Functional asymmetries, most commonly associated in humans with population-level hand preference and lateralization in language processing, are complex, heterogeneous traits with poorly understood biological and genetic bases. Notably, functional asymmetries are also associated with familial non-right handedness suggesting that common genetic factors influence both handedness and functional lateralization. This dissertation has two aims. The first is the development of a specific biological hypothesis that may partially account for the consistent co-lateralization of hand preference and prefrontal language function. I argue that asymmetries in local neural properties that affect the excitability and signal-to-noise ratio of neural assemblies can produce a bias in the direction and, to some extent, the degree of functional lateralization for complex functions. At a high level of representation, this hypothesis is similar to long-standing theories of hemispheric differences, but differs from these by providing a single biological difference between hemispheres that influences both motor and prefrontal asymmetries. Specifically, I propose that a hemispheric asymmetry in the ratio of activity at D1 and D2 dopamine receptors can account for both forms of asymmetry. The second aim is to identify novel electrophysiological and behavioral correlates of genetic effects linked to handedness. By applying a standard genetic model to familial handedness data, I obtain an estimate of these genetic effects for individual research participants that may improve sensitivity over previous studies that have primarily used categorical classifications to study familial handedness effects. Two EEG studies of executive function provide evidence for computational changes associated with familial handedness. The first, an auditory oddball paradigm, suggests that cortical noise is increased in conjunction with estimated genetic effects associated with left handedness. In the second study, a go-nogo task, a dissociation between response inhibition and response conflict processing was found with respect to estimated genetic effects associated with left handedness. In addition to bearing on current theories of conflict processing, these results may provide indirect evidence for dopaminergic contributions to neurological and behavioral differences associated with familial sinistrality. Additional studies of resting EEG and behavioral responses to Necker cube viewing provide additional evidence for broad effects of familial sinistrality.

Lateralized behaviour is the most conspicuous manifestation of hemispheric specialization of the brain and has been reported in a variety of taxa. Only a few studies have so far assessed lateralized behaviours in horses. Therefore, I observed ten domestic horses for 16 weeks for an array of spontaneously occurring motor behaviours as well as stimulus-induced behavioural responses to determine if they display side preferences at the individual or population level and to assess possible correlations between lateralized behaviours. Significant side preferences were found for certain behaviours at the individual level, ranging from standing and flexing, to auditory stimuli, and olfactory stimuli. All horses showed task-dependent changes in their side preferences and no significant side preferences were found at the population level for any behaviours. Similarly, no significant correlations were found between behaviours. Taken together, the results of the present study suggest that horses, like all other species studied so far except humans and some great apes, only display lateralized behaviour at the individual, but not at the population level.

Research in neuropsychology has found depression to be related to impaired right hemisphere (RH) functioning. How clinical depression affects brain lateralized functioning for each sex, however, is not clear. The main aim of this thesis was to investigate how clinical depression impacts brain lateralized functioning for each sex. Additionally, this thesis investigates brain lateralization for emotional processing in a non-depressed group, as well as sex differences in brain lateralization for spatial, verbal, and emotional processing in a non-depressed group. In order to examine each of these research areas, sixty non-depressed participants, and thirty-nine dilnically depressed patients were recnjited to complete a set of neuropsychological tasks that measure brain lateralized spatial, verbal, and emotional functioning. The neuropsychological tasks that were selected also measure the brain regions known to be involved with depression (frontal lobe and right parietal lobe). The tasks were: the mental rotation task (MRT) to measure RH spatial functioning; the verbal fluency task (phonemic and semantic) to measure left hemisphere (LH) verbal functioning; and the chimeric faces task to measure frontal lobe emotional functioning. The data from these tasks were reported as two separate experiments. Experiment One examined sex differences in brain lateralization for spatial and verbal processing in a non-depressed group. Experiment One also investigates brain lateralization for emotional processing in a non-depressed group, in particular to determine whether there is a sex difference in brain lateralization for emotional processing. The aim of Experiment One was to replicate the male advantage in spatial processing and the female advantage in verbal processing, which have previously been interpreted as reflecting sex differences in brain lateralization for these functions. It was also the aim to differentiate between the competing RH and valence hypotheses of brain lateralization for emotional processing and further investigate sex differences in brain lateralization for emotional processing. Sex differences in brain lateralization for spatial, verbal, and emotional processing were examined by comparing the performance of thirty non-depressed males and thirty non-depressed females on the MRT, verbal fluency task, and chimeric faces task respectively. The hypothesis that males would mentally rotate the stimuli of the MRT faster than the females was not supported, as no significant sex differences in performance were observed on the MRT. Failure to replicate the male advantage in spatial functioning was attributed to a possible sex difference in level of spatial ability, which has been found to mediate hemispheric functioning. The hypothesis that the females would generate significantly more words than the males on the verbal fluency task was supported, thus replicating the female advantage in verbal processing. For the chimeric faces task, the group findings supported the RH hypothesis for brain lateralization for emotional processing, with responses being significanfly faster and more accurate to happy and sad expressions shown in the LVF than in the RVF. No consistent sex differences in performance were observed between the RT and accuracy rate analyses of the chimeric faces task. Reaction times to the chimeric faces showed a LVF advantage in emotional processing for the males, and no hemispheric bias for emotional processing for the females. In contrast, recognition accuracy of the chimeric faces showed a LVF advantage for emotional processing for both the males and the females. The inconsistent sex differences on the chimeric faces task suggests that there is not a strong sex difference in brain lateralization for emotional processing. Expertment Two investigated brain lateralization for spatial, verbal, and emotional functioning in a clinically depressed group. It was the aim of Experiment Two to determine whether clinical depression is associated with impaired RH functioning, as suggested by the literature. It was also the aim of Experiment Two to examine more specifically, how clinical depression affects brain lateralized functioning for each sex separately. To examine the effect of clinical depression on brain lateralized functioning, the performance of thirty-six (fifteen males, twenty-one females) clinically depressed patients (three excluded from the recruited thirty-nine) and thirty-six (eighteen males, eighteen females) non-depressed control participants was compared on the MRT, verbal fluency task, and chimeric faces task. The hypothesis that clinical depression would be associated with impaired RH functioning was partially supported by the results of Experiment Two. The depressed group performed signiflcantiy poorer than the control group on both the RH task (the MRT intercept and overall R and the LH task (semantic verbal fluency). Therefore, impaired RH and LH functioning on the spatial and verbal task was evidenced for the clinically depressed group in Experiment Two. A RH impairment in emotional functioning with clinical depression could not be clearly ascertained from the results of the chimeric faces task. The RT analyses of the chimeric faces task showed a LVF advantage for emotional processing for both the control and depressed groups. In contrast to the RT analyses, the accuracy rate analyses of the chimeric faces task showed a LVF advantage in emotional processing for the control group, and no hemispheric bias for emotional processing for the depressed group, As the depressed group were significantly impaired for both RH and LH functioning in Experiment Two, it is possible that the findings of Experiment Two are reflective of a generalised performance deficit associated with clinical depression, rather than to a disturbance in brain lateralized functioning. The depressed group was also found to respond significantly slower than the control group in overall RT on the MRT and chimeric faces task. The significant group difference on the intercept of the FART implicates impaired information encoding for the clinically depressed group. The slowed Ris of the depressed group may also reflect impaired pre-motor organization with clinical depression, thus resulting in delayed motor responses. In relation to the affect of clinical depression on brain lateralizaflon for each sex, it was hypothesised that the depressed males would perform significantly poorer than the depressed females on tasks measuring functions lateralized to the cerebral hemisphere impaired due to clinical depression. The premise for this hypothesis lies in the evidence from past unilateral brain lesion research, which suggests that the stronger brain ateralization of males restricts assistance from the unimpaired hemisphere to perform the task of the impalred hemisphere. The bilateralization of females however, allows greater assistance of the unimpaired hemisphere to perform the task at hand. In contrast to the hypothesis however, there was no evidence from the results of Experiment Two that clinical depression had a greater impact on the brain lateralized functioning of males than females. No significant sex differences in performance on the FART were observed for either the non-depressed control group or clinical depressed group. For the verbal fluency task, a female advantage in word generation was observed for both phonemic and semantic fluency, regardless of group. Also regardless of group, the RT analyses of the chimeric faces task showed that the males responded significantly faster to emotional expressions shown in the LVF than in the RVF. For the females however, there was no hemispheric bias in RT for emotional processing. The accuracy rate analyses from the chimeric faces task also showed no sex differences for either group. The similar findings of sex differences between the control and depressed groups across each task suggests that clinical depression had a similar impact on both the males and the females, regardless of brain late ralization. The results of Experiment Two could be indicative of impaired LH and RH functioning with clinical depression, or of a generalised performance deficit with clinical depression. A generalised performance deficit for the clinically depressed group in Experiment Two may explain why a sex difference in the effects of clinical depression on brain lateralized functioning was not observed. Future research observing a RH impairment with clinical depression is encouraged to further examine the affect of clinical depression on brain lateralization for each sex separately. Further understanding of the affect of clinical depression on brain lateralization for each sex could provide addiional information on sex difference in the prevalence of clinical depression.

For children with intractable epilepsy, surgery provides significant reduction in seizure frequency, with no significant declines in intellectual or behavioral functioning (Datta, et al., 2011). Prior to surgery, children must undergo a thorough assessment to determine the location of the seizure-focus and to evaluate risks of post-operative impairment (Lee, 2010). Currently, fMRI offers one of the most reliable and least invasive means of localizing language prior to surgery (McDonald, Saykin, William & Assaf, 2006). Dichotic listening, a behavioral task in which subjects are asked to listen to two competing stimuli simultaneously, offers a possible alternative for children who cannot complete fMRI studies. Previous studies have relied on research-based listening tasks and the type of quantitative analysis of the fMRI rarely available in the clinical setting. Instead, this study examined how well dichotic listening results predict language lateralization from fMRI within a clinical setting. Data were gathered through a records review of 13 children with intractable epilepsy referred to Austin Neuropsychology through the epilepsy treatment team at Dell Children’s Medical Center. Overall, children classified as atypical language dominance on the fMRI studies showed lower levels of right ear advantage on the dichotic listening measure. Despite this trend, a discriminant analysis using the dichotic listening results to predict fMRI classification showed no significant improvement over chance classification. A secondary analysis examined factors related to a child’s ability to complete an fMRI language study, comparing 12 children from the original sample with 6 children referred through the same process and over the same time period who could not obtain a successful fMRI determination of language lateralization. Overall, children who successfully completed the fMRI language studies showed a trend of lower levels of difficulty with behavioral regulation and higher levels of intelligence. Although the non-significant results highlight the limitations of dichotic listening as a clinical tool, the failure rate within the total sample, along with the information about the roles of intelligence and behavioral regulation, may help spur the development of alternative methods of language lateralization. / text

Age-related decline in memory and other cognitive functions, such as visuospatial functions is widely studied and well documented. In recent years, some studies have also found relationships between memory performance and functional body lateralization, with individuals who are inconsistently lateralized (e.g. have inconsistent handedness) scoring higher on episodic memory tests. The objectives of this study were to investigate relationships and possible differences between episodic and semantic memory performance, and visuospatial functions as a function of functional lateralization consistency in a large population-based study. In total, 1283 adult men and women participants, with age ranging from 25 to 100 years, were tested within the Betula prospective cohort study (Nilsson et al., 1997) where they were included in the fifth wave (T5) of data collection. Participants were divided into groups of consistent or inconsistent functional lateralization regarding respective hand-, foot-, and eyedness. Results revealed weak to moderate relationship between variables of functional laterality and its consistency. While age was significant predictor of memory performance and visuospatial functions, sex and functional laterality consistency variables were insignificant. Results are discussed in relation to previous studies and to hemispheric interaction theory. / Betula prospective cohort study (Nilsson et al., 1997, 2004)

No description available.

Participants with Down syndrome (DS) as well as typically developing peers matched for mental and chronological age completed a 3-step movement sequence in response to visual (lights), verbal (spoken word), meaningful auditory (music), and non-meaningful auditory (tones) instructions. Results indicate that participants with DS demonstrated slower reaction time in the visual condition but were more consistent in their movement time and made fewer errors suggesting they adopted a strategy in which they traded speed for accuracy. Further, they were slowest, most variable, and made the most errors in the non-meaningful auditory condition indicating that the amount of meaning associated with the method of instruction is an important determinant of motor performance. These results support the assertion that motor performance for persons with DS is determined in part by the unique pattern of cerebral lateralization for this population while at the same time demonstrating the importance of task and stimulus familiarity.

This experiment tested hypotheses linking the right cerebral regulation of hostility and cardiovascular reactivity. First, replication of previous research supporting heightened cardiovascular reactivity (mean arterial pressure, systolic blood pressure, diastolic blood pressure, and heart rate) among high-hostile participants was attempted. Second, dynamic variations in functional cerebral asymmetry in response to pain (cold pressor stressor) and affective verbal learning (positive and negative valenced word lists) were measured. High- and low-hostile participants (n = 64) were identified using the Cook Medley Hostility Scale. Participants completed either the cold-pressor stressor condition or the no-stress control condition as well as the negative and the positive affective verbal learning test. Cardiovascular measures (MAP, SBP, DBP, and HR) before and after the stress or no-stress condition and before and after the negative and the positive affective learning tasks were recorded. The results demonstrated that high-hostiles had difficulty processing emotional stimuli. High-hostiles were reliably impaired in emotional word learning. Further, results suggested that negative affective learning produced proactive interference for the learning or recall of subsequently presented information. Positive affective learning produced diametrically opposite effects with retroactive interference for the recall of previously presented information. Also, high-hostiles' cardiovascular reactivity to a physical stressor was independent of the valence of the learning task. In contrast, low-hostiles' cardiovascular reactivity was valence dependent with activation to both the positive list concurrent with stress and to the negative list concurrent with no stress. Finally, the results indicated that the effect of the affective learning lists, on the heart, is stress dependent. Neuropsychological theories of ANS regulation and emotion are discussed in relation to the primary findings and a new model of lateralized regulation is proposed. / Ph. D.

Visual perception theory distinguishes between two distinct levels of object processing: holistic, based on global shape, and configural, based on local features and/or component parts. Empirical evidence suggests that different cortical regions may support these levels; holistic processing correlates with activation in the lateral occipital-temporal cortex (LOC), whereas configural processes correspond to activation in the parietal lobe, particularly the intraparietal sulcus (IPS). This study combined theories of visual part structure with neuroimaging methods to investigate the relative contribution of holistic and configural processing in an ecologically valid object recognition task. Rather than rely on stimuli specifically designed to evoke holistic or configural processing, this study used photographs of objects selected without a priori assumptions concerning physical part structure. Twenty participants viewed objects at fixation while undergoing fMRI, followed by a behavioral object identification task involving the same objects presented in peripheral vision. Behavioral data were analyzed according to theories of visual crowding to yield an objective estimate of the number of parts perceived within each object. Neuroimaging results revealed increased activation for holistic objects containing fewer parts in the right parietal lobe and superior temporal gyrus and bilaterally in the fusiform gyrus, suggesting a relation between holistic processing areas and object perception. Configural objects with many parts elicited increased activation in the left angular gyrus. This study, to our knowledge, is the first to investigate the cortical visual regions involved when observers engage in holistic and configural processing as a natural part of visual recognition. / Master of Science

Det har tidigare rapporterats att icke-stammande personer har en tydlig vänstersidig cerebral lateralisering vad gäller talmotoriken, vilket visas genom ökad högersidig aktivering i läppmuskulaturen. Personer med stamning har å andra sidan föreslagits ha ett vänstersidigt eller bilateralt aktiveringsmönster av talmuskulaturen. Detta antas vara en av orsakerna till stamning. Testdeltagarna i aktuell studie bestod av 11 stammande och 13 matchade icke-stammande vuxna. Uppgifterna bestod av ordrepetition, ordgenerering samt att puta med läpparna. EMG-aktivitet från musklerna orbicularis oris och depressor labii inferior registrerades med elektroder på höger och vänster sida av läppmuskulaturen. Syftet med aktuell studie var att undersöka eventuell skillnad i läppasymmetri mellan stammande och icke-stammande vuxna personer. Resultatet kunde inte påvisa signifikanta gruppskillnader i grad av muskelaktivering för läppmuskulaturen. Båda grupperna uppvisade tvärtemot förväntan en nästintill bilateral aktivitet. En tendens till positiv korrelation, om än inte statistiskt signifikant, kunde observeras mellan grad av uppvisad stamning och något mer högersidig muskelaktivering.