The functional organization of skilled actions in the adextral and atypical brain.

When planning functional grasps of tools, right-handed individuals (dextrals) show mostly left-lateralized neural activity in the praxis representation network (PRN), regardless of the used hand. Here we studied whether or not similar cerebral asymmetries are evident in non-righthanded individuals (adextrals). Sixty two participants, 28 righthanders and 34 non-righthanders (21 lefthanders, 13 mixedhanders), planned functional grasps of tools vs. grasps of control objects, and subsequently performed their pantomimed executions, in an event-related functional magnetic resonance imaging (fMRI) project. Both hands were tested, separately in two different sessions, counterbalanced across participants. After accounting for non-functional components of the prospective grasp, planning functional grasps of tools was associated with greater engagement of the same, left-hemisphere occipito-temporal, parietal and frontal areas of PRN, regardless of hand and handedness. Only when the analyses involved signal changes referenced to resting baseline intervals, differences between adextrals and dextrals emerged. Whereas in the left hemisphere the neural activity was equivalent in both groups (except for the occipito-temporo-parietal junction), its increases in the right occipito-temporal cortex, medial intraparietal sulcus (area MIP), the supramarginal gyrus (area PFt/PF), and middle frontal gyrus (area p9-46v) were significantly greater in adextrals. The inverse contrast was empty. Notably, when individuals with atypical and typical hemispheric phenotypes were directly compared, planning functional (vs. control) grasps invoked, instead, significant clusters located nearly exclusively in the left hemisphere of the typical phenotype. Previous studies interpret similar right-sided vs. left-sided increases in neural activity for skilled actions as handedness dependent, i.e., located in the hemisphere dominant for manual skills. Yet, none of the effects observed here can be purely handedness dependent because there were mixed-handed individuals among adextrals, and numerous mixed-handed and left-handed individuals possess the typical phenotype. Thus, our results clearly show that hand dominance has limited power in driving the cerebral organization of motor cognitive functions.

Diagnosing homo digitalis: towards a standardized assessment for digital tool competencies.

Introduction: In the 21st century, digital devices have become integral to our daily lives. Still, practical assessments designed to evaluate an individual's digital tool competencies are absent. The present study introduces the "Digital Tools Test" ("DIGI"), specifically designed for the evaluation of one's proficiency in handling common applications and functions of smartphones and tablets. The DIGI assessment has been primarily tailored for prospective use among older adults and neurological patients with the latter frequently suffering from so-called apraxia, which potentially also affects the handling of digital tools. Similar to traditional tool use tests that assess tool-selection and tool-action processes, the DIGI assessment evaluates an individual's ability to select an appropriate application for a given task (e.g., creating a new contact), their capacity to navigate within the chosen application and their competence in executing precise and accurate movements, such as swiping. Methods: We tested the implementation of the DIGI in a group of 16 healthy adults aged 18 to 28 years and 16 healthy adults aged 60 to 74 years. All participants were able to withstand the assessment and reported good acceptance. Results: The results revealed a significant performance disparity, with older adults displaying notably lower proficiency in the DIGI. The DIGI performance of older adults exhibited a correlation with their ability to employ a set of novel mechanical tools, but not with their ability to handle a set of familiar common tools. There was no such correlation for the younger group. Conclusion: In conclusion, this study introduces an innovative assessment tool aimed at evaluating common digital tool competencies. Our preliminary results demonstrate good acceptance and reveal expected group differences. For current cohorts of older adults, the results seem to indicate that the ability to use novel tools may aid digital tool use. In the next step, the psychometric properties of the DIGI assessment should be evaluated in larger and more diverse samples. The advancement of digital tool competency assessments and rehabilitation strategies is essential when we aim at facilitating societal inclusion and participation for individuals in affected populations.

Action goals and the praxis network: an fMRI study.

The praxis representation network (PRN) of the left cerebral hemisphere is typically linked to the control of functional interactions with familiar tools. Surprisingly, little is known about the PRN engagement in planning and execution of tool-directed actions motivated by non-functional but purposeful action goals. Here we used functional neuroimaging to perform both univariate and multi-voxel pattern analyses (MVPA) in 20 right-handed participants who planned and later executed, with their dominant and non-dominant hands, disparate grasps of tools for different goals, including: (1) planning simple vs. demanding functional grasps of conveniently vs. inconveniently oriented tools with an intention to immediately use them, (2) planning simple-but non-functional-grasps of inconveniently oriented tools with a goal to pass them to a different person, (3) planning reaching movements directed at such tools with an intention to move/push them with the back of the hand, and (4) pantomimed execution of the earlier planned tasks. While PRN contributed to the studied interactions with tools, the engagement of its critical nodes, and/or complementary right hemisphere processing, was differently modulated by task type. E.g., planning non-functional/structural grasp-to-pass movements of inconveniently oriented tools, regardless of the hand, invoked the left parietal and prefrontal nodes significantly more than simple, non-demanding functional grasps. MVPA corroborated decoding capabilities of critical PRN areas and some of their right hemisphere counterparts. Our findings shed new lights on how performance of disparate action goals influences the extraction of object affordances, and how or to what extent it modulates the neural activity within the parieto-frontal brain networks.

Manual praxis and language-production networks, and their links to handedness.

While Liepmann was one of the first researchers to consider a relationship between skilled manual actions (praxis) and language for tasks performed "freely from memory", his primary focus was on the relations between the organization of praxis and left-hemisphere dominance. Subsequent attempts to apply his apraxia model to all cases he studied - including his first patient, a "non-pure right-hander" treated as an exception - left the praxis-handedness issue unresolved. Modern neuropsychological and recent neuroimaging evidence either showed closer associations of praxis and language, than between handedness and any of these two functions, or focused on their dissociations. Yet, present-day developments in neuroimaging and statistics allow us to overcome the limitations of the earlier work on praxis-language-handedness links, and to better quantify their interrelationships. Using functional magnetic resonance imaging (fMRI), we studied tool use pantomimes and subvocal word generation in 125 participants, including righthanders (NRH = 52), ambidextrous individuals (mixedhanders; NMH = 31), and lefthanders (NLH = 42). Laterality indices were calculated both in two critical cytoarchitectonic maps, and 180 multi-modal parcellations of the human cerebral cortex, using voxel count and signal intensity, and the most relevant regions of interest and their networks were further analyzed. We found that atypical organization of praxis was present in all handedness groups (RH = 25.0%, MH = 22.6%; LH = 45.2%), and was about two and a half times as common as atypical organization of language (RH = 3.8%; MH = 6.5%; LH = 26.2%), contingent on ROI selection/LI-calculation method. Despite strong associations of praxis and language, regardless of handedness and typicality, dissociations of atypically represented praxis from typical left-lateralized language were common (~20% of cases), whereas the inverse dissociations of atypically represented language from typical left-lateralized praxis were very rare (in ~2.5% of all cases). The consequences of the existence of such different phenotypes for theoretical accounts of manual praxis, and its links to language and handedness are modeled and discussed.

The behavioural challenge of the COVID-19 pandemic: indirect measurements and personalized attitude changing treatments (IMPACT).

Following the outbreak of COVID-19 pandemic, governments around the globe coerced their citizens to adhere to preventive health behaviours, aiming to reduce the effective reproduction numbers of the virus. Driven by game theoretic considerations and inspired by the work of US National Research Council's Committee on Food Habits (1943) during WWII, and the post-WWII Yale Communication Research Program, the present research shows how to achieve enhanced adherence to health regulations without coercion. To this aim, we combine three elements: (i) indirect measurements, (ii) personalized interventions, and (iii) attitude changing treatments (IMPACT). We find that a cluster of short interventions, such as elaboration on possible consequences, induction of cognitive dissonance, addressing next of kin and similar others and receiving advice following severity judgements, improves individuals' health-preserving attitudes. We propose extending the use of IMPACT under closure periods and during the resumption of social and economic activities under COVID-19 pandemic, since efficient and lasting adherence should rely on personal attitudes rather than on coercion alone. Finally, we point to the opportunity of international cooperation generated by the pandemic.

Mental Shopping Calculations: A Transcranial Magnetic Stimulation Study.

One of the most critical skills behind consumer's behavior is the ability to assess whether a price after a discount is a real bargain. Yet, the neural underpinnings and cognitive mechanisms associated with such a skill are largely unknown. While there is general agreement that the posterior parietal cortex (PPC) on the left is critical for mental calculations, and there is also recent repetitive transcranial magnetic stimulation (rTMS) evidence pointing to the supramarginal gyrus (SMG) of the right PPC as crucial for consumer-like arithmetic (e.g., multi-digit mental addition or subtraction), it is still unknown whether SMG is involved in calculations of sale prices. Here, we show that the neural mechanisms underlying discount arithmetic characteristic for shopping are different from complex addition or subtraction, with discount calculations engaging left SMG more. We obtained these outcomes by remodeling our laboratory to resemble a shop and asking participants to calculate prices after discounts (e.g., $8.80-25 or $4.80-75%), while stimulating left and right SMG with neuronavigated rTMS. Our results indicate that such complex shopping calculations as establishing the price after a discount involve SMG asymmetrically, whereas simpler calculations such as price addition do not. These findings have some consequences for neural models of mathematical cognition and shed some preliminary light on potential consumer's behavior in natural settings.

Manual Grasparatus: A nifty tool for presenting real objects in fMRI research.

One of the greatest challenges in functional magnetic resonance imaging (fMRI) research using real objects as stimuli is their timely delivery and (pseudo)randomized presentation. To this end, we designed an apparatus which solves the majority of problems that fMRI researchers may encounter during testing. The display apparatus - here: delivering objects for manual exploration and grasping (hence the "Grasparatus") - is equipped with semi-attachable stimulus belts and, therefore, allows for presentation of numerous 3D objects in a pre-ordered sequence. Although the presentation is controlled manually and synchronized with fMRI scanning events via commands delivered to the experimenter, it is very reliable in conveying targets to their destination in different configurations and numbers. The stimuli are easily accessible to study participants either for manual or simple visual interactions because the device is highly adjustable. The main advantages of using this apparatus involve: •The easiness of its setup prior to a study and simplicity of its control during experimental functional MRI runs.•The possibility to use real size, magnet-friendly objects, firmly or semi-attached, so that different interactions are possible.•Fast exchange of stimulus sets between runs.

The neural underpinnings of haptically guided functional grasping of tools: An fMRI study.

The neural bases of haptically guided interactions with tools are largely unknown. Whereas in the visual domain there is clear evidence for left lateralization of the networks underlying the guidance of actions involving tools, comparable evidence in haptic modality is missing. Therefore, we examined whether the temporo-parieto-frontal networks responsive to interactions with tools also support haptically guided functional grasping. We used event-related functional magnetic resonance imaging (fMRI) to measure brain activity while, in the absence of vision, 21 right-handed participants performed the following tasks with either their dominant or non-dominant hands: haptic exploration of real 3-D tools or size-matched control objects, subsequent planning of functionally appropriate grasps of tools and most convenient grasps of non-tools, and the resulting grasp execution. As predicted, haptic exploration of tools (vs. non-tools) was associated with significant asymmetrical/left-lateralized increases of activity in temporo-parieto-frontal networks. While grasp planning did not reveal differences between tools and control objects, the execution of functional grasping of tools (as compared to control grasps) re-recruited mainly dorsal cortical regions engaged earlier during the exploration phase. These results demonstrate that haptically guided grasping of tools invokes only subsets of cortical regions typically associated with tool-directed actions. They also call for a re-interpretation of what we assumed would be happening during the exploration phase, as this early stage of processing most likely included preliminary grasp planning. After all, the requisite integration of structural and conceptual tool features, as well as relevant action knowledge mediated at the neuronal level by the temporo-parietal projections in the early stage of processing, is not then critical for the execution of the preprogrammed functional grasp.

The temporal involvement of the left supramarginal gyrus in planning functional grasps: A neuronavigated TMS study.

The left supramarginal gyrus (SMG) is a critical structure in tool use actions, including such simple acts as selection of appropriate grasps and, if necessary, their on-line corrections. Yet, its temporal contribution to initial planning of functional grasps of tools is largely unknown. We used MRI-guided, event-related transcranial magnetic stimulation (TMS) to determine the time point when SMG involvement in processing of tools for functional grasp decision was affected most. In Exp. 1, with 15 participants, triple-pulse (10 Hz) TMS was applied to either the left anterior-to-mid SMG (amSMG; subdivisions PFt/PF) or vertex at three different time points: starting from 17 ms (i.e., delivered at 17/117/217 ms), 117 ms (117/217/317 ms) or 217 ms (217/317/417 ms) after stimulus onset. In Exp. 2, with 12 participants, we applied single-pulse TMS to either left amSMG or the left rostral middle frontal gurus (rMFG; area 46) at these same time points relative to stimulus onset. Subject- and item-based analyses of response times (RTs) were performed. Whereas the amSMG and vertex stimulation with triple pulse has revealed differential effects on RTs in general, as well as on tool orientation processing, it gave only vague pointers as to their temporal contributions to the task. Yet, amSMG and rMFG stimulation with single pulse demonstrated that, while the processing in both of these areas can be enhanced at 17 ms and no doubt at 117 ms (as compared to 217 ms), the earliest stimulation facilitated amSMG (vs. rMFG) contribution, and the latest stimulation had the opposite effect, facilitating rMFG (vs. amSMG) contribution to planning functional grasps. These outcomes demonstrate that the critical role of SMG in tool-related actions can be invoked substantially earlier than previously thought.

Decoding Brain States for Planning Functional Grasps of Tools: A Functional Magnetic Resonance Imaging Multivoxel Pattern Analysis Study.

OBJECTIVES: We used multivoxel pattern analysis (MVPA) to investigate neural selectivity for grasp planning within the left-lateralized temporo-parieto-frontal network of areas (praxis representation network, PRN) typically associated with tool-related actions, as studied with traditional neuroimaging contrasts. METHODS: We used data from 20 participants whose task was to plan functional grasps of tools, with either right or left hands. Region of interest and whole-brain searchlight analyses were performed to show task-related neural patterns. RESULTS: MVPA revealed significant contributions to functional grasp planning from the anterior intraparietal sulcus (aIPS) and its immediate vicinities, supplemented by inputs from posterior subdivisions of IPS, and the ventral lateral occipital complex (vLOC). Moreover, greater local selectivity was demonstrated in areas near the superior parieto-occipital cortex and dorsal premotor cortex, putatively forming the dorso-dorsal stream. CONCLUSIONS: A contribution from aIPS, consistent with its role in prospective grasp formation and/or encoding of relevant tool properties (e.g., potential graspable parts), is likely to accompany the retrieval of manipulation and/or mechanical knowledge subserved by the supramarginal gyrus for achieving action goals. An involvement of vLOC indicates that MVPA is particularly sensitive to coding of object properties, their identities and even functions, for a support of grip formation. Finally, the engagement of the superior parieto-frontal regions as revealed by MVPA is consistent with their selectivity for transient features of tools (i.e., variable affordances) for anticipatory hand postures. These outcomes support the notion that, compared to traditional approaches, MVPA can reveal more fine-grained patterns of neural activity. (JINS, 2018, 24, 1013-1025).

Unique Neural Characteristics of Atypical Lateralization of Language in Healthy Individuals.

Using functional magnetic resonance imaging (fMRI) in 63 healthy participants, including left-handed and ambidextrous individuals, we tested how atypical lateralization of language-i. e., bilateral or right hemispheric language representation-differs from the typical left-hemisphere dominance. Although regardless of their handedness, all 11 participants from the atypical group engaged classical language centers, i.e., Broca's and Wernicke's areas, the right-hemisphere components of the default mode network (DMN), including the angular gyrus and middle temporal gyrus, were also critically involved during the verbal fluency task. Importantly, activity in these regions could not be explained in terms of mirroring the typical language pattern because left-hemisphere dominant individuals did not exhibit similar significant signal modulations. Moreover, when spatial extent of language-related activity across whole brain was considered, the bilateral language organization entailed more diffuse functional processing. Finally, we detected significant differences between the typical and atypical group in the resting-state connectivity at the global and local level. These findings suggest that the atypical lateralization of language has unique features, and is not a simple mirror image of the typical left hemispheric language representation.

Numbers and functional lateralization: A visual half-field and dichotic listening study in proficient bilinguals.

Potential links between language and numbers and the laterality of symbolic number representations in the brain are still debated. Furthermore, reports on bilingual individuals indicate that the language-number interrelationships might be quite complex. Therefore, we carried out a visual half-field (VHF) and dichotic listening (DL) study with action words and different forms of symbolic numbers used as stimuli to test the laterality of word and number processing in single-, dual-language and mixed -task and language- contexts. Experiment 1 (VHF) showed a significant right visual field/left hemispheric advantage in response accuracy for action word, as compared to any form of symbolic number processing. Experiment 2 (DL) revealed a substantially reversed effect - a significant right ear/left hemisphere advantage for arithmetic operations as compared to action word processing, and in response times in single- and dual-language contexts for number vs. action words. All these effects were language independent. Notably, for within-task response accuracy compared across modalities significant differences were found in all studied contexts. Thus, our results go counter to findings showing that action-relevant concepts and words, as well as number words are represented/processed primarily in the left hemisphere. Instead, we found that in the auditory context, following substantial engagement of working memory (here: by arithmetic operations), there is a subsequent functional reorganization of processing single stimuli, whether verbs or numbers. This reorganization - their weakened laterality - at least for response accuracy is not exclusive to processing of numbers, but the number of items to be processed. For response times, except for unpredictable tasks in mixed contexts, the "number problem" is more apparent. These outcomes are highly relevant to difficulties that simultaneous translators encounter when dealing with lengthy auditory material in which single items such as number words (and possibly other types of key words) need to be emphasized. Our results may also shed a new light on the "mathematical savant problem".

Planning Functional Grasps of Simple Tools Invokes the Hand-independent Praxis Representation Network: An fMRI Study.

OBJECTIVES: Neuropsychological and neuroimaging evidence indicates that tool use knowledge and abilities are represented in the praxis representation network (PRN) of the left cerebral hemisphere. We investigated whether PRN would also underlie the planning of function-appropriate grasps of tools, even though such an assumption is inconsistent with some neuropsychological evidence for independent representations of tool grasping and skilled tool use. METHODS: Twenty right-handed participants were tested in an event-related functional magnetic resonance imaging (fMRI) study wherein they planned functionally appropriate grasps of tools versus grasps of non-tools matched for size and/or complexity, and later executed the pantomimed grasps of these objects. The dominant right, and non-dominant left hands were used in two different sessions counterbalanced across participants. The tool and non-tool stimuli were presented at three different orientations, some requiring uncomfortable hand rotations for effective grips, with the difficulty matched for both hands. RESULTS: Planning functional grasps of tools (vs. non-tools) was associated with significant asymmetrical increases of activity in the temporo/occipital-parieto-frontal networks. The greater involvement of the left hemisphere PRN was particularly evident when hand movement kinematics (including wrist rotations) for grasping tools and non-tools were matched. The networks engaged in the task for the dominant and non-dominant hand were virtually identical. The differences in neural activity for the two object categories disappeared during grasp execution. CONCLUSIONS: The greater hand-independent engagement of the left-hemisphere praxis representation network for planning functional grasps reveals a genuine effect of an early affordance/function-based visual processing of tools. (JINS, 2017, 23, 108-120).

Left extrastriate body area is sensitive to the meaning of symbolic gesture: evidence from fMRI repetition suppression.

Functional magnetic resonance imaging (fMRI) adaptation (a.k.a. repetition suppression) paradigm was used to test if semantic information contained in object-related (transitive) pantomimes and communicative (intransitive) gestures is represented differently in the occipito-temporal cortex. Participants watched 2.75 s back-to-back videos where the meaning of gesture was either repeated or changed. The just observed (typically second) gesture was then imitated. To maintain participants' attention, some trials contained a single video. fMRI adaptation -signal decreases- for watching both movement categories were observed particularly in the lateral occipital cortex, including the extrastriate body area (EBA). Yet, intransitive (vs. transitive) gesture specific repetition suppression was found mainly in the left rostral EBA and caudal middle temporal gyrus- the rEBA/cMTG complex. Repetition enhancement (signal increase) was revealed in the precuneus. While the whole brain and region-of-interest analyses indicate that the precuneus is involved only in visuospatial action processing for later imitation, the common EBA repetition suppression discloses sensitivity to the meaning of symbolic gesture, namely the "semantic what" of actions. Moreover, the rEBA/cMTG suppression reveals greater selectivity for conventionalized communicative gesture. Thus, fMRI adaptation shows higher-order functions of EBA, its role in the semantic network, and indicates that its functional repertoire is wider than previously thought.

Specialization of the left supramarginal gyrus for hand-independent praxis representation is not related to hand dominance.

Data from focal brain injury and functional neuroimaging studies implicate a distributed network of parieto-fronto-temporal areas in the human left cerebral hemisphere as playing distinct roles in the representation of meaningful actions (praxis). Because these data come primarily from right-handed individuals, the relationship between left cerebral specialization for praxis representation and hand dominance remains unclear. We used functional magnetic resonance imaging (fMRI) to evaluate the hypothesis that strongly left-handed (right hemisphere motor dominant) adults also exhibit this left cerebral specialization. Participants planned familiar actions for subsequent performance with the left or right hand in response to transitive (e.g., "pounding") or intransitive (e.g. "waving") action words. In linguistic control trials, cues denoted non-physical actions (e.g., "believing"). Action planning was associated with significant, exclusively left-lateralized and extensive increases of activity in the supramarginal gyrus (SMg), and more focal modulations in the left caudal middle temporal gyrus (cMTg). This activity was hand- and gesture-independent, i.e., unaffected by the hand involved in subsequent action performance, and the type of gesture (i.e., transitive or intransitive). Compared directly with right-handers, left-handers exhibited greater involvement of the right angular gyrus (ANg) and dorsal premotor cortex (dPMC), which is indicative of a less asymmetric functional architecture for praxis representation. We therefore conclude that the organization of mechanisms involved in planning familiar actions is influenced by one's motor dominance. However, independent of hand dominance, the left SMg and cMTg are specialized for ideomotor transformations-the integration of conceptual knowledge and motor representations into meaningful actions. These findings support the view that higher-order praxis representation and lower-level motor dominance rely on dissociable mechanisms.

Reliability and validity of neurobehavioral function on the Psychology Experimental Building Language test battery in young adults.

Background. The Psychology Experiment Building Language (PEBL) software consists of over one-hundred computerized tests based on classic and novel cognitive neuropsychology and behavioral neurology measures. Although the PEBL tests are becoming more widely utilized, there is currently very limited information about the psychometric properties of these measures. Methods. Study I examined inter-relationships among nine PEBL tests including indices of motor-function (Pursuit Rotor and Dexterity), attention (Test of Attentional Vigilance and Time-Wall), working memory (Digit Span Forward), and executive-function (PEBL Trail Making Test, Berg/Wisconsin Card Sorting Test, Iowa Gambling Test, and Mental Rotation) in a normative sample (N = 189, ages 18-22). Study II evaluated test-retest reliability with a two-week interest interval between administrations in a separate sample (N = 79, ages 18-22). Results. Moderate intra-test, but low inter-test, correlations were observed and ceiling/floor effects were uncommon. Sex differences were identified on the Pursuit Rotor (Cohen's d = 0.89) and Mental Rotation (d = 0.31) tests. The correlation between the test and retest was high for tests of motor learning (Pursuit Rotor time on target r = .86) and attention (Test of Attentional Vigilance response time r = .79), intermediate for memory (digit span r = .63) but lower for the executive function indices (Wisconsin/Berg Card Sorting Test perseverative errors = .45, Tower of London moves = .15). Significant practice effects were identified on several indices of executive function. Conclusions. These results are broadly supportive of the reliability and validity of individual PEBL tests in this sample. These findings indicate that the freely downloadable, open-source PEBL battery (http://pebl.sourceforge.net) is a versatile research tool to study individual differences in neurocognitive performance.

Co-lateralized bilingual mechanisms for reading in single and dual language contexts: evidence from visual half-field processing of action words in proficient bilinguals.

When reading, proficient bilinguals seem to engage the same cognitive circuits regardless of the language in use. Yet, whether or not such "bilingual" mechanisms would be lateralized in the same way in distinct-single or dual-language contexts is a question for debate. To fill this gap, we tested 18 highly proficient Polish (L1) -English (L2) childhood bilinguals whose task was to read aloud one of the two laterally presented action verbs, one stimulus per visual half field. While in the single-language blocks only L1 or L2 words were shown, in the subsequent mixed-language blocks words from both languages were concurrently displayed. All stimuli were presented for 217 ms followed by masks in which letters were replaced with hash marks. Since in non-simultaneous bilinguals the control of language, skilled actions (including reading), and representations of action concepts are typically left lateralized, the vast majority of our participants showed the expected, significant right visual field advantage for L1 and L2, both for accuracy and response times. The observed effects were nevertheless associated with substantial variability in the strength of the lateralization of the mechanisms involved. Moreover, although it could be predicted that participants' performance should be better in a single-language context, accuracy was significantly higher and response times were significantly shorter in a dual-language context, irrespective of the language tested. Finally, for both accuracy and response times, there were significant positive correlations between the laterality indices (LIs) of both languages independent of the context, with a significantly greater left-sided advantage for L1 vs. L2 in the mixed-language blocks, based on LIs calculated for response times. Thus, despite similar representations of the two languages in the bilingual brain, these results also point to the functional separation of L1 and L2 in the dual-language context.

Structural asymmetry of the insula is linked to the lateralization of gesture and language.

The control of gesture is one of the most left-lateralized functions, and the insular cortex is one of the most left-biased structures in the human brain. Therefore, we investigated whether structural asymmetries of the insula are linked to the organization of functional activity during gesture planning. We reconstructed and parcellated the insular cortex of 27 participants. First, we tested 15 strongly left-handed individuals because of a higher incidence of atypical organization of functions such as gesture and language in such a population. The inter-hemispheric structural asymmetries were compared with the lateralization of activity for gesture in the supramarginal gyrus (the hotspot of signal increase regardless of the gesturing hand) and Broca's area (the hotspot of signal increase for language production). The more pronounced leftward structural asymmetries were accompanied by greater left-hemisphere dominance for both of the studied functions. Conversely, an atypical, bilateral or rightward functional shift of gesture and language was accompanied by an attenuated leftward asymmetry of the insula. These significant relationships were driven primarily by differences in surface area. Subsequently, by adding 12 right-handed individuals to these analyses we demonstrated that the observed significant associations are generalizable to the population. These results provide the first demonstration of the relationships between structural inter-hemispheric differences of the insula and the cerebral specialization for gesture. They also corroborate the link between insular asymmetries and language lateralization. As such, these outcomes are relevant to the common cerebral specialization for gesture and language.

Sinistrals are rarely "right": evidence from tool-affordance processing in visual half-field paradigms.

Although current neuroscience and behavioral studies provide substantial understanding of tool representations (e.g., the processing of tool-related affordances) in the human brain, most of this knowledge is limited to right-handed individuals with typical organization of cognitive and manual skills. Therefore, any insights from these lines of research may be of little value in rehabilitation of patients with atypical laterality of praxis and/or hand dominance. To fill this gap, we tested perceptual processing of man-made objects in 18 healthy left-handers who were likely to show greater incidence of right-sided or bilateral (atypical) lateralization of functions. In the two experiments reported here, participants performed a tool vs. non-tool categorization task. In Experiment 1, target and distracter objects were presented for 200 ms in the left (LVF) or right (RVF) visual field, followed by 200 ms masks. In Experiment 2, the centrally presented targets were preceded by masked primes of 35 ms duration, again presented in the LVF or RVF. Based on results from both studies, i.e., response times (RTs) to correctly discriminated stimuli irrespective of their category, participants were divided into two groups showing privileged processing in either left (N = 9) or right (N = 9) visual field. In Experiment 1, only individuals with RVF advantage showed significantly faster categorization of tools in their dominant visual field, whereas those with LVF advantage revealed merely a trend toward such an effect. In Experiment 2, when targets were preceded by identical primes, the "atypical" group showed significantly facilitated categorization of non-tools, whereas the "typical" group demonstrated a trend toward faster categorization of tools. These results indicate that in subjects with atypically organized cognitive skills, tool-related processes are not just mirror reversed. Thus, our outcomes call for particular caution in neurorehabilitation directed at left-handed individuals.