Brain activation while thinking about the self from another person’s perspective after traumatic brain injury in adolescents.

Deficits in self awareness and taking the perspective of others are often observed following traumatic brain injury (TBI). Nine adolescents (ages 12–19 years) who had sustained moderate to severe TBI after an average interval of 2.6 years and nine typically developing (TD) adolescents underwent functional MRI (fMRI) while performing a perspective taking task (D’Argembeau et al., 2007). Participants made trait attributions either from their own perspective or from that of the significant other. The groups did not differ in reaction time or on a consistency criterion. When thinking of the self from a third-person perspective, adolescents with TBI demonstrated greater activation in posterior brain regions implicated in social cognition, the left lingual gyrus (BA 18) and posterior cingulate (BA 31), extending into neighboring regions not generally associated with social cognition, that is, cuneus (BA 31) and parahippocampal gyrus, relative to TD adolescents. We postulate that adolescents with moderate to severe TBI recruited alternative neural pathways during perspective-taking because traumatic axonal injury disrupted their fronto-parietal networks mediating social cognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive resources and dual-task interference effects at retrieval in normal people: The role of the frontal lobes and medial temporal cortex.

Conducted 3 experiments to examine the hypothesis that concurrent secondary tasks at retrieval will interfere more with long-term, episodic memory functions involving the frontal lobes than those involving the medial temporal lobes hippocampus (MTL/H). The rationale is that strategic retrieval processes mediated by the frontal lobes place greater demands on cognitive resources than do relatively automatic associative retrieval processes (ecphory) mediated by the temporal lobes. In Exps 1 and 2, sequential finger tapping was performed at encoding, at retrieval, at both, or at neither. Recall of a categorized list of 16 words from the California Verbal Learning Test in Exp 1, and release from proactive inhibition (PI) in Exp 2, both being tests that involve the frontal lobes, were impaired if normal Ss tapped at both encoding and retrieval. Concurrent tapping had little effect on rate of learning in Exp 1 and on total words recalled during the buildup of PI in Exp 2, both of which are indices that are affected more by MTL/H than by frontal lesions. In Exp 3, tapping by normal Ss affected letter fluency, a test more sensitive to frontal lobe than temporal lobe damage, but not category fluency, for which the reverse is true. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Access and organization of goal-derived categories after traumatic brain injury

This study examined the access and organization of goal-derived categories in semantic memory with a group of chronic traumatic brain injured TBI adults and a group of age and gender-matched neurologically-intact controls. Goal-derived categories are developed by individuals for use in specialized contexts to achieve a goal, such as 'things to take on a camping trip.' Categories were presented to subjects in two task contexts: category verification and exemplar generation. Overall, the TBI subjects were able to accurately identify and organize category exemplars within particular categories. Interestingly, the TBI subjects produced significantly more total responses than the neurologically-intact subjects on exemplar generation; however, a high percentage of their responses (one-third) were inaccurate, consisting of out-of-set responses and repetitions. These findings suggest that difficulties in retrieval may exist in the presence of relatively intact access and organization of goal-derived category structure. The results are discussed relative to deficits in the executive control of verifying goal-directed behaviour and incomplete category representation.     

Self and parent ratings of executive functioning after adolescent traumatic brain injury.

Objective: To examine the level of agreement between adolescents with traumatic brain injury (TBI) and their parents in standardized ratings of executive functioning, and to determine correlates of discrepancies between those ratings. Participants: Ninety-eight 11- to 16-year-old adolescents with TBI and their parents, and 97 neuropsychologically healthy controls. Method: Five-year consecutive series of rehabilitation referrals for TBI. Measures: Behavior Rating Inventory of Executive Function–Self Report (BRIEF–SR) and Behavior Rating Inventory of Executive Function (BRIEF) parent report versions. Results: Self and parent ratings were moderately positively correlated in both the TBI group and the control group, but parents generally identified more executive dysfunction than did the adolescents. Parent-adolescent discrepancies were statistically significantly greater in the TBI group than in the control group on the Metacognitive index but not the Behavioral Regulation index. The degree of the former discrepancy was predicted by duration of coma in the TBI group. Conclusions: Adolescents with more severe TBI may underestimate their own degree of executive dysfunction in daily life, particularly aspects of metacognitive abilities, possibly, in part, because of an organic-based lack of deficit awareness. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Diluting the burden of load: Perceptual load effects are simply dilution effects.

The substantial distractor interference obtained for small displays when the target appears alone is reduced in large displays when the target is embedded among neutral letters. This finding has been interpreted as reflecting low-load and high-load processing, respectively, thereby supporting the theory of perceptual load (Lavie & Tsal, 1994). However, a possible alternative interpretation of this effect is that the distractor is similarly processed in both displays, yet its interference in the large ones is diluted by the presence of the neutral letters. We separated the effects of load and dilution by introducing dilution displays. They contained as many letters as the high-load displays but were clearly distinguished from the target, thus allowing for a low-load processing mode. Distractor interference obtained under both the low-load and high-load conditions disappeared under the dilution condition. Hence, the display size effect traditionally misattributed to perceptual load is fully accounted for by dilution. Furthermore, when dilution is controlled for, it is high load not low load producing greater interference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Encoding and retrieval processes in velo-cardio-facial syndrome (VCFS).

Velo-cardio-facial syndrome (VCFS) is a neurogenetic disorder associated with very high risk for developing schizophrenia. More than half of affected individuals experience transient psychotic symptoms during childhood and a third may develop schizophrenia. Memory regulation deficits disturbing both the encoding and retrieval stages of memory represent core deficits in the cognitive profile associated with schizophrenia. In this study, the authors investigate memory regulation processes in 33 individuals with VCFS along with 33 age- and sex-matched control participants. By using a directed forgetting paradigm and a continuous recognition paradigm, the authors examined selective encoding and suppression of irrelevant contents during retrieval in VCFS. Group comparison analyses revealed comparable performances on selective encoding and recognition accuracy between the VCFS group and control group. However, individuals with VCFS were more likely to make false recognitions and showed deficits in the suppression of irrelevant contents. Results suggest that trait-like deficits of memory regulation in VCFS can be observed during the retrieval stage, while selective encoding remains efficient. Memory regulation processes during retrieval may constitute a trait deficit in the memory profile of individuals with VCFS and may contribute to the cognitive deficits underlying an increased risk for developing schizophrenia in this population. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Source memory in older adults: An encoding or retrieval problem?

Source memory has been found to be more affected by aging than item memory, possibly because of declining frontal function among older adults. In 4 experiments, the authors explored the role of the frontal lobes (FLs) in source memory, the extent to which they may be involved in the encoding and/or retrieval of source or context, and the conditions under which the source memory deficit in older people may be reduced or eliminated. Results indicated that only a subset of older adults show deficits in source memory, namely those with below average frontal function, and these deficits can be eliminated by requiring people at study to consider the relation between an item and its context. These results provide convincing evidence of the importance of frontal function during the encoding of source and suggest that older adults with reduced FL function fail to initiate the processes required to integrate contextual information with focal content during study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrieval during learning facilitates subsequent memory encoding.

In multiple-list learning, retrieval during learning has been suggested to improve recall of the single lists by enhancing list discrimination and, at test, reducing interference. Using electrophysiological, oscillatory measures of brain activity, we examined to what extent retrieval during learning facilitates list encoding. Subjects studied 5 lists of items in anticipation of a final cumulative recall test and did either a retrieval or a no-retrieval task between study of the lists. Retrieval was from episodic memory (recall of the previous list), semantic memory (generation of exemplars from an unrelated category), or short-term memory (2-back task). Behaviorally, all 3 forms of retrieval enhanced recall of both previously and subsequently studied lists. Physiologically, the results showed an increase of alpha power (8–14 Hz) from List 1 to List 5 encoding when no retrieval activities were interpolated but no such increase when any of the 3 retrieval activities occurred. Brain–behavior correlations showed that alpha-power dynamics from List 1 to List 5 encoding predicted subsequent recall performance. The results suggest that, without intermittent retrieval, encoding becomes ineffective across lists. In contrast, with intermittent retrieval, there is a reset of the encoding process for each single list that makes encoding of later lists as effective as encoding of early lists. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of traumatic brain injury on the cholinergic system in the rat

Rats subjected to a mild to moderate fluid percussion injury exhibit memory deficits that are similar to rats that have received lesions of the septohippocampal system. Because the cholinergic system plays a major role in septohippocampal function, we studied the kinetics of the synthetic enzyme for acetylcholine, choline acetyltransferase (ChAT), at 1 h, 24 h, or 5 days after a fluid percussion injury. Decreases in ChAT activity were found in the dorsal hippocampus (25%), frontal (32%), and temporal (23%) cortices 1 h after injury. In the parietal cortex, a greater than 50% increase in ChAT activity was observed at all time intervals assessed. At 5 days after TBI, there was an 18% increase in ChAT activity in the medial septal area. These data provide evidence that a mild to moderate fluid percussion injury produces changes in the cholinergic system in brain areas related to memory.     

Aging effects on memory encoding in the frontal lobes.

Functional magnetic resonance imaging (fMRI) was used to compare frontal-lobe activation in younger and older adults during encoding of words into memory. Participants made semantic or nonsemantic judgements about words. Younger adults exhibited greater activation for semantic relative to nonsemantic judgements in several regions, with the largest activation in the left inferior frontal gyrus. Older adults exhibited greater activation for semantic judgments in the same regions, but the extent of activation was reduced in left prefrontal regions. In older adults, there was a significant association between behavioral tests of declarative and working memory and extent of frontal activation. These results suggest that age-associated decreases in memory ability may be due to decreased frontal-lobe contributions to the initial encoding of experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain regions supporting intentional and incidental memory: a PET study

Regional brain activity associated with intentional and incidental memory retrieval was studied with PET. Previously studied and new words were presented in either an intentional or an incidental memory task. Type of task was crossed with an encoding manipulation ('deep' vs 'shallow') which varied the probability that studied items would be remembered. In both tasks, deeply encoded items were associated with greater activation in the left hippocampus than were items that had received shallow encoding, suggesting that the involvement of the hippocampus in memory retrieval is independent of whether remembering is intentional or incidental. Right prefrontal and bilateral parietal cortex were more activated during the international task than during the incidental task, irrespective of encoding condition. Thus, these regions play a more extensive role in memory retrieval when remembering is intentional.     

Task-related and item-related brain processes of memory retrieval

In all cognitive tasks, general task-related processes operate throughout a given task on all items, whereas specific item-related processes operate differentially on individual items. In typical functional neuroimaging experiments, these two sets of processes have usually been confounded. Herein we report a combined positron emission tomography and event-related potential (ERP) experiment that was designed to distinguish between neural correlates of task-related and item-related processes of memory retrieval. Two retrieval tasks, episodic and semantic, were crossed with episodic (old/new) and semantic (living/nonliving) properties of individual items to yield evidence of regional brain activity associated with task-related processes, item-related processes, and their interaction. The results showed that episodic retrieval task was associated with increased blood flow in right prefrontal and posterior cingulate cortex, as well as with a sustained right-frontopolar-positive ERP, but that the semantic retrieval task was associated with left frontal and temporal lobe activity. Retrieval of old items was associated with increased blood flow in the left medial temporal lobe and with a brief late positive ERP component. The results provide converging hemodynamic and electrophysiological evidence for the distinction of task- and item-related processes, show that they map onto spatially and temporally distinct patterns of brain activity, and clarify the hemispheric encoding/retrieval asymmetry (HERA) model of prefrontal encoding and retrieval asymmetry.     

Adult age differences in the functional neuroanatomy of verbal recognition memory

Adult age differences are frequently observed in the performance of memory tasks, but the changes in neural function mediating these differences are largely unknown. We used (H2)15O positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) during Encoding, Baseline, and Retrieval conditions of a recognition memory task. Twelve young adults (20-29 years) and 12 older adults (62-79 years) participated. During each task condition, participants made a two-choice manual response to each of 64 words. Analyses of the performance data yielded evidence of age-related slowing of encoding and retrieval processes, and an age-related decline in the accuracy of yes/no recognition (d'). The rCBF activation associated with both encoding and retrieval was greater for older adults than for young adults, but this pattern was more clearly evident for memory retrieval. For young adults, rCBF activation during retrieval occurred primarily in right prefrontal cortex, whereas older adults exhibited a more bilateral pattern of prefrontal activation. Regression analyses predicting reaction time in the memory task from regional PET counts confirmed that the neural system mediating memory retrieval is more widely distributed for older adults than for young adults. Both age groups exhibited some decrease in rCBF activation in the second half of the test session, relative to the first half. The practice-related decrease in rCBF activation was more prominent for young adults, suggesting that the older adults' recruitment of additional neural systems reflects a more continual allocation of attention to support task performance.     

Temporal dynamics of brain activation during a working memory task

Working memory is responsible for the short-term storage and online manipulation of information necessary for higher cognitive functions, such as language, planning and problem-solving. Traditionally, working memory has been divided into two types of processes: executive control (governing the encoding manipulation and retrieval of information in working memory) and active maintenance (keeping information available 'online'). It has also been proposed that these two types of processes may be subserved by distinct cortical structures, with the prefrontal cortex housing the executive control processes, and more posterior regions housing the content-specific buffers (for example verbal versus visuospatial) responsible for active maintenance. However, studies in non-human primates suggest that dorsolateral regions of the prefrontal cortex may also be involved in active maintenance. We have used functional magnetic resonance imaging to examine brain activation in human subjects during performance of a working memory task. We used the temporal resolution of this technique to examine the dynamics of regional activation, and to show that prefrontal cortex along with parietal cortex appears to play a role in active maintenance.     

Working-memory capacity, proactive interference, and divided attention: Limits on long-term memory retrieval.

Two experiments examined how individual differences in working-memory capacity (WM) relate to proactive interference (PI) susceptibility. We tested high and low WM-span participants in a PI-buildup task under single-task or dual-task ("load") conditions. In Experiment 1, a finger-tapping task was imposed during encoding and retrieval of each list; in Experiment 2, tapping was required during encoding or retrieval. In both experiments, low spans showed greater PI than did high spans under no load, but groups showed equivalent PI under divided attention. Load increased PI only for high spans, suggesting they use attention at encoding and retrieval to combat PI. In Experiment 2, only low spans showed a dual-task cost on List 1 memory, before PI built up. Results indicate a role for attentional processing, perhaps inhibitory in nature, at encoding and retrieval, and are discussed with respect to theories of WM and prefrontal cortex function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The attentional demands of encoding and retrieval in younger and older adults: I. Evidence from divided attention costs.

Four studies examined the effects of divided attention in younger and older adults. Attention was divided at encoding or retrieval in free recall (Experiment 1), cued recall (Experiments 2 and 3), and recognition (Experiment 4). Dividing attention at encoding disrupted memory performance equally for the two age groups; by contrast, for both age groups, dividing attention at retrieval had little or no effect on memory performance. Secondary task reaction times (RTs) were slowed to a greater extent for the older adults than for the younger adults, especially at retrieval. Age-related differences in RTs costs at retrieval were largest in free recall, smaller in cued recall, and smallest in recognition. These results provide evidence for an age-related increase in the attentional demands of encoding and retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A rational approach to managing stage I nonseminomatous germ cell cancer

Four studies examined the effects of divided attention in younger and older adults. Attention was divided at encoding or retrieval in free recall (Experiment 1), cued recall (Experiments 2 and 3), and recognition (Experiment 4). Dividing attention at encoding disrupted memory performance equally for the two age groups; by contrast, for both age groups, dividing attention at retrieval had little or no effect on memory performance. Secondary task reaction times (RTs) were slowed to a greater extent for the older adults than for the younger adults, especially at retrieval. Age-related differences in RT costs at retrieval were largest in free recall, smaller in cued recall, and smallest in recognition. These results provide evidence for an age-related increase in the attentional demands of encoding and retrieval.     

Emotion-attention interactions in recognition memory for distractor faces.

Effective filtering of distractor information has been shown to be dependent on perceptual load. Given the salience of emotional information and the presence of emotion-attention interactions, we wanted to explore the recognition memory for emotional distractors especially as a function of focused attention and distributed attention by manipulating load and the spatial spread of attention. We performed two experiments to study emotion-attention interactions by measuring recognition memory performance for distractor neutral and emotional faces. Participants performed a color discrimination task (low-load) or letter identification task (high-load) with a letter string display in Experiment 1 and a high-load letter identification task with letters presented in a circular array in Experiment 2. The stimuli were presented against a distractor face background. The recognition memory results show that happy faces were recognized better than sad faces under conditions of less focused or distributed attention. When attention is more spatially focused, sad faces were recognized better than happy faces. The study provides evidence for emotion-attention interactions in which specific emotional information like sad or happy is associated with focused or distributed attention respectively. Distractor processing with emotional information also has implications for theories of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Clarifying the factors that undermine behavioral inhibition system functioning in psychopathy.

Psychopathic individuals are generally unresponsive to motivational and emotional cues that facilitate behavioral regulation. A putative mechanism for this deficiency is Gray's (1981) behavioral inhibition system (BIS). To evaluate the association between psychopathy and BIS functioning, we administered a laboratory-based assessment of BIS functioning to a group of psychopathic offenders assessed with the Psychopathy Checklist–Revised (PCL–R; Hare, 2003). In addition, we tested the hypothesis that the effects of working memory load on BIS functioning would interact differentially with the PCL–R factors. Replicating previous results, psychopathic offenders were less sensitive to BIS-related cues than controls. As predicted, working memory load interacted with Factor 2 (antisocial/impulsive), with higher scores predicting weaker BIS functioning under high-load though not low-load conditions. Results suggest new insights concerning the relationship among working memory, reward sensitivity, and BIS functioning in psychopathy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Material-specific lateralization of prefrontal activation during episodic encoding and retrieval

Although numerous neuroimaging studies have examined the functional neuroanatomy supporting episodic memory for verbal material, there have been few investigations of non-verbal episodic encoding and retrieval. We used fMRI to directly compare prefrontal activation elicited by verbal and non-verbal material during encoding and during retrieval. Regardless of the mnemonic operation (encoding/retrieval), inferior prefrontal activation lateralized based on material type. Verbal encoding and retrieval resulted in greater left inferior prefrontal activation, whereas non-verbal encoding and retrieval resulted in greater right inferior prefrontal activation. The similarity between inferior prefrontal activity during encoding and during retrieval indicates that these mnemonic operations depend on shared processes mediated by inferior prefrontal regions.