Orienting of spatial attention in Huntington's Disease

Graph methods to infer spatial disturbances: Application to Huntington's Disease's speech

OBJECTIVE

Huntington's Disease (HD) is an inherited neurodegenerative disease caused by the mutation of the Htt gene, impacting all aspects of living and functioning. Among cognitive disabilities, spatial capacities are impaired, but their monitoring remains scarce as limited by lengthy experts' assessments. Language offers an alternative medium to evaluate patients' performance in HD. Yet, its capacities to assess HD's spatial abilities are unknown. Here, we aimed to bring proof-of-concept that HD's spatial deficits can be assessed through speech.

METHODS

We developed the Spatial Description Model to graphically represent spatial relations described during the Cookie Theft Picture (CTP) task. We increased the sensitivity of our model by using only sentences with spatial terms, unlike previous studies in Alzheimer's disease. 78 carriers of the mutant Htt, including 56 manifest and 22 premanifest individuals, as well as 25 healthy controls were included from the BIOHD & (NCT01412125) & Repair-HD (NCT03119246) cohorts. The convergence and divergence of the model were validated using the SelfCog battery.

RESULTS

Our Spatial Description Model was the only one among the four assessed approaches, revealing that individuals with manifest HD expressed fewer spatial relations and engaged in less spatial exploration compared to healthy controls. Their graphs correlated with both visuospatial and language SelfCog performances, but not with motor, executive nor memory functions.

CONCLUSIONS

We provide the proof-of-concept using our Spatial Description Model that language can grasp HD patient's spatial disturbances. By adding spatial capabilities to the panel of functions tested by the language, it paves the way for eventual remote clinical application.

Striatum and language processing: Where do we stand?

More than a century ago, Broca (1861), Wernicke (1874) and Lichteim (1885) laid the foundations for the first anatomo-functional model of language, secondarily enriched by Geschwind (1967), leading to the Broca-Wernicke-Lichteim-Geschwind model. This model included the frontal, parietal, and temporal cortices as well as a subcortical structure, which could be the striatum, whose nature and role have remained unclear. Although the emergence of language deficits in patients with striatal injury has challenged the cortical language models developed over the past 30 years, the integration of the striatum into language processing models remains rare. The main argument for not including the striatum in language processing is that the disorders observed in patients with striatal dysfunction may result from the striatal role in cognitive functions beyond language, and not from the impairment of language itself. Indeed, unraveling the role of the striatum and the frontal cortex, linked by the fronto-striatal pathway, is a challenge. Here, we first reviewed the studies that explored the link between striatal functions and the different levels of language (phonetics, phonology, morphology, syntax, and lexico-semantics). We then looked at the language models, which included the striatum, and found that none of them captured the diversity of experimental data in this area. Finally, we propose an integrative anatomo-functional model of language processing combining traditional language processing levels and some "executive" functions, known to improve the efficiency and fluidity of language: control, working memory, and attention. We argue that within this integrative model, the striatum is a central node of a verbal executive network that regulates, monitors, and controls the allocations of limited cognitive resources (verbal working memory and verbal attention), whatever the language level. This model combines data from neurology, psycholinguistics, and cognitive science.

Visual Dysfunction in Huntington's Disease: A Systematic Review

It is well-documented that patients with Huntington's disease (HD) exhibit specific deficits in visual cognition. A less well-documented literature also exists that suggests people with HD experience a number of disease-related changes to more rudimentary sensory visual processing. Here, we review evidence for the effects of HD on the integrity of the early visual pathways in humans along with changes to low-level visual sensitivity. We find evidence for reduced structural and functional integrity of the visual pathways, marked by retinal thinning, reduced VEP amplitude, and cell loss and thinning in visual cortex. We also find evidence of visual perceptual deficits, particularly for colour and motion. We suggest that future studies with well-defined HD and HD-related groups in appropriate numbers that systematically examine the relationship between structural changes to the visual system, basic visual perceptual deficits and disease stage/severity are therefore likely to yield promising results.

Impaired functional default mode network in patients with mild neurological Wilson's disease

Wilson's disease (WD) is an autosomal recessive metabolic disorder characterized by cognitive, psychiatric and motor signs and symptoms that are associated with structural and pathological brain abnormalities, in addition to liver changes. However, functional brain connectivity pattern of WD patients remains largely unknown. In the present study, we investigated functional brain connectivity pattern of WD patients using resting state functional magnetic resonance imaging. Particularly, we studied default mode network (DMN) using posterior cingulate cortex (PCC) based seed functional connectivity analysis and graph theoretic functional brain network analysis tools, and investigated the relationship between the DMN's functional connectivity pattern of WD patients and their attention functions examined using the attention network test (ANT). Our results demonstrated that WD patients had altered DMN's functional connectivity and lower local and global network efficiency compared with normal controls (NCs). In addition, the functional connectivity between left inferior temporal cortex and right lateral parietal cortex was correlated with altering function, one of the attention functions, across WD and NC subjects. These findings indicated that the DMN's functional connectivity was altered in WD patients, which might be correlated with their attention dysfunction.

Dual Task Performance May be a Better Measure of Cognitive Processing in Huntington's Disease than Traditional Attention Tests

BACKGROUND

Past research has found cancellation tasks to be reliable markers of cognitive decline in Huntington's disease (HD).

OBJECTIVE

The aim of this study was to extend previous findings by adopting the use of a dual task paradigm that paired cancellation and auditory tasks.

METHODS

We compared performance in 14 early stage HD participants and 14 healthy controls. HD participants were further divided into groups with and without cognitive impairment.

RESULTS

Results suggested that HD participants were not slower or less accurate compared with controls; however, HD participants showed greater dual task interference in terms of speed. In addition, HD participants with cognitive impairment were slower and less accurate than HD participants with no cognitive impairment, and showed greater dual task interference in terms of speed and accuracy.

CONCLUSIONS

Our findings suggest that dual task measures may be a better measure of cognitive processing in HD compared with more traditional measures.

Selective impairment of attentional networks of alerting in Wilson's disease

Wilson's disease (WD) is typically affected by attention, which is one of the cognitive domains. The Attention Network Test (ANT) was developed to measure the functioning of the following three individual attentional networks: orienting, alerting, and executive control. The ANT has been used in a variety of neuropsychiatric conditions; however, it has not been used in WD. The aim of this study was to investigate the attentional function of WD patients, and 35 patients with early and moderate neurological WD, as well as 35 gender-, age-, and education-matched healthy controls performed the ANT. Remarkable differences between the patients and healthy controls were observed in the alerting network (p = 0.007) in contrast the differences in the orienting (p = 0.729) and executive control (p = 0.888) networks of visual attention. The mean reaction time in the ANT was significantly longer in the WD patients than in the controls (p<0.001, 0.001). In the WD patients, there was an effect specifically on the alerting domain of the attention network, whereas the orienting and executive control domains were not affected.

Frontal cortex BOLD signal changes in premanifest Huntington disease: a possible fMRI biomarker

OBJECTIVE

To identify a possible functional imaging biomarker sensitive to the earliest neural changes in premanifest Huntington disease (preHD), allowing early therapeutic approaches aimed at preventing or delaying clinical onset.

METHODS

Sixteen preHD and 18 healthy participants were submitted to anatomical acquisitions and functional MRI (fMRI) acquisitions during the execution of the exogenous covert orienting of attention task. Due to strong a priori hypothesis, all fMRI correlation analyses were restricted to the following: (1) the frontal oculomotor cortex identified by the means of a prosaccadic task, comprising frontal eye fields and supplementary frontal eye fields; and (2) the data collected during inhibition of return, a phenomenon occurring during the executed task. In preHD, multiple regression analysis was performed between fMRI data and the probability to develop the disease in the next 5 years (p5HD). Moreover, mean blood oxygen level-dependent (BOLD) signal changes in the frontal oculomotor cortex and striatal volumes were linearly correlated with p5HD.

RESULTS

In preHD, multiple regression analysis showed that clusters of activity strongly correlated with p5HD in the right frontal oculomotor cortex. Importantly, mean BOLD signal changes of this region correlated with p5HD (r(2) = 0.52). Among the considered striatal volumes, a modest correlation (r(2) = 0.29) was observed in the right putamen and p5HD.

CONCLUSION

fMRI activations in the right-frontal oculomotor cortex during inhibition of return can be considered a possible functional imaging biomarker in preHD.

Searching for inhibition of return in the rat using the covert orienting of attention task

Inhibition of return (IOR) is an important psychological construct describing inhibited responses to previously attended locations. In humans, it is investigated using Posner's cueing paradigm. This paradigm requires central visual fixation and detection of cued stimuli to the left or right of the fixation point. Stimuli can be validly or invalidly cued, appearing in the same or opposite location to the cue. Although a rat version of the spatial cueing paradigm (the covert orienting of attention task) does exist, IOR has so far not been demonstrated. We therefore investigated whether IOR could be robustly demonstrated in adult male rats using the covert orienting of attention task. This task is conducted in holed wall operant chambers with the central three holes mimicking the set-up for Posner cueing. Across four samples of rats (overall n = 84), we manipulated the following task parameters: stimulus onset asynchronies (Experiments 1-3), cue brightness (Experiment 1b) and the presence of a central reorienting event (Experiment 4). In Experiment 1, we also investigated strain differences by comparing Lister Hooded rats to Sprague-Dawley rats. Although Lister Hooded rats briefly showed evidence of IOR (Experiment 1a, and see Online Resource 1 data), we were unable to replicate this finding in our other experiments using different samples of this strain. Taken together, our findings suggest that IOR cannot be robustly demonstrated in the rat using the covert orienting of attention task conducted in holed wall operant chambers.

Deficits in selective attention in symptomatic Huntington disease: assessment using an attentional blink paradigm

BACKGROUND

Impaired selective attention in Huntington disease (HD) may manifest as difficulty in identifying a single target embedded among a series of distractors in rapid serial visual presentation tasks.

METHOD

We used an attentional blink (AB) paradigm to examine whether attentional control is impaired in symptomatic HD. Fourteen HD patients and 13 age-matched healthy controls performed a rapid serial visual presentation task in which 2 targets (T1 and T2) and numerous distractors were presented in rapid succession. We assessed the accuracy of T1 identification and the AB (impaired T2 detection after the correct identification of T1).

RESULTS

Among the HD patients, identification of T1 was significantly impaired and AB was significantly larger but not longer. The HD patients also made significantly more random errors.

CONCLUSIONS

Frontostriatal or frontoparietal dysfunction is likely to compromise attentional control in HD, such that well-masked and rapidly presented target stimuli are difficult to detect and identify, especially as the difficulty level increases. Although we previously reported no AB deficits in presymptomatic HD, with manifest disease we found that the progressive frontoparietal cortical changes compromise attentional control mechanisms.

Deficient sustained attention to response task and P300 characteristics in early Huntington's disease

Evidence for the extent and nature of attentional impairment in premanifest and manifest Huntington’s disease (HD) is inconsistent. Understanding such impairments may help to better understand early functional changes in HD and could have consequences concerning care for HD patients. We investigated attentional control in both early and premanifest HD. We studied 17 early HD subjects (mean age: 51 years), 12 premanifest HD subjects (mean age: 43 years), and 15 healthy controls (mean age: 51 years), using the sustained attention to response task (SART), a simple Go/No-go test reflecting attentional and inhibitory processes through reaction time (RT) and error rates. Simultaneously recorded EEG yielded P300 amplitudes and latencies. The early HD group made more Go errors (p < 0.001) and reacted slower (p < 0.005) than the other groups. The RT pattern during the SART was remarkably different for early HD subjects compared to the other two groups (p < 0.005), apparent as significant post-error slowing. P300 data showed that for early HD the No-go amplitude was lower than for the other two groups (p < 0.05). Subjects with early HD showed a reduced capacity to effectively control attention. They proved unable to resume the task directly after having made an error, and need more time to return to pre-error performance levels. No attentional control deficits were found for the premanifest HD group.

Five choice serial reaction time performance in the HdhQ92 mouse model of Huntington's disease

Huntington's disease is an autosomal dominant genetic disorder, with motor, cognitive and psychiatric symptoms. To date there is no cure. In order to understand better this disease and to develop novel treatments, many genetically modified animal models of Huntington's disease have been created. However, to utilize these models fully, appropriate functional assays need to be developed for behavioural assessments of the mice. Various facets of attention have been reported to be affected in Huntington's disease patients, and the Hdh(Q92/Q92) mice have been shown to have deficits on operant tasks which have attentional components. In the present study, the Hdh(Q92/Q92) mouse model is assessed on a well established test of attentional function, the operant 5-choice serial reaction time task (5-CSRT), in which the mice must respond with a nose poke to light stimuli presented randomly across a 5 hole light array to receive a reward. In the present paper, the Hdh(Q92/Q92) mice exhibited deficits on the 5-CSRT when pseudorandomly presented with stimuli of different durations. However, alterations in the pacing of the task, therefore requiring an increase in sustained attention, did not affect the Hdh(Q92/Q92) mice more than their wildtype littermates. This study indicates that the Hdh(Q92/Q92) mice may have deficits in aspects of attentional function, in particular disruption in the ability to maintain attention in the visuospatial domain, suggesting that this knock-in mouse model of Huntington's disease may be a relevant model of the disease for the testing of novel therapeutic interventions.

Longitudinal analyses of operant performance on the serial implicit learning task (SILT) in the YAC128 Huntington's disease mouse line

Huntington's disease is a genetic disorder characterised by progressive striatal and cortical neurodegeneration, resulting in a broad range of motor, cognitive and behavioural abnormalities. The disease is caused by a single mutation in the gene responsible for the protein huntingtin, increasing the number of polyQ repeats and conferring a toxic gain of function to the mutant protein, which ultimately induces cell death. Several mouse models of HD are available. The YAC128 mouse model carries 128 CAG repeats and is known to develop several HD-like symptoms. This model has been well characterised on the FVB/N background strain, a strain that develops severe retinal degeneration. We have therefore sought to characterise YAC128 deficit in mice backcrossed onto the C57BL/6j background strain which is free of visual deficits and therefore more amenable to behavioural testing. In a parallel study (this special issue) we have provided a longitudinal characterisation of the emergence of a motor phenotype in the YAC128/C57BL mice. In the present paper, we have undertaken a more detailed characterisation of cognitive impairment in this mouse line at 6, 12, and 18 months of age using the operant serial implicit learning task (SILT), a task that was first designed to assess impairments in mice similar to the implicit serial learning impairments in HD patients task, and which has subsequently been shown to be highly sensitive to cortico-striatal disruption in mice. On the SILT task, the mouse must attain rewards by correctly nose-poking to 2 stimulus lights (S1 and S2) presented randomly and sequentially in 5 holes (deemed A-E) on a light array. Performance is measured by accuracy and speed of response to the S1 and S2 stimuli. Embedded within the random sequences, was a predictable sequence whereby an S1 in hole B is always followed by the S2 in hole D, which constitutes an implicit learning probe. The YAC128 carriers were less accurate in their responses to both S1 and S2 stimuli in the absence of response latency deficits. The deficits in accuracy to the S2 stimuli were present from 6 months of age and were progressive. There was no difference between the wildtype and the YAC128 carriers in the benefits gained from identifying the predictable B-D sequence. The results suggest that the YAC128 mice have a motor-learning deficit that may reflect impulsive responding and/or impaired visuo-spatial attention consistent with a model of HD.

Spatially distributed encoding of covert attentional shifts in human thalamus

Spatial attention modulates signal processing within visual nuclei of the thalamus—but do other nuclei govern the locus of attention in top-down mode? We examined functional MRI (fMRI) data from three subjects performing a task requiring covert attention to 1 of 16 positions in a circular array. Target position was cued after stimulus offset, requiring subjects to perform target detection from iconic visual memory. We found positionally specific responses at multiple thalamic sites, with individual voxels activating at more than one direction of attentional shift. Voxel clusters at anatomically equivalent sites across subjects revealed a broad range of directional tuning at each site, with little sign of contralateral bias. By reference to a thalamic atlas, we identified the nuclear correspondence of the four most reliably activated sites across subjects: mediodorsal/central-intralaminar (oculomotor thalamus), caudal intralaminar/parafascicular, suprageniculate/limitans, and medial pulvinar/lateral posterior. Hence, the cortical network generating a top-down control signal for relocating attention acts in concert with a spatially selective thalamic apparatus—the set of active nuclei mirroring the thalamic territory of cortical “eye-field” areas, thus supporting theories which propose the visuomotor origins of covert attentional selection.

Dopaminergic Control of Attentional Flexibility: Inhibition of Return is Associated with the Dopamine Transporter Gene (DAT1)

Genetic variability related to the dopamine (DA) transporter gene (DAT1) has received increasing attention as a possible modulator of human cognition. The 9-repeat allele of the DAT1 gene is presumably associated with higher striatal DA levels than the 10-repeat allele, which might support inhibitory control functions. We investigated the impact of the DAT1 gene on the inhibition of return (IOR) effect, which refers to the fact that people are slower to detect a target if it appears in a previously attended location. 140 healthy adults, genotyped for the DAT1 gene, performed an IOR task with stimulus-onset asynchronies (SOAs) between attention cue and target of 150–1200 ms. Nine-repeat carriers showed more pronounced IOR effect than 10/10 homozygous at short SOAs but both groups of subjects eventually reached the same magnitude of IOR. Our findings support the idea that striatal DA levels promote IOR, presumably by biasing the interplay between prefrontal and striatal networks towards greater cognitive flexibility.

Neurophysiological mechanisms involved in language learning in adults

Little is known about the brain mechanisms involved in word learning during infancy and in second language acquisition and about the way these new words become stable representations that sustain language processing. In several studies we have adopted the human simulation perspective, studying the effects of brain-lesions and combining different neuroimaging techniques such as event-related potentials and functional magnetic resonance imaging in order to examine the language learning (LL) process. In the present article, we review this evidence focusing on how different brain signatures relate to (i) the extraction of words from speech, (ii) the discovery of their embedded grammatical structure, and (iii) how meaning derived from verbal contexts can inform us about the cognitive mechanisms underlying the learning process. We compile these findings and frame them into an integrative neurophysiological model that tries to delineate the major neural networks that might be involved in the initial stages of LL. Finally, we propose that LL simulations can help us to understand natural language processing and how the recovery from language disorders in infants and adults can be accomplished.

Striatal degeneration impairs language learning: evidence from Huntington's disease

Although the role of the striatum in language processing is still largely unclear, a number of recent proposals have outlined its specific contribution. Different studies report evidence converging to a picture where the striatum may be involved in those aspects of rule-application requiring non-automatized behaviour. This is the main characteristic of the earliest phases of language acquisition that require the online detection of distant dependencies and the creation of syntactic categories by means of rule learning. Learning of sequences and categorization processes in non-language domains has been known to require striatal recruitment. Thus, we hypothesized that the striatum should play a prominent role in the extraction of rules in learning a language. We studied 13 pre-symptomatic gene-carriers and 22 early stage patients of Huntington's disease (pre-HD), both characterized by a progressive degeneration of the striatum and 21 late stage patients Huntington's disease (18 stage II, two stage III and one stage IV) where cortical degeneration accompanies striatal degeneration. When presented with a simplified artificial language where words and rules could be extracted, early stage Huntington's disease patients (stage I) were impaired in the learning test, demonstrating a greater impairment in rule than word learning compared to the 20 age- and education-matched controls. Huntington's disease patients at later stages were impaired both on word and rule learning. While spared in their overall performance, gene-carriers having learned a set of abstract artificial language rules were then impaired in the transfer of those rules to similar artificial language structures. The correlation analyses among several neuropsychological tests assessing executive function showed that rule learning correlated with tests requiring working memory and attentional control, while word learning correlated with a test involving episodic memory. These learning impairments significantly correlated with the bicaudate ratio. The overall results support striatal involvement in rule extraction from speech and suggest that language acquisition requires several aspects of memory and executive functions for word and rule learning.