Chiara Guerrini

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 Niggs (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 Alzheimers 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.

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.

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.

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.

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.