Aberrant auditory processing and atypical planum temporale in developmental stuttering.

OBJECTIVE: To learn if people with persistent developmental stuttering and atypical anatomy of their auditory temporal cortex have, when compared to control subjects, changes in fluency induced with delayed auditory feedback (DAF). BACKGROUND: DAF improves fluency in many individuals who stutter, and induces dysfluency in some normal people. The planum temporale (PT), a portion of auditory temporal cortex, is anatomically atypical in some adults who stutter and atypical anatomy might induce aberrant function. Thus, the people who demonstrate the paradoxical response to DAF might be those who have atypical anatomy. METHODS: Experimental subjects were adults with developmental stuttering (n = 14) and control subjects (n = 14) matched for age, sex, education, and handedness. Volumetric MRI scans of all subjects were obtained and the PT was measured in the right and left hemispheres. Based on these scans, subjects were classified as typical (leftward PT asymmetry) or atypical (rightward PT asymmetry). Prose passages were read at baseline, with non-altered feedback (NAF), and with DAF, and fluency was measured in these three conditions. RESULTS: At baseline the adults with developmental stuttering were significantly more dysfluent than controls (p < 0.0005). Controls' fluency did not significantly change with DAF, but DAF improved fluency in adults with developmental stuttering (p < 0.0005). In the stutter group enhanced fluency was associated with atypical (rightward) PT asymmetry, and the presence of typical (leftward) PT asymmetry was not associated with any significant change in fluency. The individuals with atypical PT asymmetry also had more severe stuttering at baseline compared to the experimental subjects with typical PT anatomy. CONCLUSIONS: In adults with persistent developmental stuttering and atypical PT anatomy, fluency is improved with DAF. These experimental subjects who showed improvement had more severe stuttering at baseline. Anomalous PT anatomy may be a neural risk for developmental stuttering in some individuals. Although a number of explanations are tenable, it may be that atypical rightward PT asymmetry may alter speech feedback, and treatment with DAF might allow these people to compensate.

Atypical cerebral laterality in adults with persistent developmental stuttering.

BACKGROUND: Two of the most consistent anatomic asymmetries found in the human brain are a larger right than left prefrontal and left than right occipital lobe. Reduced or reversed asymmetries of these regions are considered markers of atypical cerebral laterality, and atypical cerebral laterality has been proposed to increase neural risk for developmental stuttering. OBJECTIVE: S: To learn if atypical prefrontal and occipital lobe asymmetries are more common in adults who stutter vs fluent control subjects and to determine whether lobar size or asymmetry patterns are associated with stuttering severity or language abilities. METHODS: Adults with persistent developmental stuttering (n = 16) and matched control subjects (n = 16) had language and stuttering assessments. Subjects were also studied with volumetric MRI scans. Total hemisphere, prefrontal, and occipital lobe regions were measured, and volumes were calculated proportionally to hemisphere volume. RESULTS: Hemisphere and total brain volumes did not differ between the groups. Control subjects had the expected larger right than left prefrontal and larger left than right occipital lobe volume. In contrast, the adults who stutter did not have these asymmetries. Stuttering severity was not associated with specific anatomic configurations, whereas language-processing deficits in adults who stutter were associated with prefrontal and occipital volume reduction. CONCLUSIONS: Developmental stuttering is associated with atypical prefrontal and occipital lobe asymmetries. In addition, deficits in language processing were associated with some anatomic measures in the adults who stutter.

Ecological implications of ideomotor apraxia: evidence from physical activities of daily living.

OBJECTIVE: To learn if ideomotor apraxia (IMA) adversely influences skilled acts in the environment and interferes with independent functioning after stroke. METHODS: The relationship between IMA severity, based on scores from a verbal gesture-to-command (pantomime) task, and the dependency score, as defined by increased caregiver assistance on the Physical Self-Maintenance Scale (PSMS), was investigated in 10 unilateral left hemisphere-damaged stroke patients and 10 matched control subjects. RESULTS: There was a significant relationship between apraxia severity and dependency in physical functioning (PSMS). Impairment on the PSMS in the patients with IMA could not be accounted for based on overall cognitive impairment, poststroke depression, content-conceptual errors, elementary motor impairment, lesion size, or stroke-test interval. Analysis of categories composing the PSMS revealed that the patients with apraxia had increased dependency in grooming, bathing, and toileting relative to age-matched control subjects. CONCLUSIONS: These findings emphasize the ecological implications of apraxia and the need for rehabilitation strategies to improve the execution and efficiency of coordinated skilled movements in stroke patients with left hemisphere damage.

Cortical and subcortical contributions to ideomotor apraxia: analysis of task demands and error types.

Ideomotor apraxia (IMA) is often associated with damage of the dominant parietal cortex, but many other lesion sites have been implicated suggesting that the praxis system is mediated by a distributed modular network. Although IMA has been reported with subcortical lesions, the role of subcortical structures in the praxis neural network has not been fully addressed. To ascertain the role of subcortical structures in praxis, we compared praxis performance on a variety of tasks in patients with left hemisphere cortical and subcortical lesions. The cortical patients presented with deficits in the production of transitive and intransitive gestures-to-verbal command and imitation, as well as impaired gesture discrimination. In contrast, the subcortical group demonstrated mild production-execution deficits for transitive pantomimes, but normal imitation and discrimination. Qualitative error analysis of production deficits, revealed that both patient groups produced timing errors and the full range of spatial errors. Whereas the subcortical group made more postural errors than the cortical group, sequencing, unrecognizable and no-response errors were only produced by the cortical group. The different profiles of praxis deficits associated with cortical and subcortical lesions, suggests that these structures may have different roles in praxis.

Right and left handedness defined: a multivariate approach using hand preference and hand performance measures.

OBJECTIVE: The major aim of this study was to determine whether a combination of hand preference inventories and hand performance measures identifies distinct handedness groups. If distinct groups are identified, then these subgroupings can be used in future studies to learn more about the neurobiology of these distinct handedness groups. BACKGROUND: Although most individuals classify themselves as right- or left-handed, it is not entirely clear whether handedness should be determined based on preference inventories, hand performance tasks, or a combination of these measures. Given that hand preference is linked in part to hemispheric specialization of language, it is important to clearly define hand preference groups if lateralized differences between right- and left-handers are to be explored. Healthy adult right- and left-handers were examined from a multivariate perspective in an attempt to determine whether handedness subgroups exist within performance data. METHOD: Hand preference of 62 right- and left-handed male and female adults was assessed using items from Briggs and Nebes' and Oldfield's handedness inventories. Individuals were assigned to right- and left-hand preference groups, both by visually inspecting the distribution of preference scores and via cluster analysis. Asymmetries in performance of unimanual motor tasks (grooved pegboard, finger-tapping, and grip strength) were then examined using a multivariate approach. RESULTS: Sixteen items from the two-handedness inventories were used to determine preference-based handedness groups. Two non-overlapping groups, right- and left-hand preference, were identified. Writing hand was highly correlated with hand-preference group, as only three individuals in the entire sample wrote with the non-preferred hand. The expected unimodal distributions of performance asymmetry scores, known as laterality quotients (LQs), were seen. However, when those LQs were viewed from a multivariate perspective, distinct performance-based groups emerged. In more than 90% of the observed cases, the performance-based groups corresponded to preference-based groups. No sex differences were found; the relationship between preference and performance measures was not significantly different for men and women. CONCLUSIONS: Writing hand was highly correlated with scores from a hand preference inventory. In contrast, the use of a single hand performance measure, finger tapping or pegboard, did not always correctly classify an individual as right- or left-handed. However, when both of these hand performance measures were used together. individuals were correctly classified as right- or left-handed. Using this approach, two approximately non-overlapping groups, right- and left-handers, emerged. Thus, handedness is probably not a one-dimensional trait or behavior, and must be defined using multiple measures that assess different aspects of hand preference and performance. The implications for hemispheric specialization of language and neural asymmetry research are discussed.

Anomalous anatomy of speech-language areas in adults with persistent developmental stuttering.

OBJECTIVE: The major aim of this study was to determine whether adults with persistent developmental stuttering (PDS) have anomalous anatomy in cortical speech-language areas. The major postulate was that anomalous cerebral dominance, reflected by anomalous cortical anatomy in various regions, may put an individual at increased risk for the development of stuttering. METHODS: Adults with PDS (n = 16) and controls (n = 16) matched for age, sex, hand preference, and education were studied. Volumetric MRI scans were completed. Frontal (pars triangularis, pars opercularis) and temporo-parietal areas (planum temporale, posterior ascending ramus) were measured in the left and right hemispheres and interhemispheric asymmetries were computed. Gyral variants were assessed within these perisylvian cortical speech-language areas. RESULTS: The right and left planum temporale were significantly larger in the adults with PDS (p = 0.045), and the magnitude of the planar asymmetry was reduced (p = 0.003). Some gyral variants were unique to the adults with PDS, including a second diagonal sulcus and extra gyri along the superior bank of the sylvian fossa. In addition, anatomic subgroups emerged based on sex and hand preference. Overall, the adults with PDS had significantly more gyral variants (mean = 4.19) than controls (mean = 1.31, p < 0.0005). CONCLUSIONS: These results provide strong evidence that adults with PDS have anomalous anatomy in perisylvian speech and language areas. No one anatomic feature distinguished the groups, but multiple loci within a widely distributed neural network differed between groups. These results provide the first evidence that anatomic anomalies within perisylvian speech-language areas may put an individual at risk for the development of stuttering.

Swallowing physiology of sequential straw drinking.

The goal of this study was to examine deglutitive physiology during sequential straw drinking in healthy young adults (n = 15) to learn how sequential swallowing differs from single swallows. The physiology of single swallows has been studied extensively in healthy adults and in adults with a variety of debilitating conditions, but the physiology of sequential swallows has not been studied adequately. Videofluoroscopic analysis revealed three distinct patterns of hyolaryngeal complex (HLC) movement during sequential straw swallows: opening of the laryngeal vestibule after each swallow (Type I, 53%), continued vestibule closure after each swallow (Type II, 27%), and interchangeable vestibule opening and closing during the swallow sequence (Mixed, 20%). Unlike discrete swallowing, the onset of the pharyngeal swallow occurred when the bolus was inferior to the valleculae in the majority of subjects and was significantly associated with HLC movement pattern. The leading bolus edge was inferior to the valleculae at swallow onset for Type II movement patterns. For Type I movement patterns, bolus position at swallow onset was randomly distributed between three anatomical positions: superior to the valleculae, at the level of the valleculae, and inferior to the valleculae. Preswallow pharyngeal bolus accumulation, which is common during mastication, was evident and significantly associated with the HLC pattern of opened laryngeal vestibule after each swallow. These data suggest that in healthy young adults, sequential swallows differ physiologically from discrete swallows and indicate substantial variability in deglutitive biomechanics.

Praxis lateralization: errors in right and left hemisphere stroke.

Whereas the representations of skilled movements in most right handers are stored in the left hemisphere, the right hemisphere's contribution to action planning remains unclear. We investigated error patterns in left (LHD) and right hemisphere damaged (RHD) subjects as well as normal control subjects (C) to determine if specific components of action programs may be processed by the right hemisphere or bilaterally represented. We had these subjects perform gestures to verbal command with the ipsilesional limb. Although the LHD group made significantly more qualitative errors than the C and RHD groups, the RHD subjects produced a number of apraxic errors. Specifically, the LHD group produced a wide range of spatiotemporal and conceptual errors for both transitive and intransitive gestures, while the RHD group made specific spatial and temporal errors primarily when performing transitive gestures. These findings support the postulate that the left hemisphere stores the spatiotemporal and conceptual representations of learned skilled movements, while several specific components of action programs, such as external configuration (limb orientation) and timing, may have bihemispheric representations.

Dual-task performance in right- and left-handed adults: a finger-tapping and foot-tapping study.

The dual-task paradigm has been used extensively to study laterality, with concurrent verbalization interfering with right finger-tapping in right handers. Only a few studies have used this paradigm to study interference patterns in left handers and have found inconsistent results. The dual-task paradigm has not been used to study interference effects with concurrent verbalization and foot-tapping. The objective of this study was to use this paradigm to assess whether verbal interference produces different effects on finger- and foot-tapping rate for right handers as compared to left handers. 12 right-handed and 12 left-handed men were studied, each with uncrossed hand and foot dominance, i.e., all individuals were either right handed and right footed or left handed and left footed. Subjects performed finger- and foot-tapping tasks with and without verbal interference. A significant relationship was found between handedness and finger- and foot-tapping rate; individuals with a stronger right-hand preference tended to tap at a higher rate on the right side and vice-versa. Analogous relationships were not found when participants were tapping and speaking concurrently. With verbal interference, both right and left handers had a significant asymmetric effect with a decremental response in right finger-tapping rate and a facilitative effect on left finger-tapping rate. In contrast, there was a bilateral decremental response in foot-tapping with verbal interference in both right and left handers. The implications of these findings are discussed with reference to cerebral laterality of language systems and to the differential organization and integration of the motor representations of the hand and the foot.

Morphology of the frontal operculum: a volumetric magnetic resonance imaging study of the pars triangularis.

OBJECTIVE: Broca's area, which includes the pars triangularis (PTR), is a neuroanatomical region important in speech and language production. Linear measures of the PTR have been found to be asymmetric, with the direction of the asymmetry correlating with language dominance determined by Wada testing. It is unclear, however, whether these linear measurements correlate with volumetric measures, and it is also unknown whether white matter and/or gray matter contribute differentially to these asymmetries. To investigate these issues, volumetric magnetic resonance imaging methodologies were used to measure the PTR in a group of healthy right-handed men (n = 12). There was a significant leftward asymmetry of the PTR using linear and volumetric measures. Linear measures of the left and right hemispheres were highly correlated with volumetric measures. Underlying gray and white matter both contributed to PTR asymmetry. Anatomical boundaries and four configurations (V, U, Y, and J) are discussed with reference to potential interhemispheric differences.

Clinical predictors of dysphagia and aspiration risk: outcome measures in acute stroke patients.

OBJECTIVE: To use an established dysphagia clinical screening system to evaluate outcomes in acute stroke patients. DESIGN: Case-control study. SETTING: Tertiary care center. PARTICIPANTS: Acute stroke patients (n = 56) consecutively referred to a speech pathology service. MAIN OUTCOME MEASURES: Outcomes (ie, pneumonia, dietary status at discharge) in patients who were referred for a videofluoroscopic swallow study (VSS) based on results of a previously validated clinical screening system were compared with outcomes in patients who were not referred for VSS based on the clinical evaluation. RESULTS: Thirty-eight of 56 patients (68%) presented with 2 or more clinical predictors of moderate to severe dysphagia and were further evaluated with VSS, whereas 18 patients (32%) had fewer than 2 clinical features and were not evaluated radiographically. Based on patient outcomes and VSS results, identification of at least 2 clinical predictors significantly distinguished patients with moderate to severe dysphagia from patients with mild dysphagia or normal swallowing. None of the patients in either group developed pneumonia while following recommendations of the clinical or dynamic swallowing evaluation, and 93% of the patients returned to a regular diet. CONCLUSIONS: These data demonstrate that clinical use of this screening system can objectively identify acute stroke patients who warrant further diagnostic studies and can safely determine which patients need no further deglutitive evaluation.

Neuroacanthocytosis masquerading as Huntington's disease: CT/MRI findings.

Neuroacanthocytosis (NA) is a rare, degenerative, presumably autosomal-recessive disorder of the nervous system presenting in adulthood and is associated with acanthocytosis of the peripheral blood. The clinical spectrum of NA shares similarities with Huntington's disease (HD), including dyskinetic choreiform movements and degeneration of the caudate nucleus. A woman presented with choreiform movements and was given a presumed diagnosis of HD. Neuroimaging studies were consistent with HD. She lacked the genetic marker for HD, and further evaluation revealed acanthocytosis of the peripheral blood. The case illustrates the similarities and differences in the clinical presentations and neuroimaging studies of these two disease entities, emphasizing the need for a careful clinical evaluation.

Ideomotor apraxia in Alzheimer disease and left hemisphere stroke: limb transitive and intransitive movements.

OBJECTIVE: Ideomotor apraxia was studied in patients with Alzheimer disease (AD) and unilateral left hemispheric damaged (LHD) stroke to determine whether these groups differed. BACKGROUND: Given that the neuropathology of AD is bilateral and more diffuse than the localized involvement in patients after an LHD stroke, and given that the cognitive deficits in AD are more widespread than in LHD stroke, the authors predicted that patients with these disorders would differ in response to an auditory command task administered to evaluate ideomotor apraxia, and that the two patient groups would be significantly more impaired than healthy matched control subjects. METHODS: Twenty-one persons were studied, including equal numbers of patients with AD, patients with unilateral LHD stroke, and control subjects. An auditory command test of limb apraxia was administered and videotaped to score performance and to code spatial-temporal or content errors. RESULTS: The patients with AD and LHD stroke were significantly more impaired than healthy control subjects. Whereas the patients with AD and LHD stroke were equally apraxic and did not differ in their performance of transitive limb movements, the patients with AD were significantly more impaired than the patients with stroke when performing intransitive limb movements. A positive correlation was found between severity of dementia and severity of apraxia in the patients with AD. The patients with LHD stroke were as likely to make spatial-temporal as content errors when performing intransitive limb movements, whereas the patients with AD made content errors only. Error types produced with transitive limb movements did not differ between groups; spatial-temporal errors were the most common errors made both by patients with AD and patients with LHD stroke. CONCLUSIONS: As predicted, patients with AD and with LHD stroke were impaired when producing limb movements after auditory command, and both patient groups were significantly more impaired than the healthy adults. Patients with AD were significantly more impaired than patients with stroke when performing intransitive limb movements, and error types differed by group. Patients with AD and patients with stroke were equally impaired when performing transitive movements, and error types did not differ by group. Patients with ideomotor apraxia are often degraded in their production of transitive and intransitive movements, and the observation that performance may differ depending on the type of limb movement suggests that movement representations for transitive and intransitive movements may be at least partially independent.

Apraxia and motor-skill acquisition in Alzheimer's disease are dissociable.

Many patients with Alzheimer's disease (AD) are apraxic and the apraxia has been posited to be related to a loss of movement representations. Whereas patients with Alzheimer's disease have been reported to demonstrate normal motor learning on a rotor pursuit skill acquisition task, it is unknown whether AD subjects who are apraxic demonstrate normal skill-learning. We tested subjects with probable AD and normal controls on a rotor pursuit task. We also tested the AD subjects for ideomotor apraxia. Subjects with AD who were apraxic had normal motor learning. In addition, praxis score did not correlate with performance on the skill-acquisition task. The results suggest that ideomotor praxis and motor learning are at least partly dissociable.

Lesion localization in acute stroke patients with risk of aspiration.

The objective of this prospective study was to determine whether specific neuroanatomical sites were associated with increased risk of aspiration in acute stroke patients. Videofluoroscopic swallow studies (VSS) and computed tomography or magnetic resonance imaging scans were completed on consecutive male stroke patients (n = 54). Videofluoroscopic swallow studies were scored on a scale from 0 (normal swallowing) to 4 (severe dysphagia). Patients with scores of 0-1 were grouped together as having no risk of aspiration, and patients with scores of 2-4 were grouped together as having a risk of aspiration. Lesion analyses revealed that location appeared to be more critical than hemisphere or lesion size in predicting patients at risk of aspiration. Anterior locations and subcortical periventricular white matter sites were commonly lesioned in patients with risk of aspiration, whereas patients without risk of aspiration were more likely to have posterior lesions and lesions to subcortical gray matter structures. These data demonstrate that swallowing appears to be mediated by a distributed neural network that involves both cerebral hemispheres with descending input to the medulla; however, specific lesion locations may put patients at a greater risk of aspiration.

Hemispheric and sex-linked differences in Sylvian fissure morphology: a quantitative approach using volumetric magnetic resonance imaging.

OBJECTIVE: In a sample of right-handed adults, volumetric magnetic resonance imaging (MRI) was used to reinvestigate hemispheric and sex-linked differences in Sylvian fissure (SF) morphology. BACKGROUND: Asymmetries of the SF exist with a predominant leftward asymmetry consistently reported in postmortem studies. These anatomic asymmetries may reflect asymmetric allocation of adjacent opercula, with some investigators positing a relationship with planum temporale asymmetries, as the postcentral SF is more asymmetric than the anterior segment. Sex-related differences have also been reported with reduced asymmetries in women relative to men. METHOD: Using in vivo MRI surface renderings, SF asymmetries were studied in a group of consistently right-handed men (n = 12) and women (n = 12). Anterior and postcentral SF lengths were measured. RESULTS: Overall, there was a significant leftward asymmetry of the horizontal SF (anterior and postcentral) in men and women. Whereas there was a significant leftward asymmetry of the postcentral SF, there was no significant asymmetry of the anterior SF. There was an increase in the parietal operculum anterior to the posterior ascending ramus (PAR) in the left hemisphere and posterior to the PAR in the right hemisphere when SF asymmetries were leftward, with the length of the anterior parietal operculum positively correlated with postcentral SF length. CONCLUSIONS: These findings demonstrate that the SF is asymmetric but that clear sex-related effects do not exist in consistently right-handed subjects.

Lingual discoordination and dysphagia following acute stroke: analyses of lesion localization.

The mechanism and neural substrates that mediate lingual coordination during swallowing have not been well characterized. Although lingual discoordination during swallowing has been difficult to quantify, it has been defined as the random disorganization of anterior-posterior tongue movements evident in bolus propulsion. In a sample of consecutive acute stroke patients (n = 59), videofluoroscopic evaluation showed a 19% incidence of lingual discoordination during swallowing. Lingual discoordination during swallowing was not commonly associated with buccofacial apraxia, apraxia of speech, nor limb apraxia. Hemisphere and anterior-posterior localization did not predict occurrence of lingual discoordination. Lingual discoordination during swallowing occurred commonly in patients with subcortical lesions with the periventricular white matter (PVWM), the most common site of involvement. PVWM lesions may disconnect anterior and posterior cortical regions that are critical to oral control and coordination in swallowing, thereby producing lingual discoordination during swallowing. These data also suggest that the neural mechanisms that mediate lingual coordination may at least in part be independent of the neural systems that mediate buccofacial, limb, and speech praxis functions.

Cognitive and emotional sequelae of cerebellar infarct: a case report.

The cerebellum has long been the subject of scientific investigation, but its role in nonmotor functions has only recently begun to receive serious consideration. Despite the growing literature linking the cerebellum to nonmotor/cognitive functions in humans, some controversy remains concerning the cerebellum's role in these processes. We present a patient who developed both specific language processing and verbal memory deficits and emotional changes in the context of normal intelligence following a bilateral cerebellar ischemic stroke. Despite having multiple localized cerebellar lesions, this patient had no significant motor problems, nor was there radiological evidence of focal forebrain lesions to which the cognitive and emotional effects might be attributed. The role of the cerebellum in cognition and the relevance of cerebellum-associated cognitive/emotional dysfunction to the practicing clinician are discussed.

Age-related changes of the insular cortex and lateral ventricles: conventional MRI volumetric measures.

Preliminary data suggest that the insular region may be atrophied in patients with Alzheimer's disease when compared with healthy, age-matched control subjects. Therefore, normative data on age-related changes of the insular cortex were gathered and compared with age-related changes in the bodies of the lateral ventricles, which have been studied previously. Cerebrospinal fluid (CSF) volume of the lateral ventricles and insular cortical regions were measured on T1-weighted axial magnetic resonance images in 93 healthy subjects (age 21 to 84 years). Age-related changes were found in the lateral ventricles (r = 0.57, p < 0.0001) and in the CSF insular space (r = 0.42, p < 0.0001). Increasing age accounted for a significant amount of the variance for the lateral ventricle (pc = 0.45, p < 0.0001), but not for the insula (pc = 0.15, p = 0.14). Although there was a continuous linear increase in lateral ventricular volume with age, the CSF insular space increased linearly until the fourth decade, then plateaued until the seventh decade, with a linear increase thereafter. These data suggest that age-related changes occur in the region of the insular cortex, but differ from age-related changes of the lateral ventricles.

MRI asymmetries of Broca's area: the pars triangularis and pars opercularis.

Broca's area, which includes the pars triangularis (PTR) and pars opercularis (POP), is a neuroanatomic region important in speech-language production. Previous data demonstrated that PTR asymmetries are highly correlated with language dominance determined by selective hemispheric anesthesia or Wada testing, suggesting that asymmetries of the PTR may, in part, predict language dominance. The POP, however, has not been measured on volumetric magnetic resonance imaging (MRI), and therefore, it is unclear whether morphological asymmetries of the POP exist, and whether these asymmetries differ in right- and left-handers. The purpose of this study was to determine if measurable asymmetries of the POP exist on MRI, and whether the direction of the asymmetries differ in right- and left-handers. The PTR and POP were measured on volumetric MRI scans of 16 right-handers and 16 left-handers matched for age and gender. There was a significant leftward asymmetry of the PTR in right- and left-handers, although the asymmetry was reduced in the left-handers. In contrast, there was a leftward asymmetry of the POP in right-handers, and a rightward asymmetry in the left-handers. Handedness, derived from a handedness inventory, was positively correlated with POP asymmetry.