Residual cognitive deficits 50 years after lead poisoning during childhood

The long term neurobehavioural consequences of childhood lead poisoning are not known. In this study adult subjects with a documented history of lead poisoning before age 4 and matched controls were examined with an abbreviated battery of neuropsychological tests including measures of attention, reasoning, memory, motor speed, and current mood. The subjects exposed to lead were inferior to controls on almost all of the cognitive tasks. This pattern of widespread deficits resembles that found in children evaluated at the time of acute exposure to lead rather than the more circumscribed pattern typically seen in adults exposed to lead. Despite having completed as many years of schooling as controls, the subjects exposed to lead were lower in lifetime occupational status. Within the exposed group, performance on the neuropsychological battery and occupational status were related, consistent with the presumed impact of limitations in neuropsychological functioning on everyday life. The results suggest that many subjects exposed to lead suffered acute encephalopathy in childhood which resolved into a chronic subclinical encephalopathy with associated cognitive dysfunction still evident in adulthood. These findings lend support to efforts to limit exposure to lead in childhood

A comparison of magnetic resonance imaging and neuropsychological examination in the diagnostic distinction of Alzheimer’s disease and behavioral variant frontotemporal dementia

The clinical distinction between Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) remains challenging and largely dependent on the experience of the clinician. This study investigates whether objective machine learning algorithms using supportive neuroimaging and neuropsychological clinical features can aid the distinction between both diseases. Retrospective neuroimaging and neuropsychological data of 166 participants (54 AD; 55 bvFTD; 57 healthy controls) was analyzed via a Naïve Bayes classification model. A subgroup of patients (n = 22) had pathologically-confirmed diagnoses. Results show that a combination of gray matter atrophy and neuropsychological features allowed a correct classification of 61.47% of cases at clinical presentation. More importantly, there was a clear dissociation between imaging and neuropsychological features, with the latter having the greater diagnostic accuracy (respectively 51.38 vs. 62.39%). These findings indicate that, at presentation, machine learning classification of bvFTD and AD is mostly based on cognitive and not imaging features. This clearly highlights the urgent need to develop better biomarkers for both diseases, but also emphasizes the value of machine learning in determining the predictive diagnostic features in neurodegeneration

What does a cue do? Comparing phonological and semantic cues for picture naming in aphasia

Purpose: Impaired naming is one of the most common symptoms in aphasia, often treated with cued picture naming paradigms. It has been argued that semantic cues facilitate the reliable categorisation of the picture, and phonological cues facilitate the retrieval of target phonology. To test these hypotheses, we compared the effectiveness of phonological and semantic cues in picture naming for a group of individuals with aphasia. To establish the locus of effective cueing, we also tested whether cue type interacted with lexical and image properties of the targets. Method: Individuals with aphasia (n=10) were tested with a within-subject design. They named a large set of items (n=175) four times. Each presentation of the items was accompanied by a different cueing condition (phonological, semantic, non-associated word and tone). Item level variables for the targets (i.e., phoneme length, frequency, imageability, name agreement and visual complexity) were used to test the interaction of cue type and item variables. Naming accuracy data was analysed using generalised linear mixed effects models. Results: Phonological cues were more effective than semantic cues, improving accuracy across individuals. However, phonological cues did not interact with phonological or lexical aspects of the picture names (e.g., phoneme length, frequency). Instead, they interacted with properties of the picture itself (i.e., visual complexity), such that phonological cues improved naming accuracy for items with low visual complexity. Conclusions: The findings challenge the theoretical assumptions that phonological cues map to phonological processes. Instead, phonological information benefits the earliest stages of picture recognition, aiding the initial categorization of the target. The data help to explain why patterns of cueing are not consistent in aphasia, i.e., it is not the case that phonological impairments always benefit from phonological cues and semantic impairments form semantic cues. A substantial amount of the literature in naming therapy focuses on picture naming paradigms. Therefore, the results are also critically important for rehabilitation, allowing for therapy development to be more rooted in the true mechanisms through which cues are processed

Visual processing speed is linked to functional connectivity between right frontoparietal and visual networks

Visual information processing requires an efficient visual attention system. The neural theory of visual attention (TVA) proposes that visual processing speed depends on the coordinated activity between frontoparietal and occipital brain areas. Previous research has shown that the coordinated activity between (i.e., functional connectivity and “inter-FC”) cingulo-opercular (COn) and right-frontoparietal (RFPn) networks is linked to visual processing speed. However, how inter-FC of COn and RFPn with visual networks links to visual processing speed has not been directly addressed yet. Forty-eight healthy adult participants (27 females) underwent resting-state (rs-)fMRI and performed a whole-report psychophysical task. To obtain inter-FC, we analyzed the entire frequency range available in our rs-fMRI data (i.e., 0.01–0.4 Hz) to avoid discarding neural information. Following previous approaches, we analyzed the data across frequency bins (Hz): Slow-5 (0.01–0.027), Slow-4 (0.027–0.073), Slow-3 (0.073–0.198), and Slow-2 (0.198–0.4). We used the mathematical TVA framework to estimate an individual, latent-level visual processing speed parameter. We found that visual processing speed was negatively associated with inter-FC between RFPn and visual networks in Slow-5 and Slow-2, with no corresponding significant association for inter-FC between COn and visual networks. These results provide the first empirical evidence that links inter-FC between RFPn and visual networks with the visual processing speed parameter. These findings suggest that direct connectivity between occipital and right frontoparietal, but not frontoinsular, regions support visual processing speed

The effect of age on recollection is not moderated by differential estimation methods

Episodic memory performance declines with increasing age. It has sometimes been reported that this decline is more marked when episodic recollection is estimated by “objective” measures such as source memory performance than when it is estimated by “subjective” measures such as the “Remember/Know” procedure. Here, our main goal was to directly contrast recollection estimates derived from these procedures in the same samples of young and older participants (24 adults per age group, within-subjects manipulation of test procedure). Following identical study phases in which words were paired with either faces or scenes, participants’ memories were assessed in separate test blocks using either Remember/Know or source memory procedures. Contrary to several prior reports, the deleterious effects of age on recollection estimates did not differ according to test type. Thus, we found no evidence that age differentially impacts subjective and objective recollection estimates. Additionally, and consistent with prior findings, effects of age on estimates of familiarity-driven recognition were small and non-significant

Neural Substrates of Semantic Prospection – Evidence from the Dementias

The ability to envisage personally relevant events at a future time point represents an incredibly sophisticated cognitive endeavor and one that appears to be intimately linked to episodic memory integrity. Far less is known regarding the neurocognitive mechanisms underpinning the capacity to envisage non-personal future occurrences, known as semantic future thinking. Moreover the degree of overlap between the neural substrates supporting episodic and semantic forms of prospection remains unclear. To this end, we sought to investigate the capacity for episodic and semantic future thinking in Alzheimer’s disease (n = 15) and disease-matched behavioral-variant frontotemporal dementia (n = 15), neurodegenerative disorders characterized by significant medial temporal lobe (MTL) and frontal pathology. Participants completed an assessment of past and future thinking across personal (episodic) and non-personal (semantic) domains, as part of a larger neuropsychological battery investigating episodic and semantic processing, and their performance was contrasted with 20 age- and education-matched healthy older Controls. Participants underwent whole-brain T1-weighted structural imaging and voxel-based morphometry analysis was conducted to determine the relationship between gray matter integrity and episodic and semantic future thinking. Relative to Controls, both patient groups displayed marked future thinking impairments, extending across episodic and semantic domains. Analyses of covariance revealed that while episodic future thinking deficits could be explained solely in terms of episodic memory proficiency, semantic prospection deficits reflected the interplay between episodic and semantic processing. Distinct neural correlates emerged for each form of future simulation with differential involvement of prefrontal, lateral temporal, and medial temporal regions. Notably, the hippocampus was implicated irrespective of future thinking domain, with the suggestion of lateralization effects depending on the type of information being simulated. Whereas episodic future thinking related to right hippocampal integrity, semantic future thinking was found to relate to left hippocampal integrity. Our findings support previous observations of significant MTL involvement for semantic forms of prospection and point to distinct neurocognitive mechanisms which must be functional to support future-oriented forms of thought across personal and non-personal contexts

Functional outcome is tied to dynamic brain states after mild to moderate traumatic brain injury

The current study set out to investigate the dynamic functional connectome in relation to long-term recovery after mild to moderate traumatic brain injury (TBI). Longitudinal resting-state functional MRI data were collected (at 1 and 3 months postinjury) from a prospectively enrolled cohort consisting of 68 patients with TBI (92% mild TBI) and 20 healthy subjects. Patients underwent a neuropsychological assessment at 3 months postinjury. Outcome was measured using the Glasgow Outcome Scale Extended (GOS-E) at 6 months postinjury. The 57 patients who completed the GOS-E were classified as recovered completely (GOS-E = 8; n = 37) or incompletely (GOS-E < 8; n = 20). Neuropsychological test scores were similar for all groups. Patients with incomplete recovery spent less time in a segregated brain state compared to recovered patients during the second visit. Also, these patients moved less frequently from one meta-state to another as compared to healthy controls and recovered patients. Furthermore, incomplete recovery was associated with disruptions in cyclic state transition patterns, called attractors, during both visits. This study demonstrates that poor long-term functional recovery is associated with alterations in dynamics between brain networks, which becomes more marked as a function of time. These results could be related to psychological processes rather than injury-effects, which is an interesting area for further work. Another natural progression of the current study is to examine whether these dynamic measures can be used to monitor treatment effects