Cerebral laterality in adolescent major depression

This study tests the hypothesis that adolescents with major depression exhibit abnormalities in cerebral asymmetry previously found among adults. Perceptual asymmetry was assessed through tests of verbal and non-verbal dichotic listening in four groups - 48 adolescents with major depression, 22 adolescent comparisons with no history of Axis I disorders, 149 adults with major depression, and 57 comparison adults with no history of Axis I disorders. Data from adults have been previously reported. In both age groups, subjects with major depression were further divided based on the presence or absence of an anxiety disorder. Procedures used to collect perceptual asymmetry data in adolescents and adults were identical. In both age groups, depressed and healthy subjects showed perceptual asymmetry in expected directions for verbal and non-verbal dichotic tasks. Depressed and comparison subjects differed in performance on the Fused-Word Test, though these differences varied as a function of anxiety and developmental level. Relative to comparisons, both adolescents and adults with major depression exhibited an increased right ear/left hemisphere advantage for fused words. Adults but not adolescents with comorbid major depressive and anxiety disorders exhibited a reduced right ear/left hemisphere advantage for fused words. These findings suggest similarities and differences across development in the relationship between cerebral laterality and psychopathology. Further studies using longitudinal and family-based designs, as well as various measures of regional brain activity, are needed to enhance understanding of associations between cerebral laterality and psychopathology across development.     

Abnormal functional brain asymmetry in depression: evidence of biologic commonality between major depression and dysthymia

Prior studies have found abnormalities of functional brain asymmetry in patients having a major depressive disorder (MDD). This study aimed to replicate findings of reduced right hemisphere advantage for perceiving dichotic complex tones in depressed patients, and to determine whether patients having "pure" dysthymia show the same abnormality of perceptual asymmetry as MDD. It also examined gender differences in lateralization, and the extent to which abnormalities of perceptual asymmetry in depressed patients are dependent on gender. Unmedicated patients having either a MDD (n=96) or "pure" dysthymic disorder (n=42) and healthy controls (n=114) were tested on dichotic fused-words and complex-tone tests. Patient and control groups differed in right hemisphere advantage for complex tones, but not left hemisphere advantage for words. Reduced right hemisphere advantage for tones was equally present in MDD and dysthymia, but was more evident among depressed men than depressed women. Also, healthy men had greater hemispheric asymmetry than healthy women for both words and tones, whereas this gender difference was not seen for depressed patients. Dysthymia and MDD share a common abnormality of hemispheric asymmetry for dichotic listening.     

On the nature of the cortical function underlying right hemisphere auditory perception

The nature of the function underlying the right hemisphere superiority in processing some types of auditory stimuli was examined by investigating the relationship between the degree of functional asymmetry observed during dichotic testing and the harmonic information conveyed in the test stimuli. Ninety-six right handed subjects received one of four dichotic pitch recognition tests. The tests differed from one another in the number of constituent overtones present in the tonal stimuli. As stimuli increased in complexity from pure tones to square waves, the overall accuracy of pitch discriminations increased and a right hemisphere advantage emerged for both accuracy and latency of response. These results indicate that right hemisphere auditory function is specialized for the analysis of steady state harmonic information rather than for music perception per se.     

Electroencephalographic and perceptual asymmetry differences between responders and nonresponders to an SSRI antidepressant.

BACKGROUND: Recent reports suggest the value of electroencephalographic and dichotic listening measures as predictors of response to antidepressants. This study examines the potential of electroencephalographic alpha asymmetry and dichotic measures of perceptual asymmetry as predictors of clinical response to 12 weeks of treatment with fluoxetine (Prozac). METHODS: Resting electroencephalography (eyes open and eyes closed) and dichotic listening with word or complex tone stimuli were assessed in depressed outpatients during a pretreatment period. RESULTS: Fluoxetine responders (n = 34) differed from nonresponders (n = 19) in favoring left over right hemisphere processing of dichotic stimuli. They also differed in their resting electroencephalographic alpha asymmetry, particularly in the eyes open condition. Nonresponders showed an alpha asymmetry indicative of overall greater activation of the right hemisphere than the left, whereas responders did not. The relationship between hemispheric asymmetry and treatment response interacted with gender, being evident among depressed women but not men. CONCLUSIONS: The results are consistent with the hypothesis that a characteristic tendency toward greater left than right hemisphere activation is associated with favorable response to fluoxetine, whereas the opposite hemispheric asymmetry predicts poor response.     

Brain laterality,depression and anxiety disorders: New findings for emotional and verbal dichotic listening in individuals at risk for depression

ABSTRACT

Studies using dichotic listening tests and electroencephalographic (EEG) measures of hemispheric asymmetry have reported evidence of abnormal brain laterality in patients having depressive disorders. We present new findings from a multigenerational study of risk for depression, in which perceptual asymmetry was measured in dichotic listening tests of emotional and verbal processing. Biological offspring and grandchildren of probands with a major depressive disorder (MDD) who were at high risk and those of nondepressed controls who were at low risk were tested on dichotic emotional recognition and consonant–vowel syllable tests. In the emotion test, individuals with a lifetime diagnosis of MDD had a smaller right hemisphere advantage than those without a MDD, but there was no difference between high- and low-risk groups or between those with or without an anxiety disorder. In the syllable test, a smaller left hemisphere advantage was found in individuals with an anxiety disorder compared to those without an anxiety disorder, but there was no difference between high- and low-risk groups or between those with or without a MDD. This double dissociation indicates that lifetime diagnosis of MDD and anxiety disorders have a differential impact on lateralized hemispheric processing of emotional and verbal information.     

Hemispheric specialization for language in children with different types of specific language impairment

The aim of the study was to investigate whether children with Specific Language Impairment (SLI) show reduced left hemisphere specialization for language and, if so, whether it is associated with a deficit in phonological encoding and a specific type of SLI (Mixed Receptive-Expressive, Expressive, Phonological). We adopted two dichotic listening paradigms, which differed in the phonological similarity of the presented words (Fused and Non-Fused dichotic words tests), as well as a phonological working memory test. Participants included 34 pre-school and school age children affected by SLI. On the dichotic tests, as a group the children with SLI showed a reduced pattern of left hemisphere specialization for language compared to age-matched normal children, with significant differences only in the Fused condition. However, the pattern of hemispheric specialization varied depending on the type of SLI, with reduced left hemisphere specialization in the Expressive type and, to a lesser extent, in the Phonological type of SLI, but not in the Receptive-Expressive type. The three subgroups also differed in phonological processing abilities and the incidence of a positive family history for language disorders: the Receptive-Expressive group performed worse on the working memory and dichotic tests and the Expressive and Phonological groups presented high frequency for familial language disorder. These results suggest that different subtypes of SLI are not different manifestations of the same underlying disorder, but represent pathological conditions that have distinct markers both at the behavioral and neurofunctional level.     

Left hemisphere dysfunction during verbal dichotic listening tests in patients who have social phobia with or without comorbid depressive disorder

OBJECTIVE: Behavioral, electrophysiological, and imaging studies have found evidence that anxiety disorders are associated with left hemisphere dysfunction or higher than normal activation of right hemisphere regions. Few studies, however, have examined hemispheric asymmetries of function in social phobia, and the influence of comorbidity with depressive disorders is unknown. The present study used dichotic listening tests to assess lateralized cognitive processing in patients with social phobia, depression, or comorbid social phobia and depression. METHOD: The study used a two-by-two factorial design in which one factor was social phobia (present versus absent) and the second factor was depressive disorder (present versus absent). A total of 125 unmedicated patients with social phobia, depressive disorder, or comorbid social phobia and depressive disorder and 44 healthy comparison subjects were tested on dichotic fused-words, consonant-vowel syllable, and complex tone tests. RESULTS: Patients with social phobia with or without a comorbid depressive disorder had a smaller left hemisphere advantage for processing words and syllables, compared with subjects without social phobia, whereas no difference between groups was found in the right hemisphere advantage for processing complex tones. Depressed women had a larger left hemisphere advantage for processing words, compared with nondepressed women, but this difference was not seen among men. CONCLUSIONS: The results support the hypothesis that social phobia is associated with dysfunction of left hemisphere regions mediating verbal processing. Given the importance of verbal processes in social interactions, this dysfunction may contribute to the stress and difficulty experienced by patients with social phobia in social situations.     

抑郁症患者脑功能偏侧化的分听研究

目的 探讨抑郁症患者大脑半球机能不对称的特点,以及抗抑郁药治疗后半球机能不对称性的变化。方法 用集中注意法及两种押韵词,对115例抑郁症患者进行耳优势测试,其中34例在服药6周后再次测定;并与58例健康者进行对照分析。结果 健康组真词测听未见耳优势而假词测听则呈现右耳(左半球)优势;抑郁症组真词测听未见耳优势而假词测听呈增强的右耳(左半球)优势;服药前后抑郁症患者的大脑半球机能不对称性无变化。结论 抑郁症组对汉字词的加工与认知,表现出较健康组强的右耳(左半球)优势;患者的言语偏侧化指数与症状严重程度无相关性;假词为较为理想的分听材料。     

Increasing the power of dichotic methods: The fused rhymed words test

A dichotic test made up of monosyllabic rhymed CVC words was modified to minimize stimulus dominance and errors and then administered to 194 dextrals and 175 sinistrals in four different laboratories. The proportion of subjects with left ear advantages in both the right and left-handed groups closely approximated that expected from neurologic data. This dichotic test appears to reflect hemispheric specialization for language function more accurately than previously available tests. Further direct validation studies are needed, however, comparing direction of ear asymmetry and other indices of hemispheric specialization for language on a subject by subject basis.     

Emotion words are remembered better in the left ear

In dichotic listening studies, numerous investigators have shown a left ear advantage (i.e., right hemisphere superiority), when judging emotional tone of speech. In the present study, dichotic word-pairs of emotion and non-emotion words were presented to participants who were instructed to recall the entire list in each block. Unlike other studies in which participants responded to emotional intonations, participants in the present investigation listened to stimuli that were spoken in a neutral intonation. A total of 62 participants listened to emotion (e.g., loving) and non-emotion (e.g., combine) words that were dichotically presented. The results showed a left ear advantage for emotion words. This finding provides strong support for the right-hemisphere hypothesis in the form of a stronger memory for emotion words presented to the left ear. The findings are consistent with the role of the right hemisphere in the perception of emotional information.     

Emotional language is all right: Emotional prosody reduces hemispheric asymmetry for linguistic processing

ABSTRACT

In an influential paper, Bryden and MacRae [(1989). Dichotic laterality effects obtained with emotional words. Neuropsychiatry, Neuropsychology, and Behavioral Neurology, 1, 171–176] introduced a dichotic listening task that allowed for the assessment of linguistic and prosodic processing asymmetries using the same stimuli. The task produces a robust right ear advantage (REA) for linguistic processing (identifying a target word), and a left ear advantage for emotional processing (identifying a target prosody). Here, we adapted this paradigm to determine whether and how the presence of emotional prosody might modulate hemispheric asymmetry for linguistic processing. Participants monitored for a target word among dichotic stimuli consisting of two different words, but spoken in the same emotional prosody—neutral, angry, happy, sad, or fearful. A strong REA was observed when the words were spoken in neutral prosody, which was attenuated for all the emotional prosodies. There were no differences in the ear advantage as a function of valence or discrete emotion, indicating that all emotions had similar effects. Findings are consistent with the hypothesis that the right hemisphere is better able to process speech when it carries emotional prosody. Implications for understanding of right hemisphere language functions are discussed.     

Hemisphere differences in conditional learning: an ERP-study.

The present ERP-experiment investigated brain asymmetry in encoding and representation of the formation of conditional associations in a Pavlovian framework. Two consonant-vowel syllables were used as conditional stimuli, one of them paired with an unconditional noise during the acquisition phase (CS+), the other never paired with noise (CS-). During a subsequent test phase, both CS cues were presented dichotically i.e. at the same time. Half of the subjects had the CS+ probe presented to the right ear (contralateral to the left hemisphere). The other half of the subjects had the CS+ presented to the left ear (contralateral to the right hemisphere). ERPs from F3, Fz and F4 leads were recorded. The paradigm used was an adaptation of the standard dichotic listening technique for the study of learned associations. The results showed that conditional associative learning occurred during the acquisition phase in both "groups". The P235 latency was furthermore delayed over the left hemisphere to the CS+ probe. During the dichotic test phase, there was a clear laterality or asymmetry effect between the groups for both the N125 and N450 components, possibly supporting an interpretation of asymmetry in encoding and cortical representation of a conditional association, although alternative interpretations remain open.     

Perceptual asymmetry in schizophrenia and affective disorder: implications from a right hemisphere task

The patterns of perceptual asymmetry exhibited by normal, schizophrenic, and affectively-disordered subjects on a dichotic tonal discrimination task, were compared. Affectively-disordered subjects' performances differed significantly from those of normal subjects, with normals demonstrating the expected left ear advantage, and affectively-disordered subjects showing no lateral advantage. The performance of the schizophrenic subjects fell between those of the normal and affective groups along a laterality continuum, with paranoid schizophrenic subjects tending to show a larger left ear advantage than non-paranoid schizophrenic subjects. The results do not support the hypothesis that schizophrenic subjects inappropriately transfer processing of right hemisphere stimuli to the left hemisphere, but do suggest that subgroup distinctions may be relevant to hypotheses of lateralized dysfunction in schizophrenia. Further, the performance of the affective group supports previous findings of right hemisphere abnormalities in affective disorder.     

Age effects in identifying and localising dichotic stimuli: a corpus callosum deficit?

In the present study, dichotic listening performance of 31 older adults was compared with performance of 25 younger adults under free and focused attention conditions. In addition to an age-related general decrease in performance, we observed in the focused attention condition increased asymmetry in the elderly group: the decrease of recall performance was stronger for the left ear (LE) then for the right ear (RE), while the increase of localisation errors were greater for the RE than for LE. Identifying and localising digits appear to be different process mediated predominantly by the left and right hemisphere, respectively. Since age-related reduced performance is strongest for the ear ipsilateral to the hemisphere dominant to that particular function, these finding may be ascribed to decline of corpus callosum functioning resulting in decrease interhemispheric interaction rather than to a selective decline of right hemisphere functions.     

Handedness effects in the detection of dichotically-presented words and emotions

Left-handed and right-handed subjects were given two dichotic listening tasks using identical material. In one task, they were asked to determine whether or not a specific target word was present (verbal task). In the other task, subjects were asked to indicate whether or not one of the dichotically-competing words was spoken in a particular affective tone (emotion task). Overall, a right-ear advantage (REA) was found with the verbal task and a left-ear advantage (LEA) with the emotion task. Left-handers showed a slightly smaller REA than right-handers on the verbal task, but a slightly larger LEA on the emotion task. This finding suggests that left- and right-hemispheric functions are not related in a complementary fashion and that handedness effects for nonverbal tasks are different from those seen with verbal tasks. The emotional LEA was much larger for angry stimuli than for happy, sad, or neutral stimuli. Rather than providing evidence for a hemisphere by affective valence interaction, such results suggest a stimulus-specific effect.     

Atypical brain laterality in adults with ADHD during dichotic listening for emotional intonation and words

Few studies directly examined the nature of hemispheric specialization and interaction in ADHD. The present experiment investigated left/right brain dynamics in unmedicated right handed adults with ADHD (n = 19) and in controls (n = 19), using a dichotic listening task to assess hemispheric differences in word and emotion recognition. We also assessed how focusing attention on a single ear modulated lateralized performance and affected cross-callosal interference effects. Analysis of variance indicated that ADHD subjects showed reduced left hemisphere specialization, were better at processing emotions, and worse at processing words compared to controls. These differences were eliminated during focused attention. Finally, during presumed right hemisphere processing of linguistic stimuli, subjects with ADHD showed reduced left hemisphere interference. We concluded that ADHD subjects demonstrated greater right hemisphere and reduced left hemisphere contribution during this task relative to controls. We posit that these hemispheric differences were due to management or use of available cognitive resources rather than inherent capacity.     

Behavior disorders and laterality of cerebral function

A dichotic listening test was employed to test the hypothesis that behavior disorders might have an abnormal laterality patterns of cerebral function. Eighteen behavior disorder out-patients of the psychiatry department at an university hospital and seventeen normal subjects were requested to recall dichotically presented words. The results showed that compared with the normal controls, the subjects with behavior disorders yielded less prominent right ear advantage, lesser response ear alternations, but better overall performances. The results do not support the hypothesis of the left hemisphere dysfunction in behavior disorders but suggest the possibility of the right hemisphere dysfunction.     

Is panic disorder linked to cognitive avoidance of threatening information?

We used a directed-forgetting paradigm to investigate whether panic disorder patients cognitively avoid threatening information. To determine if hemispheric laterality predicts processing biases in this paradigm, we used dichotic listening methods to ascertain participants' auditory perceptual asymmetry (PA). Panic disorder patients and healthy control participants viewed a series of intermixed threat, positive, and neutral words, each followed by an instruction to either remember the word or forget it. They then performed free recall and recognition tests for all words, irrespective of initial instructions. Directed-forgetting effects occurred equally for all word types: both groups recalled remember-words better than forget-words. Because this task is strongly affected by encoding style, panic patients as a group do not seem to avoid encoding threat cues. However, PA analyses revealed that cognitive avoidance of threat forget-words was significantly associated with greater left hemisphere bias in the control group and nonsignificantly associated with lesser left hemisphere bias in the panic disorder group.     

Increased cortisol and decreased right ear advantage (REA) in dichotic listening following a negative mood induction

This study aimed to evaluate neuroendocrine responses and changes in perceptual asymmetry following an induced negative affect. Cortisol increasing in response to negative affect has been reported, while current brain models of emotion processing link negative affect to the right hemisphere. In this study, the Velten Mood Induction Procedure was used to generate neutral or negative affect in 44 healthy subjects. The PANAS scales were used to assess self-reported mood. A consonant-vowel dichotic listening (DL) test was applied after the neutral and negative affect inductions, and levels of salivary cortisol were determined by radioimmunoassay. For the negative affect condition, and congruent with the hypothesis tested, PANAS positive scores diminished (p<0.001) and PANAS negative scores increased (p<0.001), yielding an inverse correlation between them. A significant increase in cortisol levels was also seen (p<0.04). When taking cortisol reactivity into account, PANAS negative scores were higher for high-than for low-cortisol responders (p<0.02). Regarding DL, an increase in left ear items (p<0.04) and a decrease in right ear items (p<0.03) reported for those subjects who obtained a right ear advantage in the neutral condition. An explanation in terms of Kinsbourne's model for attentional-activation influences on DL is postulated and implications for the issue of affective illness are also discussed.     

Dichotic listening indices of right hemisphere semantic processing

A new dichotic listening technique, based on a psychophysical threshold procedure and providing ordinal scale measurement of lateral asymmetry, was used to investigate variation in the size of right-ear advantage for verbal vs manual response modalities across three semantic categories of stimuli in 60 right-handed males. For manual responders, abstract words elicited a significantly greater right-ear advantage than did concrete words, while emotional words elicited a non-significant left-ear advantage. Verbal responders showed no significant difference in the size of right-ear advantage across stimuli. The results suggest that both response modality and stimulus type are important variables for dichotic listening paradigms seeking evidence of right hemisphere contributions to semantic processing.