Functional Cerebral Asymmetries Research Articles

Gender-Specific Functional Cerebral Asymmetries and Unilateral Cerebral Lesion Sequelae

The magnitude and direction of cerebral lateralization are thought to be sexually dimorphic. Numerous human studies indicate gender-specific differences in functional cerebral asymmetries (FCAs) for various functions. Females are thought to have a decreased magnitude of inter-hemispheric cortical lateralization compared with males, whereas males exhibit a greater degree of cortical asymmetry than females for components of cognitive and perceptual processing. Also, a large body of evidence has shown that FCAs fluctuate across the menstrual cycle, presumably as a result of cycle-related hormonal changes. Awareness of gender-based differences of the human brain may enable better understanding of differences in functional outcome between men and women after unilateral cerebral lesion.

Hand preference for spontaneously unimanual and bimanual coordinated tasks in wild Sichuan snub-nosed monkeys: Implication for hemispheric specialization

Lateralized behaviour has been studied as an observable measure of cerebral functional asymmetry for many years, and interest in the evolutionary origins of lateralized behaviour in humans has prompted research into the study of manual laterality in nonhuman primates. The Sichuan snub-nosed monkey (Rhinopithecus roxellana) is a rarely studied species as far as laterality research is concerned. In this study, we investigated hand preference in spontaneously unimanual and bimanual coordinated tasks during grooming in wild R. roxellana in the Qinling Mountains of China. We chose 26 adult individuals (20 females and 6 males) for both tasks. Wild R. roxellana shows group-level left-handedness in bimanual coordinated grooming task, but not in unimanual grooming task, which is just found on the individual-level based on z-scores. Both the direction and strength of hand preference in the bimanual task are significantly stronger than that in unimanual task. Our findings present the first evidence of group-level handedness in wild monkeys although group-level handedness had been reported in wild apes [e.g. Pongo pygmaeus: Rogers LJ, Kaplan G. Hand preference and other lateral biases in rehabilitated orangutans, Pongo pygmaeus pygmaeus. Anim Behav 1996;51:13–25]. The results in R. roxellana support the theory of task complexity as well as the postural origin hypothesis.

Translation as a Psycholinguistic Phenomenon

The article sketches the outlines of a theoretical framework for the analysis of translation of literary texts, viewed as psycho-semiotic phenomenon and based on evaluation of earlier attempts in this direction, and on the results of a psycholinguistic empirical study of translations. Central to this framework is the recent insight that the human cerebral hemisphere functional asymmetry somehow plays a role in structuring the fictional text by its author and in its processing by the interpreter. It is argued that the texts of modernism and post-modernism contain information blocks describing a character's perception of events in altered states of consciousness. This model helps to explain how a translator's inappropriate linguistic choice may influence the target language reader's aesthetic reaction.

Music and the Debate on Cerebral Dominance: The Classic Work of Bever and Chiarello

Music and the Debate on Cerebral Dominance: The Classic Work of Bever and Chiarello

Visual asymmetries in Japanese quail (Coturnix japonica) retain a lifelong potential for plasticity.

Adult Japanese quail display left-eye/right-hemisphere dominance in visually guided sexual tracking. In 2 experiments, the authors set out to answer if this functional cerebral asymmetry is modifiable by posthatch monocular deprivation. In Experiment 1, the left or the right eye of 2-day old quail were closed for 70 days. Quail were run in a left- or a right-turning runway to obtain access to a conspecific of the opposite sex. The performance of both left and right eye systems was equal. In Experiment 2, the deprived eyes of the quail were opened and the previously open eyes were closed. They were tested with the same runways. Overall, running speed was very low, but the quail showed a left-eye/right-hemisphere superiority. Altogether, these experiments evince 3 insights into cerebral asymmetries in quail. First, posthatch asymmetries of visual input can alter lateralized behavior to an important extent. Second, cerebral asymmetries could involve an interhemispheric inhibition that can be modified by epigenetic factors. Third, even long-term visual deprivation does not abolish a previously established cerebral asymmetry.

Estradiol Modulates Functional Brain Organization during the Menstrual Cycle: An Analysis of Interhemispheric Inhibition

According to the hypothesis of progesterone-mediated interhemispheric decoupling (Hausmann and Güntürkün, 2000), functional cerebral asymmetries (FCAs), which are stable in men and change during the menstrual cycle in women, are generated by interhemispheric inhibition of the dominant on the nondominant hemisphere. The change of lateralization during the menstrual cycle in women might indicate that sex hormones play an important role in modulating FCAs. We used functional magnetic resonance imaging to examine the role of estradiol in determining cyclic changes of interhemispheric inhibition. Women performed a word-matching task, while they were scanned twice during the cycle, once during the menstrual and once during the follicular phase. By use of a connectivity analysis we found that the inhibitory influence of left-hemispheric language areas on homotopic areas of the right hemisphere is strongest during the menses, resulting in a pronounced lateralization. During the follicular phase, due to rising estradiol levels, inhibition and thus functional cerebral asymmetries are reduced. These results reveal a powerful neuromodulatory action of estradiol on the dynamics of functional brain organization in the female brain. They may further contribute to the ongoing discussion of sex differences in brain function in that they help explain the dynamic part of functional brain organization in which the female differs from the male brain.

Estrogen therapy affects right hemisphere functioning in postmenopausal women

It has been suggested that hormone therapy (HT) in postmenopausal women differentially affects verbal and visuo-spatial abilities which mainly rely on left hemisphere (LH) and right hemisphere (RH) functioning, respectively. Thus, it seems likely that HT-related effects on cognition are driven by associated hormonal changes and their impact on functional brain organization, and functional cerebral asymmetries (FCAs) in particular. The present study investigated HT-related effects on FCAs in sixty-seven postmenopausal women who received hormone therapy either with estrogen (E) alone ( n = 14), an E-gestagen combination ( n = 22) or without HT (control group, n = 31). Saliva levels of free E and progesterone (P) were analyzed using chemiluminescence assays. FCAs were measured with the visual half-field (VHF) technique using a word matching and a figural comparison task. In agreement with previous results, a postmenopausal control group showed a left hemisphere (LH) advantage in the verbal task and a right hemisphere (RH) advantage in visuo-spatial processing. In contrast, both HT groups revealed significantly reduced FCAs in the figural comparison task as a result of an E-related decrease in RH performance. The findings suggest that E-therapy in postmenopausal women can affect visuo-spatial abilities by modulating the functional brain organization and RH functioning in particular.

Hemispheric Specialization in Dogs for Processing Different Acoustic Stimuli

Considerable experimental evidence shows that functional cerebral asymmetries are widespread in animals. Activity of the right cerebral hemisphere has been associated with responses to novel stimuli and the expression of intense emotions, such as aggression, escape behaviour and fear. The left hemisphere uses learned patterns and responds to familiar stimuli. Although such lateralization has been studied mainly for visual responses, there is evidence in primates that auditory perception is lateralized and that vocal communication depends on differential processing by the hemispheres. The aim of the present work was to investigate whether dogs use different hemispheres to process different acoustic stimuli by presenting them with playbacks of a thunderstorm and their species-typical vocalizations. The results revealed that dogs usually process their species-typical vocalizations using the left hemisphere and the thunderstorm sounds using the right hemisphere. Nevertheless, conspecific vocalizations are not always processed by the left hemisphere, since the right hemisphere is used for processing vocalizations when they elicit intense emotion, including fear. These findings suggest that the specialisation of the left hemisphere for intraspecific communication is more ancient that previously thought, and so is specialisation of the right hemisphere for intense emotions.

The right hemisphere fails to orient to the negative valence of visually presented words

To assess cerebral functional asymmetry for accessing the meaning of emotional words, native English speakers were asked to make lexical decisions to emotional words, neutral words and nonwords briefly flashed in their left or right visual field, that is, perceived by their right or left visual cortex, respectively. Emotionally negative words had an overall probability of occurrence of 12.5% in each visual field and were expected to elicit a P3b event-related potential modulation indexing shifts of attention. Emotionally negative words elicited a P3b when perceived by the left visual cortex but failed to trigger such attention-related response when perceived by the right hemisphere. The results suggest relative insensitivity on the part of the right hemisphere in registering the negative emotional valence of written words.

The influence of sex hormones on functional cerebral asymmetries in postmenopausal women

Studies investigating changes in functional cerebral asymmetries (FCAs) with hormonal fluctuations during the menstrual cycle in young women have led to controversial hypotheses about an influence of estrogen (E) and/or progesterone (P) on FCAs. Based on methodical, but also on principal problems in deriving conclusions about hormone effects from correlational designs, the present study investigated hemispheric asymmetries in postmenopausal women, who received hormone replacement either with E alone (E group, n = 32), an E–P combination (E–P group, n = 29) or no hormone substitution (control group, n = 31). Speed and accuracy of responses to a word- and a face decision task, both presented laterally by means of the visual half field technique, were assessed. The control group showed the typical pattern of hemispheric asymmetry with more correct responses to verbal stimuli presented in the right visual field (RVF) and to face stimuli presented in the left visual field (LVF). A hormone-effect was demonstrable only for the verbal task, in which the E group showed an enhanced performance of the right hemisphere (LVF). The E–P group showed no significant differences to the control group or the E group. The results suggest a role of E in the modulation of FCAs at least with regard to verbal processing.

The evolutionary origins of functional cerebral asymmetries in humans: Does lateralization enhance parallel processing?

Functional cerebral asymmetries (FCAs) are a fundamental principle of brain organization in many species. However, little is known about why they have evolved. Since FCAs are such a widespread phenomenon they seem to constitute an evolutionary selective advantage. According to a prominent hypothesis, an asymmetric brain should be associated with advantages in parallel processing, i.e. doing two tasks simultaneously. The strong version of this hypothesis implies that lateralized, instantaneous and complementary tasks are performed more efficiently with a highly lateralized brain. Using a visual half-field procedure, we wanted to test this strong version of the parallel-processing hypothesis in humans. Thirty-two participants (17 women, 15 men) were investigated. First, we assessed the degree of lateralization in a face/non-face and a word/non-word discrimination task favouring the right and left hemisphere, respectively. Based on a median split, subjects were divided into a rather symmetric and a rather asymmetric group. Then, all participants completed both tasks simultaneously. The results revealed that the rather symmetrically organized participants outperformed asymmetric participants in accuracy and response times. Hence, the strong version of the parallel-processing hypothesis has to be revised.

A Comparative Analysis of Functional Cerebral Asymmetry in Lesbian Women, Heterosexual Women, and Heterosexual Men

This study tested dichotic listening performance, a measure of functional cerebral asymmetry previously shown to be sexually dimorphic, in homosexual women (n=23), heterosexual women (n=27), and heterosexual men (n=24). All participants completed a verbal consonant-vowel dichotic listening task. On three laterality indices, heterosexual men displayed a significantly greater right-ear advantage compared to heterosexual women only. Homosexual women did not differ significantly from heterosexual men or from heterosexual women. Post-hoc comparisons (with a statistical correction) for each ear separately showed that heterosexual men displayed significantly greater right-ear scores compared to heterosexual women only. These data suggest that lesbian women are somewhat masculinized in their functional cerebral asymmetry. The results were interpreted in the context of sexual variation in models of linguistic hemispheric processing.

Functional cerebral asymmetry in auditory motion perception

Several studies have shown a right-hemispheric advantage for sound localisation. However, most of these studies used stationary sound stimuli, although in most everyday situations humans are in motion when localising sound, or face a moving sound source. To elucidate the question of a functional asymmetry in cortical processing of auditory motion information, we tested 23 neurologically healthy human participants. Virtual leftward or rightward motion (broadband noise) was presented with variable movement angles (MA) in the horizontal plane (via headphones) in either the participants’ left or right hemispace. Participants had to indicate whether the sound moved left or rightward. The frequency of “right” judgements determined as a function of MA had a sigmoidal shape in both hemispaces, indicating significant overall discrimination of motion direction. However, the frequency of correct judgements revealed a significantly better performance for the left than for the right hemispace, suggesting a superiority of the right hemisphere. This finding is in agreement with recent neuroimaging results showing higher right-hemispheric activity during localisation of moving sounds. The results might also point to a supramodal right-hemisphere advantage in the attentional processing of motion perception.

Sex hormonal modulation of hemispheric asymmetries in the attentional blink

The present study examines differences in functional cerebral asymmetries modulated by gonadal steroid hormones during the menstrual cycle in women. Twenty-one right-handed women with regular menstrual cycles performed a double-stream rapid serial visual presentation (RSVP) task, with one stream in each visual field, during the low steroid menses and the high steroid midluteal phase. They were required to detect a target item, and then a probe item, each of which could appear in either stream. If the probe item appeared 200 ms after the target, detection of the probe was impaired-a phenomenon known as the "attentional blink." This occurred in both streams in the midluteal phase, but only in the right visual field during menses. Thus low steroid levels appeared to restrict the attentional blink to the left hemisphere, while high levels of estradiol and progesterone in the midluteal phase appeared to reduce functional asymmetries by selectively increasing the attentional blink in the right hemisphere. This effect appears to be mediated by estradiol rather than progesterone, and it is compatible with the assumption of a hormone-related suppression of right hemisphere functions during the midluteal phase.

Hemispheric asymmetry in spatial attention across the menstrual cycle

Functional cerebral asymmetries (FCAs) are known to fluctuate across the menstrual cycle. The mechanisms of these sex hormonal modulations are poorly understood. It has been suggested that gonadal steroid hormones might suppress or specifically activate one hemisphere. However, recent studies suggest that high levels of gonadal steroid hormones reduce FCAs by its modulating effects on cortico-cortical transmission. To investigate the activating effects of gonadal steroid hormones on the interhemispheric interaction, a visual line-bisection task was administered to normally cycling women during menses and the midluteal cycle phase as well as to similar-aged healthy men. The results replicate previous findings of a sex difference in line-bisection as a function of hand-use and show that the hand-use effect fluctuates across the menstrual cycle. High levels of estradiol during the midluteal phase were related to a decrease of the hand-use effect. It is concluded that cycle-related fluctuations in levels of gonadal steroid hormones affect hemispheric asymmetry of spatial attention, presumably by interhemispheric spreading of neuronal activation.

Functional Brain Asymmetries During Visuomotor Tracking

This study examined brain asymmetries elicited during visuomotor tracking. Thirty-two healthy participants performed a fixed gaze, dynamic, pinch force, visuomotor tracking task during a functional magnetic resonance imaging study. The dynamic task required the subject to press a rubber bulb with the thumb to trace a cosine square wave varying in force amplitude from 0-500 cN and having a frequency of 1.5 Hz. Response hand order and direction of the stimulus presentation (right-to-left or left-to-right) were permuted across participants. Two forms of functional cerebral asymmetry were observed, hemispheric specialization and homologous lateralized response. The superior portion of the right middle frontal gyrus and the left supplementary motor area appeared specialized for VM tracking regardless of response hand used or stimulus movement direction. Lateralized effects appeared in the primary sensorimotor hand area, putamen, parietal operculum/posterior insula, dentate nucleus of the cerebellum, precuneus, and middle occipital gyrus. These lateralized areas of activation surfaced when either response hand or direction of stimulus movement was manipulated. The VM task used in this study activated asymmetrical neural activity in the vertically organized skelotomotor system and in sensory systems involving visual attention or proprioception.

Hemispheric asymmetry for linguistic prosody: A study of stress perception in Croatian

The aim of the study was to test for possible functional cerebral asymmetry in processing one segment of linguistic prosody, namely word stress, in Croatian. The test material consisted of eight tokens of the word pas under a falling accent, varying only in vowel duration between 119 and 185 ms, attached to the end of a frame sentence. The sentence could, depending on the duration of the vowel, mean ‘This is a beautiful dog’ or ‘This is a beautiful belt/waist.’ Each sentence was presented eight times in three dichotic listening conditions (binaural, left ear only, right ear only), in random order. Fourty healthy female right-handers participated in a forced-choice lexical task. For each presented sentence they had to decide whether it referred to the animal (short vowel in the key word) or to the belt/waist (long vowel in the key word). Their oral responses were analyzed in terms of response time and categoricity. No consistent significant differences were found among listening conditions. The responses possibly reflect the nonlateralized activity of subcortical regions or a simultaneous activity of both hemispheres relying on different cues.

Functional Cerebral Asymmetry and Its Possible Evolution in Historical Times

The paper addresses problems of the development of visual spatial functions of the right hemisphere of the human brain in ontogeny and phylogeny. The problem is being treated as an interdisciplinary one, and its potential as evidence of significant changes in cerebral asymmetry in historical times is discussed. Data from evolutionary physiology, anthropology, neuropsychology, and visual art history beginning with the Paleolithic are considered together. The authors pay special attention to such functions as perception of volume of objects and depth of three-dimensional visual scenery as well as perception of the face and emotional expressiveness both in clinical pathology and in normal subjects at different stages of ontogeny, and the appearance of these features in the history of art.

Functional cerebral asymmetry in hostility: A dual task approach with fluency and cardiovascular regulation

The influence of hostility levels on verbal and nonverbal fluency, and the concurrent cerebral regulation of autonomic nervous system functioning was examined in 48 right-handed males, half classified as low-hostile, and half as high-hostile. Recent research has supported inhibitory roles for the anterior right cerebrum in sympathetic regulation, and the anterior left cerebrum in parasympathetic regulation. Two neuropsychological tests purportedly mediated by left and right anterior cerebral systems, respectively, are the Controlled Oral Word Association Test and the Ruff Figural Fluency Test. Fluency and perseverative errors were assessed using these measures. Systolic and diastolic blood pressure, and heart rate were assessed with a digital blood pressure meter. It was predicted that high-hostile men would evidence interference on cardiovascular regulation concurrent with the nonverbal fluency task in comparison to low-hostile males. Further, interference was expected to manifest in the cognitive variable with more perseverative errors on the nonverbal fluency task in high-hostile males than in low-hostile males. The results support a capacity-limited prediction. High-hostile males evidenced significantly heightened systolic blood pressure during the nonverbal fluency task in comparison with low-hostile males. Further, high-hostile males displayed more perseverative errors in nonverbal fluency than did the low-hostile males. These results support the expectation that differences exist between high- and low-hostile males for right frontal functioning. These findings were discussed within the proposed anterior–posterior inhibition model of hostility.

INVESTIGATION OF THE LATERALITY OF HOSTILITY, CARDIOVASCULAR REGULATION, AND AUDITORY RECOGNITION

This experiment tested a hypothesis linking the right cerebral regulation of hostility and cardiovascular arousal. First, replication of previous research supporting heightened cardiovascular (systolic blood pressure [SBP] and diastolic blood pressure [DBP]) reactivity among high hostile participants was partially successful. Second, dynamic variations in functional cerebral asymmetry in response to emotional linguistic processing was measured. Thirty low- and high-hostile, undergraduate volunteer participants (n = 30) were identified using the Cook Medley Hostility Scale (CMHS). Only healthy, right-handed male participants completed the experiment. All participants completed the negative affective auditory verbal learning test (AAVLT). Cardiovascular measures (SBP and DBP) were recorded and dichotic listening procedures were administered before and after the cognitive affective stressor. The results support greater left cerebral activation among both groups following the dichotic phoneme listening tasks and greater right cerebral activation among both groups following an emotional linguistic (affective verbal learning) cognitive stressor.