Single-case cognitive neuropsychology in the age of big data

Neurocognitive Assessment of Mathematics-Related Capacities in Neurosurgical Patients

A precise neuropsychological assessment is of the utmost importance for neurosurgical patients undergoing the surgical excision of cerebral lesions. The assessment of mathematical abilities is usually limited to arithmetical operations while other fundamental visuo-spatial aspects closely linked to mathematics proficiency, such as the perception of numerical quantities and geometrical reasoning, are completely neglected. We evaluated these abilities with two objective and reproducible psychophysical tests, measuring numerosity perception and non-symbolic geometry, respectively. We tested sixteen neuro-oncological patients before the operation and six after the operation with classical neuropsychological tests and with two psychophysical tests. The scores of the classical neuropsychological tests were very heterogeneous, possibly due to the distinct location and histology of the tumors that might have spared (or not) brain areas subserving these abilities or allowed for plastic reorganization. Performance in the two non-symbolic tests reflected, on average, the presumed functional role of the lesioned areas, with participants with parietal and frontal lesions performing worse on these tests than patients with occipital and temporal lesions. Single-case analyses not only revealed some interesting exceptions to the group-level results (e.g., patients with parietal lesions performing well in the numerosity test), but also indicated that performance in the two tests was independent of non-verbal reasoning and visuo-spatial working memory. Our results highlight the importance of assessing non-symbolic numerical and geometrical abilities to complement typical neuropsychological batteries. However, they also suggest an avoidance of reliance on an excessively rigid localizationist approach when evaluating the neuropsychological profile of oncological patients.

The longitudinal trajectory of discourse from the hyperacute to the chronic phase in mild to moderate poststroke aphasia recovery: A case series study

BACKGROUND

Discourse analysis has recently received much attention in the aphasia literature. Even if post-stroke language recovery occurs throughout the longitudinal continuum of recovery, very few studies have documented discourse changes from the hyperacute to the chronic phases of recovery.

AIMS

To document a multilevel analysis of discourse changes from the hyperacute phase to the chronic phase of post-stroke recovery using a series of single cases study designs.

METHODS & PROCEDURES

Four people with mild to moderate post-stroke aphasia underwent four assessments (hyperacute: 0-24 h; acute: 24-72 h; subacute: 7-14 days; and chronic: 6-12 months post-onset). Three discourse tasks were performed at each time point: a picture description, a personal narrative and a story retelling. Multilevel changes in terms of macro- and microstructural aspects were analysed. The results of each discourse task were combined for each time point. Individual effect sizes were computed to evaluate the relative strength of changes in an early and a late recovery time frame.

OUTCOMES & RESULTS

Macrostructural results revealed improvements throughout the recovery continuum in terms of coherence and thematic efficiency. Also, the microstructural results demonstrated linguistic output improvement for three out of four participants. Namely, lexical diversity and the number of correct information units/min showed a greater gain in the early compared with the late recovery phase.

CONCLUSIONS & IMPLICATIONS

This study highlights the importance of investigating all discourse processing levels as the longitudinal changes in discourse operate differently at each phase of recovery. Overall results support future longitudinal discourse investigation in people with post-stroke aphasia.

WHAT THIS PAPER ADDS

What is already known on the subject Multi-level discourse analysis allows for in-depth analysis of underlying discourse processes. To date, very little is known on the longitudinal discourse changes from aphasia onset through to the chronic stage of recovery. This study documents multi-level discourse features in four people with mild to moderate aphasia in the hyperacute, acute, subacute and chronic stage of post-stroke aphasia recovery. What this paper adds to existing knowledge The study found that most discourse variables demonstrated improvement throughout time. Macrostructural variables of coherence and thematic units improved throughout the continuum whereas microstructural variables demonstrated greater gains in the early compared to the late period of recovery. What are the potential or actual clinical implications of this work? This study suggests that multilevel discourse analysis will allow a better understanding of post-stroke aphasia recovery, although more research is needed to determine the clinical utility of these findings. Future research may wish to investigate longitudinal discourse recovery in a larger sample of people with aphasia with heterogenous aphasia profiles and severities.

Largely intact memory for spatial locations during navigation in an individual with dense amnesia

Spatial navigation and event memory (termed episodic memory) are thought to be heavily intertwined, both in terms of their cognitive processes and underlying neural systems. Some theoretical models posit that both memory for places during navigation and episodic memory depend on highly overlapping brain systems. Here, we assessed this relationship by testing navigation in an individual with severe retrograde and anterograde amnesia; the amnesia stemmed from bilateral lesions in the medial temporal lobes from two separate strokes. The individual with amnesia and age-matched controls were tested on their memories for the locations of previously seen objects relative to distal mountain cues in an immersive virtual environment involving free ambulation. All participants were tested from both repeated and novel start locations and when a single distal mountain cue was unknowingly moved to determine if they relied on a single (beacon) cue to a greater extent than the collection of all distal cues. Compared to age-matched controls, the individual with amnesia showed no significant deficits in navigation from either the repeated or novel start points, although both the individual with amnesia and controls performed well above chance at placing objects near their correct locations. The individual with amnesia also relied on a combination of distal cues in a manner comparable to age-matched controls. Despite largely intact memory for locations using distal cues, the individual with amnesia walked longer paths, rotated more, and took longer to complete trials. Our findings suggest that memory for places during navigation and episodic memory may involve partially dissociable brain circuits and that other brain regions outside of the medial temporal lobe partially support some aspects of navigation. At the same time, the fact that the individual with amnesia walked more circuitous paths and had dense amnesia for autobiographic events supports the idea that the hippocampus may be important for binding information as part of a larger role in memory.

Dissociable language and executive control deficits and recovery in post-stroke aphasia: An exploratory observational and case series study

A growing body of evidence indicates many, but not all, individuals with post-stroke aphasia experience executive dysfunction. Relationships between language and executive function skills are often reported in the literature, but the degree of interdependence between these abilities remains largely unanswered. Therefore, in this study, we investigated the extent to which language and executive control deficits dissociated in 1) acute stroke and 2) longitudinal aphasia recovery. Twenty-three individuals admitted to Johns Hopkins Hospital with a new left hemisphere stroke completed the Western Aphasia Battery-Revised (WAB-R), several additional language measures (of naming, semantics, spontaneous speech, and oral reading), and three non-linguistic cognitive tasks from the NIH Toolbox (i.e., Pattern Comparison Processing Speed Test, Flanker Inhibitory Control and Attention Test, and Dimensional Change Card Sorting Test). Two participants with aphasia (PWA) with temporoparietal lesions, one of whom (PWA1) had greater temporal but less frontal and superior parietal damage than the other (PWA2), also completed testing at subacute (three months post-onset) and early chronic (six months post-onset) time points. In aim 1, principal component analysis on the acute test data (excluding the WAB-R) revealed language and non-linguistic executive control tasks largely loaded onto separate components. Both components were significant predictors of acute aphasia severity per the WAB-R Aphasia Quotient (AQ). Crucially, executive dysfunction explained an additional 17% of the variance in AQ beyond the explanatory power of language impairments alone. In aim 2, both case patients exhibited language and executive control deficits at the acute post-stroke stage. A dissociation was observed in longitudinal recovery of these patients. By the early chronic time point, PWA1 exhibited improved (but persistent) deficits in several language domains and recovered executive control. In contrast, PWA2 demonstrated mostly recovered language but persistent executive dysfunction. Greater damage to language and attention networks in these respective patients may explain the observed behavioral patterns. These results demonstrate that language and executive control can dissociate (at least to a degree), but both contribute to early post-stroke presentation of aphasia and likely influence longitudinal aphasia recovery.

Cerebellar contributions to orthographic working memory: A single case cognitive neuropsychological investigation

Single case cognitive neuropsychological investigations involve the precise characterization of cognitive impairment at the level of an individual participant. This deep data precision affords a more fine-grained understanding of the cognitive and neural underpinnings of complex tasks, and continues to provide unique insights that inform theory in cognitive neuroscience. Here, we present a single case study of an individual, F.R., who suffered a stroke that led to chronic reading and writing problems that include an impairment to the orthographic working memory system proposed to be involved in both written language production and comprehension. Individuals who have been previously reported with a similar cognitive impairment commonly have left parietal lesions. However, F.R.'s orthographic working memory deficit resulted from damage to the right cerebellum, specifically to a region that is both structurally and functionally connected to the left parietal lobe and has been identified as part of the spelling network in previous meta-analyses of writing fMRI studies. From this lesion-symptom association, we argue that orthographic working memory is subserved by a cortical-cerebellar circuit, with damage at any point in the circuit resulting in an impairment to this function. Such a conclusion is warranted by observations from this single case approach, and we argue that these observations would likely have been missed if F.R. had been included in a larger, shallower group study. In addition to elucidating our understanding of the neural basis of spelling, this case study demonstrates the value that single case neuropsychology can continue to bring to cognitive neuroscience.

Combined lesion-deficit and fMRI approaches in single-case studies: Unique contributions to cognitive neuroscience

Although lesion-deficit case studies are foundational in cognitive neuroscience, published papers presenting single lesion cases are declining. In this review, we argue that there is a valuable place for single-case lesion-deficit research, especially when combined with functional neuroimaging methods, such as functional magnetic resonance imaging (fMRI). To support this, we present a summary of notable findings from single-case combined lesion-deficit and fMRI studies published in recent years (2017-2020). These studies show the unique value that this combined approach brings to the understanding of complex functions, brain-level connectivity, and plasticity and recovery. We encourage researchers to consider combining lesion-deficit and functional imaging methods in the analysis of single cases, as this approach affords unique opportunities to address challenging unanswered questions about brain-behavior relationships.

Super-Recognizers - a novel diagnostic framework, 70 cases, and guidelines for future work

When you hear the word Super-Recognizer, you may think of comic-book-hero-esque agents searching the underground to find people who went missing decades ago. Compared to this fantasy, the reality seems somewhat less exciting. Super-Recognizers (SRs) were initially reported a decade ago as a collateral while developing tests for developmental prosopagnosia. Today, the topic of SRs sparks interest from groups seeking to enhance scientific knowledge, public safety, or their monetary gain. With no immediate consequences of erroneous SR identification, there has been no pressure to establish a clear SR definition. This promotes heterogenous empirical evidence and the proliferation of unsupported claims in the media. Not only is this status quo unfortunate, it stands in opposition to the potential of special populations - both for science and application. SRs are a special population with imminent real-world value that can advance our understanding of brain functioning. To exploit their potential, I propose a needed formal framework for SR diagnosis, and introduce 70 cases identified based hereupon. These cases represent the core of a growing SR cohort, studied in my lab in the course of a long-term, multi-methodological research agenda involving academic and government collaborators. Finally, I provide recommendations for those interested in SR work, and highlight current caveats and future challenges.

Neural Evidence of Superior Memory: How to Capture Brain Activities of Encoding Processes Underlying Superior Memory

Relatively little attention has been paid to the neural basis of superior memory despite its potential in providing important insight into efforts to improve memory in the general population or to offset age-related cognitive decline. The current study reports a rare opportunity to reproduce and isolate specific neural activities directly associated with exceptional memory. To capture the brain processes responsible for superior memory, we returned to a laboratory task and analytic approach used to explore the nature of exceptional memory, namely, digit-span task combined with verbal protocol analysis. One participant with average memory received approximately 50 h of digit-span training and the participant's digit-span increased from normative (8 digits) to exceptional (30 digits). Event-related potentials were recorded while the participant's digit span increased from 19 to 30 digits. Protocol analysis allowed us to identify direct behavioral indices of idiosyncratic encoding processes underlying the superior memory performance. EEG indices directly corresponding to the behavioral indices of encoding processes were identified. The results suggest that the early attention-related encoding processes were reflected in theta and delta whereas the later attention-independent encoding processes were reflected in time-domain slow-wave. This fine-grained approach offers new insights into studying neural mechanism mediating superior memory and the cognitive effort necessary to develop it.

Neuronal mechanisms of motion detection underlying blindsight assessed by functional magnetic resonance imaging (fMRI)

Brain imaging offers a valuable tool to observe functional brain plasticity by showing how sensory inputs reshape cortical activations after a visual impairment. Following a unilateral post-chiasmatic lesion affecting the visual cortex, patients may suffer a contralateral visual loss referred to homonymous hemianopia. Nevertheless, these patients preserve the ability to unconsciously detect, localize and discriminate visual stimuli presented in their impaired visual field. To investigate this paradox, known as blindsight, we conducted a study using functional magnetic resonance imaging (fMRI) to evaluate the structural and functional impact of such lesion in a 33-year old patient (ML), who suffers a complete right hemianopia without macular sparing and showing strong evidences of blindsight. We thus performed whole brain and sliced thalamic fMRI scan sequences during an event-related motion detection task. We provided evidence of the neuronal fingerprint of blindsight by acquiring and associating neural correlates, specific structures and functional networks of the midbrain during blindsight performances which may help to better understand this condition. Accurate performance demonstrated the presence of residual vision and the ability to unconsciously perceive motion presented in the blind hemifield, although her reaction time was significantly higher in her blind-field. When the normal hemifield was stimulated, we observed significant contralateral activations in primary and secondary visual areas as well as motion specific areas, such as the supramarginal gyrus and middle temporal area. We also demonstrated sub-thalamic activations within the superior colliculi (SC) and the pulvinar. These results suggest a role of secondary subcortical structures in normal spontaneous motion detection. In a similar way, when the lesioned hemifield was stimulated, we observed contralateral activity in extrastriate areas with no activation of the primary lesioned visual cortex. Moreover, we observed activations within the SC when the blind hemifield was stimulated. However, we observed unexpected ipsilateral activations within the same motion specific areas, as well as bilateral frontal activations. These results highlight the importance of abnormal secondary pathways bypassing the primary visual area (V1) in residual vision. This reorganization in the structure and function of the visual pathways correlates with behavioral changes, thus offering a plausible explanation for the blindsight phenomenon. Our results may potentially impact the development of rehabilitation strategies to target subcortical pathways.