from P11 to 20 with vehicle or MDMA (20 mg/kg) or only weighed. Males, but not females, exposed to MDMA had longer latencies and more errors in the Cincinnati water maze compared to males of the other treatments. In the Morris water maze (210 cm pool, 10x10 cm platform), the MDMA animals were impaired relative to all other treatments during acquisition. Only the MDMA females showed deficits when the platform was shifted to a new location, however, both MDMA males and females were impaired when the location of the platform was again shifted and a reduced platform (5x5 cm) used. No differences were observed in the ability to swim a straight channel, locate a platform with a cue, or the endocrine response to forced swim among the treatment groups. No differences were seen between animals injected with saline and those only weighed. The data suggest that factors, such as growth retardation, multiple injections, or the composition of the litter, do not affect the development of learning and memory impairments resulting from P11 to 20 MDMA exposure. The large litter approach offers a novel method to control for undernutrition during the preweaning period in rodents.
3,4-Methylenedioxyamphetamine↗
A disturbance in the conceptual organization of actions in patients with ideational apraxia.
Patients with ideational apraxia (i.a.) performed significantly worse than patients without i.a. in a task where they had to arrange pictures in correct order illustrating actions requiring the use of various objects. There was no influence of severity of aphasia nor presence or severity of ideomotor apraxia. In two similar pictorial tasks, where consecutive stages of common events are illustrated, which, however, did not include manipulation of objects, there was no difference in performance of patients with and without i.a. It is concluded that i.a. is a disturbance in the conceptual organization of actions.
Adult↗
Memory for spatial location as a function of temporal lag in rats: role of hippocampus and medial prefrontal cortex.
Rats with medial prefrontal cortex, hippocampus, or cortical control lesions were tested on an eight-arm radial maze task, in order to examine memory for the temporal order of spatial locations as a function of temporal lag. During the study phase of each trial, rats were allowed to visit each of eight arms once in an order that was randomly selected for that trial. The test phase required the rats to choose which of two arms occurred earlier in the sequence of arms visited during the study phase. The arms selected as test arms varied according to temporal lag (0-6) or the number of arms that occurred between the two test arms in the study phase. The control rats performed at chance at a temporal lag of zero, but their performance was above chance for the remaining lags, improving after the temporal lag exceeded zero. The hippocampal-lesioned rats showed a marked deficit, performing at chance for all lags, with some savings for those items occurring at the end of the list. The medial prefrontal cortex-lesioned rats showed a less severe deficit. The results of these data support the notion that both the hippocampus and the medial prefrontal cortex play significant roles in memory for the temporal order of spatial locations.
Animals↗
Temporal contextual cuing of visual attention.
Previous research has shown how spatial attention is guided to a target location, but little is understood about how attention is allocated to an event in time. The authors introduce a paradigm to manipulate the sequential structure of visual events independent of responses. They asked whether this temporal context could be implicitly learned and used to guide attention to a relative point in time or location, or both, in space. Experiments show that sequentially structured event durations, event identities, and spatiotemporal event sequences can guide attention to a point in time as well as to a target event's identity and location. Cuing was found to rely heavily on the element immediately preceding the target, although cuing from earlier items also was evident. Learning was implicit in all cases. These results show that the sequential structure of the visual world plays an important role in guiding visual attention to target events.
Adult↗
Cognitive consequences of congenital deafness.
Comparing congenitally deaf children with hearing children on a variety of information processing tasks provides a natural test of the developmental consequences accompanying the long term loss of a particular sensory input. In this experiment, two sequential and two spatial tasks were used to evaluate the way deaf and hearing individuals process these different types of information. When deaf students were asked to recall the order of a string of lights, they performed as well as hearing students. Deaf students were at a significant disadvantage, however, when processing sequentially presented digits. Deaf students performed as well as hearing students on two complex, standardized spatial tasks. The loss of a major sensory modality had minimal effect on three of the four tasks investigated in the present study. Explanations for the single task with a performance differential are considered.
Adolescent↗
Implicit learning of a motor skill after mild and moderate stroke.
OBJECTIVE: To determine if adults in the subacute phase post moderate or mild stroke could learn a motor task under implicit practice conditions. DESIGN: Non-randomized, between-group design. SETTING: Subjects' homes. SUBJECTS: Sample of convenience of 15 adults with moderate stroke, 22 adults with mild stroke, and 32 age-matched controls. Stroke severity was determined using the Orpington Prognostic Scale. INTERVENTION: Practice of movements to target switches in two conditions, a repeated series and a random series. Practice was organized into a single session of six blocks of 80 trials such that blocks 1 and 2 were the random series, blocks 3 and 4 the repeated series, block 5 the random series, and block 6 the repeated series. Explicit knowledge of the two conditions was not provided. MAIN MEASURES: The mean response time and the coefficient of variation were calculated for each block for each group. RESULTS: Regardless of group, participants had a slower response time when practice was unexpectedly switched from the repeated to random condition. The response time and coefficient of variation for those with moderate stroke were persistently greater than those with mild stroke and controls, who were not different from each other. CONCLUSIONS: Implicit motor learning is preserved in adults with moderate stroke and may be a viable strategy for teaching motor skills in rehabilitation. The clinician should be aware that subjects with moderate stroke, even when performing with the less affected upper extremity, have significantly slower and more variable movements than those with mild stroke and controls.
Aged↗
Reproduction memory of two-event sequences in pigeons.
Six pigeons were trained to reproduce two-event sequences in an experiment that employed a discrete-trial procedure that required subjects to peck one of four possible sample sequences (left-left, left-right, right-right, right-left) signaled on a given trial by the successive illumination of response keys. Following a retention interval (0.1 to 30 seconds), a reinforcer was delivered if a subject reproduced the prior sample sequence during a test condition in which both left and right keys were illuminated. The pigeons readily reproduced the orders in which they had just seen and pecked two illuminated keys. Reproduction accuracy declined as the retention interval was increased. Homogeneous sequences (left-left, right-right) were reproduced with greater accuracy than heterogeneous sequences.
Animals↗
A corpus callosal deficit in sequential analysis by schizophrenics.
This preliminary study evaluated interhemispheric (i.e., corpus callosal) information processing by chronic schizophrenic and normal subjects. In right-handed normals the left hemisphere has been reported to be superior in temporal sequential analysis. Consequently temporal information presented to the right hemisphere requires time to cross to the left hemisphere for analysis. Measurement of hemispheric laterality and corpus callosal transfer time were evaluated by a two-pulse temporal discrimination task. Two dot stimuli were presented with decreasing temporal separation during bilateral and unilateral conditions. Subjects were required to judge perceived simultaneity and nonsimultaneity of dot onset. The results indicate that left hemisphere function in chronic schizophrenic and normal controls is superior to the right hemisphere in temporal analysis. Corpus callosal transfer time was significantly slower for chronic schizophrenics than for normal controls.
Adult↗
Cognitive self-consciousness, implicit learning and obsessive-compulsive disorder.
The negative appraisal of commonly experienced intrusive thoughts is posited to play an important role in obsessive-compulsive disorder (OCD), although why some people focus on thought experiences and have difficulties dismissing intrusions is not well understood. To elucidate how intrusive thoughts might become obsessional problems, relations between thought-focused attention (cognitive self-consciousness; CSC), implicit sequence learning and OCD were evaluated in individuals with OCD (n=43) and in a nonclinical comparison group (n=41). Impaired performance on a serial reaction time test, but enhanced recognition of the embedded stimulus pattern, was predicted for the OCD group based on hypothesized nonconscious processing differences. Predicted differences were found and CSC score predicted reaction time and pattern recognition. CSC might be a consequence of conscious processing gating problems that increase thought salience and the likelihood of the negative appraisal of intrusive thoughts. Implications for theory and treatment are discussed.
Adolescent↗
Hemispheric differences in split-brain monkeys learning sequential comparisons.
Twelve split-brain rhesus monkeys were tested for differences in the abilities of their two cerebral hemispheres to learn discriminations based on the comparison of sequentially-presented visual stimuli. Overall there was no generalized advantage for either the left or right hemisphere. There was, however, a significant correlation between each monkey's handedness and the hemisphere that learned more readily; the more proficient hemisphere tended to be contralateral to the preoperatively preferred hand. This result raises the possibility that handedness in monkeys may be more closely related to cognitive processing than is usually believed.
Animals↗
Behavioral and functional MRI study of attention shift in human verbal working memory.
The tripartite model of memory proposed the requirement of attentional switching when accessing different items in working memory [J. Exp. Psychol. Learn. Mem. Cogn. 27 (2001) 817]. This internal focus of attention is limited to just one item and the switching process is time-consuming [Mem. Cogn. 26 (1998) 263]. In the current study, given a three-digit list stored in working memory, we found that it took longer to shift attention in the direction of "Upstream" than "Downstream", and that each shift was a "single step" process. To investigate the neural basis of this type of attention switching, we performed a functional MRI study. The results revealed that at least three important brain areas are involved, including the left dorsal lateral prefrontal cortex, the cingulate gyrus, and the medial occipital cortex. These areas all showed greater activation in the attention shift condition compared to control conditions of no (or decreased) attention shift requirements. In addition, the hemodynamic activities in these areas are highly correlated, suggesting a strong functional connectivity between them. Taken together with evidence from several recent investigations, our results suggest that these areas each play an important and specific role in collaboratively supporting the function of attention shift in working memory.
Adolescent↗
Impaired temporal context memory on anterograde but not retrograde tests in the absence of frontal pathology.
This study examined the memory performance of patient RK who developed substantial memory impairments due to a hypothalamic glioma but in the absence of any evidence of frontal disturbance. RK was evaluated on both tests of anterograde and retrograde memory for temporal context. In the first experiment he exhibited marked deficits on a list discrimination task even when recognition performance was well within control range. Experiment 2 confirmed this disproportionate impairment of temporal order memory and showed that RK's list discrimination deficit was as severe as that found in alcoholic Wernicke-Korsakoff Syndrome patients. Experiment 3 showed that RK's temporal discrimination deficit was not a general deficit in discrimination because he performed normally on a spatial discrimination test of comparable difficulty to the temporal task. Experiment 4 examined RK's memory for deceased famous people and his ability to indicate the half decade in which they died. RK's performance was indistinguishable from controls whereas WKS patients were extremely impaired. This study adds to the view that frontal damage is not a necessary condition for impairment on anterograde measures of temporal context memory. However, further evidence from this study indicates that temporal judgments about pre-existing memories may depend on intact frontal lobe functioning.
Adult↗
Dividing attention within and between hemispheres: testing a multiple resources approach to limited-capacity information processing.
Two experiments tested the limiting case of a multiple resources approach to resource allocation in information processing. In this framework, the left and right hemispheres are assumed to have separate, limited-capacity pools of undifferentiated resources that are not mutually accessible, so that tasks can overlap in their demand for these resources either completely, partially, or not at all. We tested all three degrees of overlap in demand for left hemisphere supplies, using dual-task methodology in which subjects were induced to pay different amounts of attention to each task. Experiment 1 compared complete and partial overlap by combining a verbal memory load with a task in which subjects named nonsense syllables briefly presented to either the left or right visual field (LVF and RVF, respectively). Experiment 2 compared complete versus no overlap by using the same verbal memory load combined with a laterally presented same-different judgment task that did not require a spoken response. Decrements from single-task performance were always more severe when the visual field task stimulus was presented to the RVF. Further, subjects in Experiment 1 were able to trade performance between tasks on both LVF and RVF trials because there was always at least some overlap in left hemisphere demand. In Experiment 2, performance trade-offs were observed on RVF (complete overlap) trials, but not on LVF trials, where no overlap in demand existed. These results contradict a single-capacity model, but they support the idea that the hemispheres' resource supplies are independent and have implications for both cerebral specialization and divided attention issues.
Attention↗
Remembering and constructing an order.
The purpose of this study was to determine whether children who could recognize a linear order would be able to use this recognition to answer new questions about the linear order. Three-, 4-, 5-, and 6-year-old children were trained to choose a series over a nonseries, a series over a series ordered in the opposite direction, or one nonseries over another nonseries. They were also given a standard seriation task. Children could recognize a series before being able to construct one, but recognition of a series was not correlated with construction of a series. Although children did not use the linear order to construct a series, they could use it to make choices between two similar stimuli, only one of which contained a feature identical to the linear order. The comparison between seriation and recognition of one nonseries over another revealed that performance on these two tasks was correlated and that one common feature between them was systematicity, which occurred either in searching for relationships or constructing them.
Attention↗
Regional brain activation during concurrent implicit and explicit sequence learning.
We used event-related fMRI to identify the brain regions engaged during explicit and implicit sequence learning (ESL and ISL, respectively). Twenty-four subjects performed a concurrent ESL and ISL task. Behavior showed learning in both conditions. Prefrontal (PFC), striatal, anterior cingulate cortex (ACC) and visual regions (V1, V2 and V3) were engaged during both ESL and ISL. With ESL there was increased activity in the visual regions on the predictable (i.e. learned pattern) trials. With ISL, however, there was a relative decrease in activity in visual regions. The opposite patterns in the visual regions highlight the different effects of ESL and ISL. The learning process was distinguished from the result of learning, by fitting subjects' functional magnetic resonance imaging data to their learning curve. This analysis revealed more extensive PFC activity during ESL and caudal ACC activity specific for the result of learning analysis, when the expected response was violated. Our results suggest a relative dissociation of the brain regions engaged during ESL and ISL, whereby ESL and ISL can be viewed as partially distinct but overlapping parallel processes.
Adolescent↗