David M. Corey

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.

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. Objectives: 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.

On the bias of Huffcutt and Arthur's (1995) procedure for identifying outliers in the meta-analysis of correlations

This study documents how the use of A. I. Huffcutt & W. A. Arthurs (1995) sample adjusted meta-analytic deviancy (SAMD) statistic for identifying outliers in correlational meta-analyses results in inaccuracies in mean r. Monte Carlo simulations found that use of the SAMD resulted in the overidentification of small relative to large correlations as outliers. Furthermore, this tendency to overidentify small correlations was found to increase as the magnitude of the population correlation increased and resulted in mean rs that overestimated the population correlation. The implications for meta-analysts are discussed, and 2 possible solutions are offered.

Swallowing Lateralization: The Effects of Modified Dual-Task Interference

A modified dual-task paradigm was designed to learn whether swallowing functions are selectively mediated by the left or right hemisphere. Healthy right-handed men (N = 38) were studied using videofluoroscopy to examine continuous straw drinking at baseline and with three interference conditions (silent word repetition, line orientation, finger tapping). Results indicate that activation of both right and left hemispheres can interfere with some swallowing behaviors. Findings suggest possibly different roles of the two hemispheres in the mediation of swallowing and support the notion that specific components of swallowing may be preferentially mediated by the left versus the right hemisphere.

Variability in perisylvian brain anatomy in healthy adults.

Gray matter volumes of Heschls gyrus (HG), planum temporale (PT), pars triangularis (PTR), and pars opercularis were measured on MRI in 48 healthy right-handers. There was the expected leftward PT asymmetry in 70.8%, and leftward PTR asymmetry in 64.6% of the sample. When asymmetry patterns within individuals were examined, there was not one typical pattern, rather several typical configurations were found. In addition, some combinations of asymmetry did not exist in our sample suggesting that some perisylvian anatomical configurations may provide a more suitable neural substrate for the development of language than others. There were also sex differences in HG. Men had rightward asymmetry and women demonstrated leftward asymmetry, due to women having smaller right HG, compared to men.

Relevance of Subcortical Stroke in Dysphagia

Background and Purpose— Unilateral cortical lesions are associated with dysphagia in ischemic stroke. It is unclear, however, whether acute subcortical stroke is associated with a similar risk of dysphagia. The aim of this study was to determine the occurrence of dysphagia in purely subcortical stroke and identify dysphagia characteristics. Methods— Between 2003 and 2005, videofluoroscopic swallow studies (VFSSs) were completed in 20 consecutive ischemic stroke patients with purely subcortical lesions (right hemisphere damage [RHD]=10, left hemisphere damage [LHD]=10) and 25 age-matched controls. Individuals were classified with dysphagia when at least 2 swallowing measures were 2 standard deviations above mean scores for the control group. Lesion volume, hemisphere, and location were determined from diffusion-weighted magnetic resonance imaging scans. Results— Seven subcortical stroke patients (35%) met VFSS criteria for dysphagia (LHD=5, RHD=2); 4 patients presented with clinically significant dysphagia. A significant interaction between hemisphere and lesion location was identified. Whereas 3 of 5 patients with dysphagia (60%) had lesions to the left periventricular white matter (PVWM), LHD patients without dysphagia did not have PVWM lesions. In contrast, no RHD patients with PVWM lesions had dysphagia, and 6 of 8 patients without dysphagia (75%) had PVWM lesions. Oral transfer was significantly slower in patients with subcortical stroke compared with the healthy adults. Conclusions— Lesions to the left PVWM may be more disruptive to swallowing behavior than similar lesions to the right PVWM. Swallowing deficits involving oral control and transfer may be a marker of subcortical neural axis involvement.

Dysphagia in Stroke: Development of a Standard Method to Examine Swallowing Recovery

This study began development of a standard method that uses the videofluoroscopic swallow study for evaluation of swallowing recovery after stroke based on a definition of dysphagia derived from three domains: bolus timing, bolus direction, and bolus clearance. Two experiments were conducted: one that defined normal versus disordered swallowing based on the range of scores in a sample of healthy adults (n = 13), and one that applied these thresholds to nine stroke patients to identify the presence of dysphagia. Results indicate that acute and protracted dysphagia may be more accurately detected by identifying abnormalities on multiple objective measures of swallowing rather than on laryngeal penetration or aspiration alone. Results indicate that our selected measures and use of healthy control subjects to establish normal thresholds may eventually contribute to the definition and differentiation of dysphagic and nondysphagic patients. Further research with a broader sample of healthy controls and stroke patients is mandatory.

Verbal dichotic listening in right and left-handed adults : Laterality effects of directed attention

Dichotic listening performance of consonant vowel stimuli was studied in 51 adult right- and left-handers in three attention conditions: non-directed and directed to either the right or left ear. In the non-directed condition, a significant right-ear advantage was found in both handedness groups with a stronger asymmetry in right-handers. There are at least three explanations for this ear bias. The classic or structural hypothesis suggests that to the right ear projects more strongly to the language dominant left hemisphere. The callosal relay hypothesis is based on the influence of inhibitory connections via the corpus callosum. The attentional hypothesis suggests that each hemisphere primarily directs attention to contralateral space and because the left hemisphere is dominant for language in both groups, and is aroused by speech stimuli, attention is primarily directed to the right ear. Neither hypothesis can explain why greater than 95% of right-handers have left hemisphere language dominance, but only 70-80% have a right ear bias. Our results demonstrate that in the directed attention conditions both groups increased their lateral biases when directed to either the right or left. The classic or structural hypothesis cannot account for these changes, thereby providing support for the attentional hypothesis. In addition, the right-handed subjects exhibited a greater shift of bias than did the left-handed subjects, when directing their attention leftward. This finding suggests that right-handed people are better able to shift their attention than left-handed people.

Sex-linked differences in the anatomy of the perisylvian language cortex: a volumetric MRI study of gray matter volumes.

Perisylvian regions important for auditory processing include Heschls gyrus (HG), the planum temporale (PT), the posterior superior temporal gyrus (pSTG), and the posterior ascending ramus (PAR). Sex-linked differences in language functions and anatomy have been suggested. To examine sex-linked differences, the authors used MRI to measure HG, PT, pSTG, and PAR volumes. Sex differences were found in right HG and right pSTG volumes but not in the left volumes of these structures. For the PT, there were sex differences in asymmetry; women exhibited leftward asymmetry of the PT, whereas men did not exhibit PT asymmetry. These findings suggest that there are sex-linked differences in the anatomy of primary and association auditory cortices.