Left handers are less lateralized than right handers for both left and right hemispheric functions

Many neuroscientific techniques have revealed that more left- than right-handers will have unusual cerebral asymmetries for language. After the original emphasis on frequency in the aphasia and epilepsy literatures, most neuropsychology, and neuroimaging efforts rely on estimates of central tendency to compare these two handedness groups on any given measure of asymmetry. The inevitable reduction in mean lateralization in the left-handed group is often postulated as being due to reversed asymmetry in a small subset of them, but it could also be due to a reduced asymmetry in many of the left-handers. These two possibilities have hugely different theoretical interpretations. Using functional magnetic resonance imaging localizer paradigms, we matched left- and right-handers for hemispheric dominance across four functions (verbal fluency, face perception, body perception, and scene perception). We then compared the degree of dominance between the two handedness groups for each of these four measures, conducting t-tests on the mean laterality indices. The results demonstrate that left-handers with typical cerebral asymmetries are less lateralized for language, faces, and bodies than their right-handed counterparts. These results are difficult to reconcile with current theories of language asymmetry or of handedness

Towards a unified understanding of lateralized vision:A large-scale study investigating principles governing patterns of lateralization using a heterogeneous sample

While functional lateralization of the human brain has been a widely studied topic in the past decades, few studies to date have gone further than investigating lateralization of single, isolated processes. With the present study, we aimed to arrive at a more unified view by investigating lateralization patterns in face and word processing, and associated lower-level visual processing. We tested a large and heterogeneous participant group, and used a number of tasks that had been shown to produce replicable indices of lateralized processing of visual information of different types and complexity. Following Bayesian statistics, group-level analyses showed the expected right hemisphere (RH) lateralization for face, global form, low spatial frequency processing, and spatial attention, and left hemisphere (LH) lateralization for visual word and local feature processing. Compared to right-handed individuals, lateralization patterns of left-handed and especially those who are RH-dominant for language deviated from this 'typical' pattern. Our results support the notion that face and word processes come to be lateralized to homologue areas of the two hemispheres, under influence of the RHand LH-specializations in global form, local feature, and low and high spatial frequency processing. As such, we present a more unified understanding of lateralized vision, providing evidence for the input asymmetry and causal complementarity principles of lateralized visual information processing. The absence of correlations between spatial attention and lateralization of the other processes supports the notion of their independent lateralization, conform the statistical complementarity principle. (C) 2020 The Author(s). Published by Elsevier Ltd

Unique N170 Signatures to Words and Faces in Deaf ASL Signers Reflect Experience-Specific Adaptations During Early Visual Processing

Previous studies with deaf adults reported reduced N170 waveform asymmetry to visual words, a finding attributed to reduced phonological mapping in left-hemisphere temporal regions compared to hearing adults. An open question remains whether this pattern indeed results from reduced phonological processing or from general neurobiological adaptations in visual processing of deaf individuals. Deaf ASL signers and hearing nonsigners performed a same-different discrimination task with visually presented words, faces, or cars, while scalp EEG time-locked to the onset of the first item in each pair was recorded. For word recognition, the typical left-lateralized N170 in hearing participants and reduced left-sided asymmetry in deaf participants were replicated. The groups did not differ on word discrimination but better orthographic skill was associated with larger N170 in the right hemisphere only for deaf participants. Face recognition was characterized by unique N170 signatures for both groups, and deaf individuals exhibited superior face discrimination performance. Laterality or discrimination performance effects did not generalize to the N170 responses to cars, confirming that deaf signers are not inherently less lateralized in their electrophysiological responses to words and critically, giving support to the phonological mapping hypothesis. P1 was attenuated for deaf participants compared to the hearing, but in both groups, P1 selectively discriminated between highly learned familiar objects – words and faces versus less familiar objects – cars. The distinct electrophysiological signatures to words and faces reflected experience-driven adaptations to words and faces that do not generalize to object recognition

The relationship between behavioral language laterality, face laterality and language performance in left-handers

Left-handers provide unique information about the relationship between cognitive functions because of their larger variability in hemispheric dominance. This study presents the laterality distribution of, correlations between and test-retest reliability of behavioral lateralized language tasks (speech production, reading and speech perception), face recognition tasks, handedness measures and language performance tests based on data from 98 left-handers. The results show that a behavioral test battery leads to percentages of (a) typical dominance that are similar to those found in neuropsychological studies even though the incidence of clear atypical lateralization (about 20%) may be overestimated at the group level. Significant correlations were found between the language tasks for both reaction time and accuracy lateralization indices. The degree of language laterality could however not be linked to face laterality, handedness or language performance. Finally, individuals were classified less consistently than expected as being typical, bilateral or atypical across all tasks. This may be due to the often good (speech production and perception tasks) but sometimes weak (reading and face tasks) test-retest reliabilities. The lack of highly reliable and valid test protocols for functions unrelated to speech remains one of the largest impediments for individual analysis and cross-task investigations in laterality research

Neural Correlates of Automatic Emotional Processing and Emotion Regulation in Empathy and Psychopathy-Related Coldheartedness

Psychopathy is a personality disorder that is defined, in part, by a lack of empathy. Psychopathy-related empathic deficits have been associated with atypical behavioral and neural responses to emotional facial expressions. Although the mirror neuron system (MNS) has been implicated in empathy, very few studies have examined the role of MNS functioning as it pertains to empathy impairments in psychopathy. Moreover, there is very little empirical research regarding emotion regulation in psychopathy, and specifically whether emotional responses can be intentionally upregulated. The present study sought to clarify whether the MNS is functionally intact in adults with subclinical psychopathic traits, particularly Coldheartedness, and whether the MNS can be manipulated through top-down mechanisms. Five hundred six undergraduates completed the Psychopathic Personality Inventory-Revised to measure psychopathic traits and the Interpersonal Reactivity Index to measure empathic traits. Of these, 60 eligible participants then completed an EEG/ERP study. Participants first passively viewed images of emotional faces (Task 1), and then tried to increase their emotional response to the same pictures (Task 2) while their EEG was recorded. Bottom-up functioning was indexed by mu rhythm (8-12 Hz) desynchronization, a measure of MNS function. In addition, the amplitude of the P100, N170, and Late Positive Potential (LPP) event-related potentials were used to measure attentional processes, with later components reflecting more top-down processing. The change in each of these measurements from Task 1 to Task 2 was used to index upregulation. Contrary to our predictions, we found that Coldheartedness was not related to mu rhythm suppression or upregulation, suggesting that mirror neuron system functioning was intact. Moreover, Coldheartedness predicted larger N170 and LPP (400-600 ms) amplitudes in Task 1, indicating increased early attention to the emotional faces. Empathy, on the other hand, was related to reduced automatic attentional processing, evidenced by less mu suppression (i.e., less MNS activity), and smaller early ERP components, but greater sustained attention (as evidenced by higher amplitude LPPs), and an enhanced ability to upregulate ERP markers of early attention (i.e., N170). Together, these results provide a new perspective on the neural correlates of empathic functioning in subclinical psychopathy

A unified view of lateralized vision

Left for the trees, right for the forestThe fact that humans have two brain halves, each with their own specialization, speaks to the imagination. The left ‘language’ brain is commonly known example of brain specialization. Sanne Brederoo, researcher at the RUG, shows that the two brain halves are also strongly specialized for vision.During the past 50 years, many studies were carried out to investigate the specialization of the two brain halves. With her dissertation, Brederoo shows that a number of such so-called specializations are in fact myths. Does this mean that the two halves of the brain perform the exact same tasks? Not quite, as that would be a waste of space. Brederoo convincingly shows that both halves –each with their own specializations– are involved in vision. The left halve is an expert in processing detail and reading words. (Not unexpected, given that words consist of letters: many small details.) The right halve is specialized in seeing the bigger picture and viewing faces. (Again quite understandable, given that we usually view faces as a whole, rather than looking at the nose, lips, or eyes individually.) In sum; both brain halves are active during everyday vision, each with their own specialization.In addition, Brederoo shares a remarkable finding: during the viewing of faces, a number of left-handed people use more of both brain halves instead of just the right one.So … when you’re unable to see the forest for the trees, your left brain is working too hard. Then you’d better address your right brain in order to see the bigger picture again

Neurophysiological assessments of low-level and high-level interdependencies between auditory and visual systems in the human brain

This dissertation investigates the functional interplay between visual and auditory systems and its degree of experience-dependent plasticity. To function efficiently in everyday life, we must rely on our senses, building complex hierarchical representations about the environment. Early sensory deprivation, congenital (from birth) or within the first year of life, is a key model to study sensory experience and the degree of compensatory reorganizations (i.e., neuroplasticity). Neuroplasticity can be intramodal (within the sensory system) and crossmodal (the recruitment of deprived cortical areas for remaining senses). However, the exact role of early sensory experience and the mechanisms guiding experience-driven plasticity need further investigation. To this aim, we performed three electroencephalographic studies, considering the aspects: 1) sensory modality (auditory/visual), 2) hierarchy of the brain functional organization (low-/high-level), and 3)sensory deprivation (deprived/non-deprived cortices). The first study explored how early auditory experience affects low-level visual processing, using time-frequency analysis on the data of early deaf individuals and their hearing counterparts. The second study investigated experience- dependent plasticity in hierarchically organized face processing, applying fast periodic visual stimulation in congenitally deaf signers and their hearing controls. The third study assessed neural responses of blindfolded participants, using naturalistic stimuli together with temporal response function, and evaluated neural tracking in hierarchically organized speech processing when retinal input is absent, focusing on the role of the visual cortex. The results demonstrate the importance of atypical early sensory experience in shaping (via intra-and crossmodal changes) the brain organization at various hierarchical stages of sensory processing but also support the idea that some crossmodal effects emerge even with typical experience. This dissertation provides new insights into understanding the functional interplay between visual and auditory systems and the related mechanisms driving experience-dependent plasticity and may contribute to the development of sensory restoration tools and rehabilitation strategies for sensory-typical and sensory-deprived populations