Anjali Raja Beharelle

Left hemisphere regions are critical for language in the face of early left focal brain injury

A predominant theory regarding early stroke and its effect on language development, is that early left hemisphere lesions trigger compensatory processes that allow the right hemisphere to assume dominant language functions, and this is thought to underlie the near normal language development observed after early stroke. To test this theory, we used functional magnetic resonance imaging to examine brain activity during category fluency in participants who had sustained pre- or perinatal left hemisphere stroke (n = 25) and in neurologically normal siblings (n = 27). In typically developing children, performance of a category fluency task elicits strong involvement of left frontal and lateral temporal regions and a lesser involvement of right hemisphere structures. In our cohort of atypically developing participants with early stroke, expressive and receptive language skills correlated with activity in the same left inferior frontal regions that support language processing in neurologically normal children. This was true independent of either the amount of brain injury or the extent that the injury was located in classical cortical language processing areas. Participants with bilateral activation in left and right superior temporal-inferior parietal regions had better language function than those with either predominantly left- or right-sided unilateral activation. The advantage conferred by left inferior frontal and bilateral temporal involvement demonstrated in our study supports a strong predisposition for typical neural language organization, despite an intervening injury, and argues against models suggesting that the right hemisphere fully accommodates language function following early injury.

Brain signal variability relates to stability of behavior after recovery from diffuse brain injury

Variability or noise is an unmistakable feature of neural signals; however such fluctuations have been regarded as not carrying meaningful information or as detrimental for neural processes. Recent empirical and computational work has shown that neural systems with a greater capacity for information processing are able to explore a more varied dynamic repertoire, and the hallmark of this is increased irregularity or variability in the neural signal. How this variability in neural dynamics affects behavior remains unclear. Here, we investigated the role of variability of magnetoencephalography signals in supporting healthy cognitive functioning, measured by performance on an attention task, in healthy adults and in patients with traumatic brain injury. As an index of variability, we calculated multiscale entropy, which quantifies the temporal predictability of a time series across progressively more coarse time scales. We found lower variability in traumatic brain injury patients compared to controls, arguing against the idea that greater variability reflects dysfunctional neural processing. Furthermore, higher brain signal variability indicated improved behavioral performance for all participants. This relationship was statistically stronger for people with brain injury, demonstrating that those with higher brain signal variability were also those who had recovered the most cognitive ability. Rather than impede neural processing, cortical signal variability within an optimal range enables the exploration of diverse functional configurations, and may therefore play a vital role in healthy brain function.

Interhemispheric Functional Connectivity following Prenatal or Perinatal Brain Injury Predicts Receptive Language Outcome

Early brain injury alters both structural and functional connectivity between the cerebral hemispheres. Despite increasing knowledge on the individual hemispheric contributions to recovery from such injury, we know very little about how their interactions affect this process. In the present study, we related interhemispheric structural and functional connectivity to receptive language outcome following early left hemisphere stroke. We used functional magnetic resonance imaging to study 14 people with neonatal brain injury, and 25 age-matched controls during passive story comprehension. With respect to structural connectivity, we found that increased volume of the corpus callosum predicted good receptive language outcome, but that this is not specific to people with injury. In contrast, we found that increased posterior superior temporal gyrus interhemispheric functional connectivity during story comprehension predicted better receptive language performance in people with early brain injury, but worse performance in typical controls. This suggests that interhemispheric functional connectivity is one potential compensatory mechanism following early injury. Further, this pattern of results suggests refinement of the prevailing notion that better language outcome following early left hemisphere injury relies on the contribution of the contralesional hemisphere (i.e., the “right-hemisphere-take-over” theory). This pattern of results was also regionally specific; connectivity of the angular gyrus predicted poorer performance in both groups, independent of brain injury. These results present a complex picture of recovery, and in some cases, such recovery relies on increased cooperation between the injured hemisphere and homologous regions in the contralesional hemisphere, but in other cases, the opposite appears to hold.

Computational Modeling of Resting-State Activity Demonstrates Markers of Normalcy in Children with Prenatal or Perinatal Stroke

Children who sustain a prenatal or perinatal brain injury in the form of a stroke develop remarkably normal cognitive functions in certain areas, with a particular strength in language skills. A dominant explanation for this is that brain regions from the contralesional hemisphere “take over” their functions, whereas the damaged areas and other ipsilesional regions play much less of a role. However, it is difficult to tease apart whether changes in neural activity after early brain injury are due to damage caused by the lesion or by processes related to postinjury reorganization. We sought to differentiate between these two causes by investigating the functional connectivity (FC) of brain areas during the resting state in human children with early brain injury using a computational model. We simulated a large-scale network consisting of realistic models of local brain areas coupled through anatomical connectivity information of healthy and injured participants. We then compared the resulting simulated FC values of healthy and injured participants with the empirical ones. We found that the empirical connectivity values, especially of the damaged areas, correlated better with simulated values of a healthy brain than those of an injured brain. This result indicates that the structural damage caused by an early brain injury is unlikely to have an adverse and sustained impact on the functional connections, albeit during the resting state, of damaged areas. Therefore, these areas could continue to play a role in the development of near-normal function in certain domains such as language in these children.

Brain Activity Patterns Uniquely Supporting Visual Feature Integration after Traumatic Brain Injury

Traumatic brain injury (TBI) patients typically respond more slowly and with more variability than controls during tasks of attention requiring speeded reaction time. These behavioral changes are attributable, at least in part, to diffuse axonal injury (DAI), which affects integrated processing in distributed systems. Here we use a multivariate method sensitive to distributed neural activity to compare brain activity patterns of patients with chronic phase moderate to-severe TBI to those of controls during performance on a visual feature integration task assessing complex attentional processes that has previously shown sensitivity to TBI. The TBI patients were carefully screened to be free of large focal lesions that can affect performance and brain activation independently of DAI. The task required subjects to hold either one or three features of a Target in mind while suppressing responses to distracting information. In controls, the multi-feature condition activated a distributed network including limbic, prefrontal, and medial temporal structures. TBI patients engaged this same network in the single-feature and baseline conditions. In multi-feature presentations, TBI patients alone activated additional frontal, parietal, and occipital regions. These results are consistent with neuroimaging studies using tasks assessing different cognitive domains, where increased spread of brain activity changes was associated with TBI. Our results also extend previous findings that brain activity for relatively moderate task demands in TBI patients is similar to that associated with of high task demands in controls.

The dopaminergic reward system underpins gender differences in social preferences

Women are known to have stronger prosocial preferences than men, but it remains an open question as to how these behavioural differences arise from differences in brain functioning. Here, we provide a neurobiological account for the hypothesized gender difference. In a pharmacological study and an independent neuroimaging study, we tested the hypothesis that the neural reward system encodes the value of sharing money with others more strongly in women than in men. In the pharmacological study, we reduced receptor type-specific actions of dopamine, a neurotransmitter related to reward processing, which resulted in more selfish decisions in women and more prosocial decisions in men. Converging findings from an independent neuroimaging study revealed gender-related activity in neural reward circuits during prosocial decisions. Thus, the neural reward system appears to be more sensitive to prosocial rewards in women than in men, providing a neurobiological account for why women often behave more prosocially than men.Women often behave more prosocially than men. Soutschek et al. use pharmacology and neuroimaging to show that the neural reward system appears to be more sensitive to prosocial rewards in women than men, providing a neurobiological account for this gender difference.

Perinatal focal brain injury: scope and limits of plasticity for language functions

Children with perinatal focal brain injury exhibit normal or near-normal language development even when lesions are large and encompass classic left hemisphere perisylvian language networks. Their language difficulties are much more subtle than those seen in adults with similar lesions. We review the literature on the effects of perinatal injury on language development, with a focus on the scope and limits of functional plasticity, the relation between biological characteristics of lesions and language input on functional plasticity, and potential mechanisms of language plasticity after early lesions. The literature on the plasticity for language functions after perinatal focal brain injury presents a challenge to theories that posit an immutable brain basis for language and is consistent with the view of a dynamic, plastic brain—a developing brain capable of responding to internal biological signals, including those associated with injury, and to information provided by the environment.Children with perinatal focal brain injury exhibit normal or near-normal language development even when lesions are large and encompass classic left hemisphere perisylvian language networks. Their language difficulties are much more subtle than those seen in adults with similar lesions. We review the literature on the effects of perinatal injury on language development, with a focus on the scope and limits of functional plasticity, the relation between biological characteristics of lesions and language input on functional plasticity, and potential mechanisms of language plasticity after early lesions. The literature on the plasticity for language functions after perinatal focal brain injury presents a challenge to theories that posit an immutable brain basis for language and is consistent with the view of a dynamic, plastic brain—a developing brain capable of responding to internal biological signals, including those associated with injury, and to information provided by the environment.

Dopamine receptor-specific contributions to the computation of value

Dopamine is thought to play a crucial role in value-based decision making. However, the specific contributions of different dopamine receptor subtypes to the computation of subjective value remain unknown. Here we demonstrate how the balance between D1 and D2 dopamine receptor subtypes shapes subjective value computation during risky decision making. We administered the D2 receptor antagonist amisulpride or placebo before participants made choices between risky options. Compared with placebo, D2 receptor blockade resulted in more frequent choice of higher risk and higher expected value options. Using a novel model fitting procedure, we concurrently estimated the three parameters that define individual risk attitude according to an influential theoretical account of risky decision making (prospect theory). This analysis revealed that the observed reduction in risk aversion under amisulpride was driven by increased sensitivity to reward magnitude and decreased distortion of outcome probability, resulting in more linear value coding. Our data suggest that different components that govern individual risk attitude are under dopaminergic control, such that D2 receptor blockade facilitates risk taking and expected value processing.

Dissociable mechanisms govern when and how strongly reward attributes affect decisions

Theories and computational models of decision making usually focus on how strongly different attributes are weighted in choice, e.g., as a function of their importance or salience to the decision-maker. However, when different attributes impact on the decision process is a question that has received far less attention. Here, we investigated whether attribute consideration timing has a unique influence on decision making using a time-varying drift diffusion model and data from four separate experiments. Experimental manipulations of attention and neural activity demonstrated that we can dissociate the processes that determine the relative weighting strength and timing of attribute consideration. Thus, the processes determining either the weighting strengths or the timing of attributes in decision making can adapt independently to changes in the environment or goals. Quantifying these separate influences of timing and weighting on choice improves our understanding and predictions of individual differences in decision behaviour.

Imaging Brain Networks for Language: Methodology and Examples from the Neurobiology of Reading

Studying the neurobiology of language has begun to shift away from investigating individual regions in the brain to understanding how interactions among these regions bring about language functions. Here, we review common multivariate analysis techniques for neuroimaging data that have been used to investigate the brain networks underlying reading. For each technique, we describe the method as well as its advantages compared to other methods. We then provide examples showing how the technique has been used to understand better the functional neural architecture supporting reading.Studying the neurobiology of language has begun to shift away from investigating individual regions in the brain to understanding how interactions among these regions bring about language functions. Here, we review common multivariate analysis techniques for neuroimaging data that have been used to investigate the brain networks underlying reading. For each technique, we describe the method as well as its advantages compared to other methods. We then provide examples showing how the technique has been used to understand better the functional neural architecture supporting reading.