Brain activation in highly superior autobiographical memory: The role of the precuneus in the autobiographical memory retrieval network.

This is the first study to examine functional brain activation in a single case of Highly Superior Autobiographical Memory (HSAM) who shows no sign of obsessive compulsive disorder (OCD). While previous work has documented the existence of HSAM, information about brain areas involved in this exceptional form of memory for personal events relies on structural and resting state connectivity data, with mixed results so far. In this first task-based functional magnetic resonance Imaging (fMRI) study of a normal individual with HSAM, dates were presented as cues and two phases were assessed during memory retrieval, initial access and later elaboration. Results showed that initial access was very fast, did not activate the hippocampus, and involved activation of predominantly posterior visual areas, including the precuneus. These areas typically become active during later stages of elaboration of personal memories rather than during initial access. Elaboration involved a balanced bilateral activation of most of the autobiographical network areas, rather than the more typical shifts observed in people without HSAM. Overall, the pattern of brain activations, which rests on repeated observations in a single individual, highlights a strong involvement of the precuneus and an idiosyncratic initial access to personal memory representations. Implications for the nature of personal memories in HSAM are discussed.

Confirmatory Factor Analysis of Neurocognitive Measures in Healthy Young Adults: The Relation of Executive Functions with Other Neurocognitive Functions.

OBJECTIVE: The present study aimed to investigate the factor structure of a set of neurocognitive tests theoretically assessing executive functions (EF), verbal abilities (VA), and processing speed (PS). This study extended previous research by analyzing if each test is better explained by the specific factor to which it theoretically belongs or by a more general neurocognitive factor; and also by analyzing the relations between the neurocognitive factors. METHODS: Using confirmatory factor analysis (CFA) we examined the factor structure of nine neurocognitive tests (EF: Working Memory, Tower, Divided Attention, Stroop, and Verbal Fluency tests; VA: Word List and Confrontation Naming tests; PS: Coding and Telephone Search tests) in a nonclinical sample (N = 90; 18-33 years old, 76 women). We tested five factor models of neurocognitive functioning: a one-factor model; two models with two-correlated factors; and two models with three-correlated factors. RESULTS: A three-correlated-factor model, with EF, VA, and PS factors, was the most suitable for our neuropsychological data. The Verbal Fluency test was better explained by the VA factor rather than by the EF factor. The EF factor was correlated with the PS factor, but not with the VA factor. CONCLUSIONS: Most of the neurocognitive measures used in the present study loaded in the expected factors (with the exception of the Verbal Fluency that was apparently more related to VA). EF and PS represent related but separable functions. Our results highlight the need for a careful interpretation of test scores since performance on one test usually requires multiple functions.

Cognitive control during a spatial Stroop task: Comparing conflict monitoring and prediction of response-outcome theories.

Cognitive control allows information processing and behaviour to vary adaptively from moment to moment depending on current goals. Two of the most prominent theories that have been proposed to account for the processing of cognitive control are the Conflict Monitoring Theory (CMT) and the Prediction of Response-Outcome Theory (PRO). According to both theories, the implementation of cognitive control during a trial in a conflict task reflects processing events that occurred in the preceding trial. Both CMT and PRO advocate that the detection of conflict situations leads to the recruitment of cognitive control, but they differ regarding the processing underpinnings of cognitive control during conflict resolution. CMT proposes that conflict between alternative responses is resolved by enhancing the task's relevant dimension, reducing interference from the task's irrelevant dimension(s). This control setup promotes conflict adaptation in the subsequent trial. PRO proposes that conflict is resolved by means of a cost-effectiveness analysis that identifies and suppresses action plans linked to the less appropriate responses, facilitating conflict resolution in the subsequent trial. To adjudicate between these alternatives, we manipulated contingencies pertaining to two-trial sequences (n-1; n), namely, the congruency between task relevant/irrelevant dimensions in trial n-1 and response repetition in trial n. A spatial Stroop task was used, in which task-relevant and irrelevant information were integrated within the same stimulus. In this task, participants were required to attend to the direction of an arrow while ignoring its position. The arrow's direction and position could be congruent (C) or incongruent (IC). In one experiment, trials in which the participant was required to respond according to the position of a circle (PO; position only trials), occupying the sequential position n, were the focus of the analyses. Three experiments were conducted manipulating the trials' sequence structure. In Experiment 1, we studied a low control/low conflict condition (cC trials), and two high control/low conflict conditions (icC with and without response repetition). In Experiment 2, we studied two low control/no conflict conditions (cPO with and without response repetition) and two high control/no conflict conditions (icPO with and without response repetition). In Experiment 3, we studied a high control/high conflict condition (icIC) and two low control/high conflict conditions (cIC with and without response repetition). Overall, our findings are in agreement with previous studies in which both bottom-up processing, linked to response and stimulus position repetition, and top-down processing, linked to cognitive control, were shown to contribute to sequence effects in conflict tasks. Specifically, our observations mainly support PRO's account of conflict resolution, in which the intervention of top-down processing is substantially more complex than in CMT's account.

Aging and the number sense: preserved basic non-symbolic numerical processing and enhanced basic symbolic processing.

Aging often leads to general cognitive decline in domains such as memory and attention. The effect of aging on numerical cognition, particularly on foundational numerical skills known as the number sense, is not well-known. Early research focused on the effect of aging on arithmetic. Recent studies have begun to investigate the impact of healthy aging on basic numerical skills, but focused on non-symbolic quantity discrimination alone. Moreover, contradictory findings have emerged. The current study aimed to further investigate the impact of aging on basic non-symbolic and symbolic numerical skills. A group of 25 younger (18-25) and 25 older adults (60-77) participated in non-symbolic and symbolic numerical comparison tasks. Mathematical and spelling abilities were also measured. Results showed that aging had no effect on foundational non-symbolic numerical skills, as both groups performed similarly [RTs, accuracy and Weber fractions (w)]. All participants showed decreased non-symbolic acuity (accuracy and w) in trials requiring inhibition. However, aging appears to be associated with a greater decline in discrimination speed in such trials. Furthermore, aging seems to have a positive impact on mathematical ability and basic symbolic numerical processing, as older participants attained significantly higher mathematical achievement scores, and performed significantly better on the symbolic comparison task than younger participants. The findings suggest that aging and its lifetime exposure to numbers may lead to better mathematical achievement and stronger basic symbolic numerical skills. Our results further support the observation that basic non-symbolic numerical skills are resilient to aging, but that aging may exacerbate poorer performance on trials requiring inhibitory processes. These findings lend further support to the notion that preserved basic numerical skills in aging may reflect the preservation of an innate, primitive, and embedded number sense.

Event-related brain potentials in the study of inhibition: cognitive control, source localization and age-related modulations.

In the previous 15 years, a variety of experimental paradigms and methods have been employed to study inhibition. In the current review, we analyze studies that have used the high temporal resolution of the event-related potential (ERP) technique to identify the temporal course of inhibition to understand the various processes that contribute to inhibition. ERP studies with a focus on normal aging are specifically analyzed because they contribute to a deeper understanding of inhibition. Three time windows are proposed to organize the ERP data collected using inhibition paradigms: the 200 ms period following stimulus onset; the period between 200 and 400 ms after stimulus onset; and the period between 400 and 800 ms after stimulus onset. In the first 200 ms, ERP inhibition research has primarily focused on N1 and P1 as the ERP components associated with inhibition. The inhibitory processing in the second time window has been associated with the N2 and P3 ERP components. Finally, in the third time window, inhibition has primarily been associated with the N400 and N450 ERP components. Source localization studies are analyzed to examine the association between the inhibition processes that are indexed by the ERP components and their functional brain areas. Inhibition can be organized in a complex functional structure that is not constrained to a specific time point but, rather, extends its activity through different time windows. This review characterizes inhibition as a set of processes rather than a unitary process.

Awareness and confabulation.

OBJECTIVE: A single case study with control and normative data of a 74-year-old retired businessman with amnestic mild cognitive impairment, who had spontaneous confabulations concerning fantastic exploits and magical powers as well as déjà vécu experiences. METHODS AND RESULTS: His neuropsychological profile showed episodic memory impairment including deficits of recent episodic autobiographical memories and of recognition, but performance was within normal limits on tests assessing source memory for words, the ability to suppress irrelevant items on a continuous recognition memory task, and the detection of stimulus frequency. There were discrete impairments in an ad hoc test measuring his ability to detect and discriminate the source of a range of material including information derived from personal and public events, invented material, and episodes culled from his personal reading. Although his source memory for autobiographical information was normal, he attributed 20% of the invented material and personal readings and 15% of the public events either to his own experience or to that of someone he knew personally or to someone else. CONCLUSIONS: This evidence suggests that none of the current theoretical accounts of spontaneous confabulations is sufficiently explanatory. Instead, an argument is developed that both fantastic confabulation and déjà vécu arose from a more fundamental disorder of awareness.

Event related potentials reveal that increasing perceptual load leads to increased responses for target stimuli and decreased responses for irrelevant stimuli.

Lavie (1995) have suggested that perceptual processing is influenced by perceptual load. Specifically, relevant information receives additional processing in high load situations exhausting the available capacity. On the other hand, irrelevant information receives less processing with increasing load on a relevant task, as there is a reduced amount of residual processing available. Rees et al. (1997) provided the first physiological evidence for this model, showing this pattern in a functional magnetic resonance imaging study. Likewise, Handy et al. (2001) offered supporting evidence measuring event related potentials (ERPs). Both of these studies presented irrelevant information in peripheral vision. Here we manipulated load while using the identical stimuli and the same task (a peripheral gap judgment task) with centrally presented irrelevant stimuli. ERPs show the pattern predicted by Lavie and colleagues, specifically for the N1 component. This work offers further evidence that visual attention modulates relatively early processing of perceptual information. Specifically, increasing load resulted in stronger N1 responses to relevant information and weaker N1 responses to irrelevant information.

Differential effects of aging on executive and automatic inhibition.

One of the major accounts of cognitive aging states that age effects are related to a deficiency of inhibitory mechanisms (Hasher & Zacks, 1988). Given that inhibition has traditionally been associated with the frontal cortex, and that the frontal cortex deteriorates early with age (Raz, 2000), this is consistent with the frontal hypothesis of aging (West, 1996). However, not all inhibitory processes require executive control, and so they are not all equally supported by the frontal cortex. As a consequence, one would expect dissociations between inhibitory tasks in the sense of a greater susceptibility of executive/frontal inhibition to aging. Based on Nigg's (2000) working inhibition taxonomy, we tested this hypothesis by combining inhibitory paradigms with different levels of executive control within the same participants. The results showed that age affects Stroop interference but not negative priming (Experiment 1) and stop signal responsiveness but not negative priming (Experiment 2). These findings suggest that tasks with a high executive (or effortful) inhibitory control are more sensitive to aging than tasks with a lower executive (more automatic) inhibitory control. The results are discussed in relation to the inhibitory and frontal accounts of aging.

The anatomical bases of semantic retrieval deficits in early Alzheimer's disease.

Semantic abilities deteriorate early in patients with Alzheimer's disease (AD) and their residual language is characterised by strong lexical effects such as the age of acquisition of words and their typicality. The anatomical bases of this early semantic degradation have not been fully explored. To clarify which neural structures, when atrophic, alter lexical-semantic function in patients with very mild AD, this study correlated the lexical attributes of words produced in a semantic fluency task with grey matter density values from 3D MRI scans of mild AD patients. The voxel-based analyses showed a significant correlation between the lexical attributes characterising residual linguistic production in early AD patients and the integrity of regions of the medial temporal lobes, especially in areas of the perirhinal and parahippocampal cortex. This correlation was present in both hemispheres. There were no correlations within these structures with scores on neuropsychological tests not involving semantic or episodic memory. The results have implications for the role of medial temporal structures in episodic and semantic retrieval and argue against a unitary function of these structures in respect of episodic and semantic memory processes. This evidence suggests that specialised regions within the hippocampal complex engage in processes of encoding and retrieval for both semantic and episodic memories.

Temporal and spatio-temporal attention to tactile stimuli in extinction patients.

The temporal deployment of attention to tactile stimuli delivered to the same or to a symmetrical position of the body was assessed in 6 Right-Brain Damaged (RBD) patients with left tactile extinction and 6 healthy controls. Two different tasks called Temporal (T) and Spatio-Temporal (ST) extinction were used. In the T task single or double electro tactile stimuli were delivered to the same point to the left or, in separate blocks, to the right index finger. Double stimuli were separated by different Stimulus Onset Asynchronies (SOAs). In the ST task, stimuli could be single (left or right) or double (left and right). Double stimuli were delivered to the index finger of both hands simultaneously or sequentially. In both tasks subjects were asked to report the number of the stimuli they perceived. In the ST task, subjects were also requested to report the stimuli location. Results show that in both tasks RBD patients' detection of left sided stimuli was significantly lower than of right sided stimuli detection, mainly at shortest SOAs. Moreover, detection of left sided stimuli was higher when two stimuli were delivered in sequence and in symmetrical body areas and in different sides of the space than when stimuli were delivered in sequence in the same body area. Results suggest that the interaction between spatial and temporal variables enhances the ability of tactile extinction patients to detect left sided stimuli.

Dissociation between taste and tactile extinction on the tongue after right brain damage.

In patients with right brain damage (RBD) or left brain damage (LBD) and healthy subjects, tactile and three basic gustatory stimuli (sour, salty, bitter) were applied to the left or right hemitongues or to both hemitongues simultaneously. Tactile stimuli were detected and localized by verbal report, whereas gustatory stimuli were identified by pointing to the corresponding name on cards bearing the names of the three tastes. In the tactile test, 9 of 18 RBD patients showed extinction of left hemitongue stimuli, whereas the remaining RBD patients, 9 LBD patients and 14 healthy subjects detected virtually all stimuli in all conditions. In the gustatory test, healthy subjects outperformed the two brain damaged groups which nevertheless responded well above chance and did not differ from one another. Unexpectedly, the nine RBD patients with left hemitongue tactile extinction showed no gustatory extinction, since performance did not differ significantly between the two hemitongues on both unilateral and bilateral stimulations. To account for these findings, some evidence suggests that the tongue representation is bilateral in both modalities, but predominantly ipsilateral in the gustatory modality and predominantly contralateral in the tactile modality. The RBD patients with left hemitongue tactile extinction were those with more marked symptoms of left-sided extinction in the visual and auditory modalities, making it likely that their brain damage was also responsible for left lingual tactile extinction. The absence of left gustatory extinction in those patients can be attributed to the predominant channelling of left hemitongue taste inputs into the intact left hemisphere.

Temporal modulation of spatial tactile extinction in right-brain-damaged patients.

Unilateral and bilateral electrotactile stimuli were delivered to both hands of 11 right-brain-damaged (RBD) patients with left tactile extinction and 20 healthy subjects. Bimanual stimuli could be presented simultaneously or with varying stimulus onset asynchronies (SOAs). Subjects indicated their detection of unilateral or bilateral stimuli, their judgements of whether stimuli were simultaneous or successive, and, in the latter case, which side came first. In RBD patients, extinction was maximal with simultaneous presentations and decreased as SOA increased. With short SOAs, omissions of left-sided stimuli occurred with both right-side and left-side stimulus precedence, suggesting a forward and backward interference of the right stimulus on the processing of the left stimulus within a time window of at least 100 msec. In contrast, there was no interference of the left stimulus on the detection of the right stimulus. Unlike controls, extinction patients rarely expressed simultaneity judgements, but those that were produced tended to be veridical or nearly so, like in normal controls. Whereas controls expressed generally accurate judgements of right or left precedence, patients showed a bias toward a right precedence and a maximal uncertainty between left-first and right-first choices when the left stimulus had a lead between 100 and 200 msec. The results are consistent with the hypothesis that, as in other sensory modalities, tactile extinction is associated with an abnormal persistent bias of attention toward the ipsilesional side that delays the processing of contralesional stimuli. However, the finding that both extinction and explicit judgements of simultaneity tended to occur with simultaneous bilateral stimuli suggest the presence of some residual neural capacity to detect precise temporal coincidence.