Brain lateralization of complex movement: Neuropsychological evidence from unilateral stroke

Complex movement (CM) refers to the representation of a goal-oriented action and is classified as either transitive (use of tools) or intransitive (communication gestures). Both types of CM have three specific components: temporal, spatial, and content, which are subdivided into specific error types (SET). Since there is debate regarding the contribution of each brain hemisphere for the types of CM, our objective was to describe the brain lateralization of components and SET of transitive and intransitive CM. We studied 14 patients with a left hemisphere stroke (LH), 12 patients with a right hemisphere stroke (RH), and 16 control subjects. The Florida Apraxia Screening Test-Revised (FAST-R, Rothi et al., 1988) was used for the assessment of CM. Both clinical groups showed a worse performance than the control group on the total FAST-R and transitive movement scores (p < 0.001). Failures in Spatial and Temporal components were found in both clinical groups, but only LH patients showed significantly more Content errors (p < 0.01) than the control group. Also, only the LH group showed a higher number of errors for intransitive movements score (p = 0.017), due to lower scores in the content component, compared to the control group (p = 0.04). Transitive and intransitive CMs differ in their neurocognitive representation; transitive CM shows a bilateral distribution of its components when compared to intransitive CM, which shows a preferential left hemisphere representation. This could result from higher neurocognitive demands for movements that require use of tools, compared with more automatic communication gestures.     

Differential effect of ill-being and chronic stress on cradling behavior of first and multi-time parents

A preference for cradling infants on the left side has been demonstrated in women, as has a relation of reduced left-cradling and stress/negative affect. This relation has not yet been investigated in male participants. Due to less left-cradling in non-fathers compared to fathers it was suggested that fatherhood might have an influence on cradling behavior. The present study investigated the cradling preference of first- and multi-time parents before and after birth, and its relation to ill-being and stress. Results revealed that cradling behavior of first-time fathers was not different before and after the birth of the infant. Thus, fatherhood does not seem to have an acute influence on cradling behavior. Furthermore, cradling behavior of first- and multi-time parents was differentially influenced by ill-being and stress.These results present new information about the course of cradling preference from pregnancy to postpartum and indicate that the relation of cradling and ill-being/stress is more complex for parents than for non-parents.     

Lateral biases and reading direction: a dissociation between aesthetic preference and line bisection

Perceptual asymmetries for tasks involving aesthetic preference or line bisection can be affected by asymmetrical neurological mechanisms or left/right reading habits. This study investigated the relative contribution of these mechanisms in 100 readers of Japanese and English. Participants made aesthetic judgments between pairs of mirror-reversed pictures showing: (a) static objects, (b) moving objects and (c) landscapes. A line bisection task was also administered. There was a strong effect of reading direction for static and mobile objects whereby Japanese readers preferred objects with a right-to-left directionality (and vice versa for English readers). In contrast, similar patterns were observed for the Japanese and English readers for the landscape and line bisection tasks. The results show that reading habits affect aesthetic judgments for static and moving object tasks, but not the landscape and line bisection tasks. The difference between the tasks may be related to the horizontal/vertical geometry of the stimuli, which makes the landscape and line bisection tasks more prone to universal effects related to cerebral dominance.     

BOLD response to motion verbs in left posterior middle temporal gyrus during story comprehension

A primary focus within neuroimaging research on language comprehension is on the distribution of semantic knowledge in the brain. Studies have shown that the left posterior middle temporal gyrus (LPMT), a region just anterior to area MT/V5, is important for the processing of complex action knowledge. It has also been found that motion verbs cause activation in LPMT. In this experiment we investigated whether this effect could be replicated in a setting resembling real life language comprehension, i.e. without any overt behavioral task during passive listening to a story. During fMRI participants listened to a recording of the story “The Ugly Duckling”. We incorporated a nuisance elimination regression approach for factoring out known nuisance variables both in terms of physiological noise, sound intensity, linguistic variables and emotional content. Compared to the remaining text, clauses containing motion verbs were accompanied by a robust activation of LPMT with no other significant effects, consistent with the hypothesis that this brain region is important for processing motion knowledge, even during naturalistic language comprehension conditions.     

Evidence for right hemisphere phonology in a backward masking task

The extent to which orthographic and phonological processes are available during the initial moments of word recognition within each hemisphere is under specified, particularly for the right hemisphere. Few studies have investigated whether each hemisphere uses orthography and phonology under constraints that restrict the viewing time of words and reduce overt phonological demands. The current study used backward masking in the divided visual field paradigm to explore hemisphere differences in the availability of orthographic and phonological word recognition processes. A 20 ms and 60 ms SOA were used to track the time course of how these processes develop during pre-lexical moments of word recognition. Nonword masks varied in similarity to the target words such that there were four types: orthographically and phonologically similar, orthographically but not phonologically similar, phonologically but not orthographically similar and unrelated. The results showed the left hemisphere has access to both orthography and phonology early in the word recognition process. With more time to process the stimulus, the left hemisphere is able to use phonology which benefits word recognition to a larger extent than orthography. The right hemisphere also demonstrates access to both orthography and phonology in the initial moments of word recognition, however, orthographic similarity improves word recognition to a greater extent than phonological similarity.     

Prominence vs. aboutness in sequencing: A functional distinction within the left inferior frontal gyrus

Prior research on the neural bases of syntactic comprehension suggests that activation in the left inferior frontal gyrus (lIFG) correlates with the processing of word order variations. However, there are inconsistencies with respect to the specific subregion within the IFG that is implicated by these findings: the pars opercularis or the pars triangularis. Here, we examined the hypothesis that the dissociation between pars opercularis and pars triangularis activation may reflect functional differences between clause-medial and clause-initial word order permutations, respectively. To this end, we directly compared clause-medial and clause-initial object-before-subject orders in German in a within-participants, event-related fMRI design. Our results showed increased activation for object-initial sentences in a bilateral network of frontal, temporal and subcortical regions. Within the lIFG, posterior and inferior subregions showed only a main effect of word order, whereas more anterior and superior subregions showed effects of word order and sentence type, with higher activation for sentences with an argument in the clause-initial position. These findings are interpreted as evidence for a functional gradation of sequence processing within the left IFG: posterior subportions correlate with argument prominence-based (local) aspects of sequencing, while anterior subportions correlate with aboutness-based aspects of sequencing, which are crucial in linking the current sentence to the wider discourse. This proposal appears compatible with more general hypotheses about information processing gradients in prefrontal cortex (Koechlin & Summerfield, 2007).     

The Contribution of Attention to the Right Visual Field Advantage for Word Recognition

Perceptual asymmetries have been explained by structural, attentional bias and attentional advantage models. Structural models focus on asymmetries in the physical access information has to the hemispheres, whereas attentional models focus on asymmetries in the operation of attentional processes. A series of experiments was conducted to assess the contribution of attentional mechanisms to the right visual field (RVF) advantage found for word recognition. Valid, invalid and neutral peripheral cues were presented at a variety of stimulus onset asynchronies to manipulate spatial attention. Results indicated a significant RVF advantage and cueing effect. The effect of the cue was stronger for the left visual field than the RVF. This interaction supports the attentional advantage model which suggests that the left hemisphere requires less attention to process words. The attentional asymmetry is interpreted in terms of the different word processing styles used by the left and right hemispheres. These results have ramifications for the methodology used in divided visual field research and the interpretation of this research.