Increased corpus callosum size in musicians

The neural networks of music

Recent neuropsychological, transcranial Doppler sonographic, positron emission tomographic and functional nuclear magnetic resonance studies have indicated that musical perception is not dependent on the right hemisphere but on neural networks corresponding to the fundamental components of music in both hemispheres. In the brain there is no centre for music. Musicians have cerebral characteristics, anatomical as well as functional, which are correlated with the age at which they began their musical studies. This argues for cortical reorganization as a result of musical training. Whether these characteristics are to be ascribed to cortical plasticity alone, or to an innate structural property, or to both, remains an open question, however. Investigation of chromosomal defects, biochemical abnormalities and morphological features of congenital and degenerative brain diseases can provide further insight into the cerebral substrate of musicality.

Assessment of fine motor skill in musicians and nonmusicians: differences in timing versus sequence accuracy in a bimanual fingering task

While professional musicians are generally considered to possess better control of finger movements than nonmusicians, relatively few reports have experimentally addressed the nature of this discrepancy in fine motor skills. For example, it is unknown whether musicians perform with greater skill than control subjects in all aspects of different types of fine motor activities. More specifically, it is not known whether musicians perform better than control subjects on a fine motor task that is similar, but not identical, to the playing of their primary instrument. The purpose of this study was to examine the accuracy of finger placement and accuracy of timing in professional musicians and nonmusicians using a simple, rhythmical, bilateral fingering pattern and the technology that allowed separate assessment of these two parameters. Professional musicians (other than pianists) and nonmusicians were given identical, detailed and explicit instructions but not allowed physically to practice the finger pattern. After verbally repeating the correct pattern for the investigator, subjects performed the task on an electric keyboard with both hands simultaneously. Each subject's performance was then converted to a numerical score. While musicians clearly demonstrated better accuracy in timing, no significant difference was found between the groups in their finger placement scores. These findings were not correlated with subjects' age, sex, limb dominance, or primary instrument (for the professional musicians). This study indicates that professional musicians perform better in timing accuracy but not spatial accuracy while executing a simple, novel, bimanual motor sequence.

Morphology of Heschl's gyrus reflects enhanced activation in the auditory cortex of musicians

Using magnetoencephalography (MEG), we compared the processing of sinusoidal tones in the auditory cortex of 12 non-musicians, 12 professional musicians and 13 amateur musicians. We found neurophysiological and anatomical differences between groups. In professional musicians as compared to non-musicians, the activity evoked in primary auditory cortex 19-30 ms after stimulus onset was 102% larger, and the gray matter volume of the anteromedial portion of Heschl's gyrus was 130% larger. Both quantities were highly correlated with musical aptitude, as measured by psychometric evaluation. These results indicate that both the morphology and neurophysiology of Heschl's gyrus have an essential impact on musical aptitude.

Bimanual coordination and interhemispheric interaction

Bimanual coordination of skilled finger movements requires intense functional coupling of the motor areas of both cerebral hemispheres. This coupling can be measured non-invasively in humans with task-related coherence analysis of multi-channel surface electroencephalography. Since bimanual coordination is a high-level capability that virtually always requires training, this review is focused on changes of interhemispheric coupling associated with different stages of bimanual learning. Evidence is provided that the interaction between hemispheres is of particular importance in the early phase of command integration during acquisition of a novel bimanual task. It is proposed that the dynamic changes in interhemispheric interaction reflect the establishment of efficient bimanual 'motor routines'. The effects of callosal damage on bimanual coordination and learning are reviewed as well as functional imaging studies related to bimanual movement. There is evidence for an extended cortical network involved in bimanual motor activities which comprises the bilateral primary sensorimotor cortex (SM1), supplementary motor area, cingulate motor area, dorsal premotor cortex and posterior parietal cortex. Current concepts about the functions of these structures in bimanual motor behavior are reviewed.

The musician's brain as a model of neuroplasticity

Studies of experience-driven neuroplasticity at the behavioural, ensemble, cellular and molecular levels have shown that the structure and significance of the eliciting stimulus can determine the neural changes that result. Studying such effects in humans is difficult, but professional musicians represent an ideal model in which to investigate plastic changes in the human brain. There are two advantages to studying plasticity in musicians: the complexity of the eliciting stimulus music and the extent of their exposure to this stimulus. Here, we focus on the functional and anatomical differences that have been detected in musicians by modern neuroimaging methods.

Callosal contribution to procedural learning in children

A previous study in acallosal patients (De Guise, et al., 1999) has demonstrated the crucial role of the corpus callosum (CC) in a procedural learning task that requires the participation of both hemispheres. Because children often display limitations in interhemispheric communication linked to callosal immaturity, we expected that they would have difficulties learning a procedural skill that involved interhemispheric integration during its acquisition, but not when the skill was learned intrahemispherically. To test this hypothesis, 40 children, divided into 4 age groups (6 to 8 years, 9 to 11 years, 12 to 14 years, and 15 to 16 years), performed a modified version of the serial reaction time task developed by Nissen and Bullemer (1987). This task involves uni- or bimanual key-pressing responses to a fixed sequence of 10 visual stimuli that are repeated 80 times. All the children were able to learn the visuomotor skill in the unimanual condition and to transfer it interhemispherically. However, only the older children (12 years and over) learned the task in the bimanual (interhemispheric) condition. The results indicate that the maturation of the CC affects interhemispheric acquisition of a procedural skill in two different ways: While the immature CC appears to be sufficient to transfer a skill acquired by one hemisphere, a mature CC seems to be required to learn the skill bihemispherically. The latter skill was achieved around the age of 12, coinciding with the end of the maturation cycle of the CC. Although the young children were unable to learn the bimanual task implicitly, some of them showed explicit knowledge of the procedure, confirming once again the dissociation between explicit and implicit memory suggested by Squire (1992).

Effects of musical training on speech-induced modulation in corticospinal excitability

We investigated the effect of previous musical training on lateralization of language as indexed by the effects of reading aloud on the modulation of motor evoked potentials (MEPs) induced in the first dorsal interosseus muscles (FDI) by transcranial magnetic stimulation (TMS) of the primary motor cortex. We studied 13 right-handed subjects, seven musicians who had been playing a musical instrument for >10 years and six controls who had never studied a musical instrument. In all subjects, the amplitude of MEPs in the right FDI was facilitated by reading aloud. However, the musicians also showed significant facilitation in the left FDI, while controls did not. These results illustrate striking effects of musical training on lateralization of motor and language functions.

Differences in white matter architecture between musicians and non-musicians: a diffusion tensor imaging study

Previous studies found structural brain differences between musicians and non-musicians. In order to determine possible differences in white matter architecture, diffusion tensor imaging was performed on five adult subjects with musical training since early childhood, and seven adult controls. The musicians displayed significantly greater fractional anisotropy (FA) in the genu of the corpus callosum, while significantly less FA was found in the corona radiata and the internal capsule bilaterally. Further areas also showed significant differences. We hypothesize that these changes are due to the cognitive and motor effects, respectively, of musical training.

The size of corpus callosum and functional connectivities of cortical regions in finger and shoulder movements

The correlations between the size of corpus callosum and the inter- and intra-hemispheric EEG coherence and the spatial EEG synchronization during finger and shoulder movements were analyzed in nine right-handed men. The cross-sectional surface areas of corpus callosum (CC) and of seven callosal regions were measured from the mid-sagittal slice of the anatomical MRI. Movement-related coherence between pairs of EEG electrodes overlying the central and parietal regions of both hemispheres was computed after spatially filtering EEG data by the Laplacian operator method. The spatial EEG synchronization was evaluated using omega-complexity, a novel measure which quantifies the number of independent sources of spontaneous EEG oscillations. The amplitude of coherence between the left and right S1/M1 areas after movement onset in the lower alpha band (7.8-9.8 Hz) correlated with the size of the callosal body in both types of movement. The size of the callosal body also correlated with the C3-Cz coherence in the 15.6-19.5 Hz band in finger movement, and in the 15.6-23.5 Hz band in shoulder movements. The size of the rostral, anterior intermediate and posterior intermediate truncus of CC correlated with omega-complexity in both types of movements indicating more foci of synchronized EEG oscillations in subjects with a large callosal truncus. The results suggest that the size of callosal truncus which is known to connect the primary sensorimotor and the supplementary motor areas of both hemispheres contributes to the coupling of EEG oscillations during voluntary finger and shoulder movements.

Absolute pitch and planum temporale

An increased leftward asymmetry of the planum temporale (PT) in absolute-pitch (AP) musicians has been previously reported, with speculation that early exposure to music influences the degree of PT asymmetry. To test this hypothesis and to determine whether a larger left PT or a smaller right PT actually accounts for the increased overall PT asymmetry in AP musicians, anatomical magnetic resonance images were taken from a right-handed group of 27 AP musicians, 27 nonmusicians, and 22 non-AP musicians. A significantly greater leftward PT asymmetry and a significantly smaller right absolute PT size for the AP musicians compared to the two control groups was found, while the left PT was only marginally larger in the AP group. The absolute size of the right PT and not the left PT was a better predictor of music group membership, possibly indicating "pruning" of the right PT rather than expansion of the left underlying the increased PT asymmetry in AP musicians. Although early exposure to music may be a prerequisite for acquiring AP, the increased PT asymmetry in AP musicians may be determined in utero, implicating possible genetic influences on PT asymmetry. This may explain why the increased PT asymmetry of AP musicians was not seen in the group of early beginning non-AP musicians.

Rhythm and melody in children and adolescents after left or right temporal lobectomy

Rhythm (a pattern of onset times and duration of sounds) and melody (a pattern of sound pitches) were studied in 22 children and adolescents several years after temporal lobectomy for intractable epilepsy. Left and right lobectomy groups discriminated rhythms equally well, but the right lobectomy group was poorer at discriminating melodies. Children and adolescents with right lobectomy, but not those with left temporal lobectomy, had higher melody scores with increasing age. Rhythm but not melody was related to memory for the right lobectomy group. In neither group was melody related to age at onset of non-febrile seizures, time from surgery to music tests, or the linear amount of temporal lobe resection. Pitch and melodic contour show different patterns of lateralization after temporal lobectomy in childhood or adolescence.

Music and nonmusical abilities

Reports that exposure to music causes benefits in nonmusical domains have received widespread attention in the mainstream media. Such reports have also influenced public policy. The so-called "Mozart effect" actually refers to two relatively distinct phenomena. One concerns short-term increases in spatial abilities that are said to occur from listening to music composed by Mozart. The other refers to the possibility that formal training in music yields nonmusical benefits. A review of the relevant findings indicates that the short-term effect is small and unreliable. Moreover, when it is evident, it can be explained by between-condition differences in the listener's mood or levels of cognitive arousal. By contrast, the effect of music lessons on nonmusical aspects of cognitive development is still an open question. Several studies have reported positive associations between formal music lessons and abilities in nonmusical (e.g., linguistic, mathematical, and spatial) domains. Nonetheless, compelling evidence for a causal link remains elusive.

Timbre-specific enhancement of auditory cortical representations in musicians

Neural imaging studies have shown that the brains of skilled musicians respond differently to musical stimuli than do the brains of non-musicians, particularly for musicians who commenced practice at an early age. Whether brain attributes related to musical skill are attributable to musical practice or are hereditary traits that influence the decision to train musically is a subject of controversy, owing to its pedagogic implications. Here we report that auditory cortical representations measured neuromagnetically for tones of different timbre (violin and trumpet) are enhanced compared to sine tones in violinists and trumpeters, preferentially for timbres of the instrument of training. Timbre specificity is predicted by a principle of use-dependent plasticity and imposes new requirements on nativistic accounts of brain attributes associated with musical skill.

Hemispheric and gender-related differences in the gross morphology of the anterior cingulate/paracingulate cortex in normal volunteers: an MRI morphometric study

The sulci and gyri found within the anterior cingulate (AC), and across the cerebrum generally, have been found to vary in location and complexity from one individual to the next, making it difficult to analyze imaging data accurately and systematically. In this study, we examined the nature of morphometric variance in the AC of the left and right cerebral hemispheres using high-resolution structural magnetic resonance imaging (MRI) acquired from 176 healthy volunteers. Depending on the presence of a paracingulate sulcus (PCS) and its antero-posterior extent, three types of AC patterns were identified: 'prominent', 'present' and 'absent'. Hemispheric comparisons across the whole sample showed the PCS to be more commonly 'prominent' in the left hemisphere and more commonly 'absent' in the right hemisphere. There was a significant gender difference, such that males showed an asymmetric pattern characterized by increased fissurization of the left AC, while females showed greater symmetry, with less fissurization of the left AC. Overall cerebral morphology, namely hemispheric volume and hemispheric fissurization, were also measured and used as independent variables as well as covariates in the analyses in order to ascertain the specificity of the results regarding AC morphology. Results showed that cerebral volume for males was larger on the right than on the left while fissurization showed the reverse asymmetry of greater leftward fissurization. In contrast, females were symmetric in both respects. The findings regarding AC morphology could not be explained by differences in these overall cerebral measures or by differences in age and handedness within the population. The results suggest that in the normal male brain, there exist morphological asymmetries at both the global and local levels that are less apparent in the female brain. The findings have implications for future studies examining the organization, development and functional anatomy of the AC.

Comparative and correlative neuroanatomy for the toxicologic pathologist

Xenobiotic-induced neuroanatomic alterations are always regarded as adverse and are commonly used to define reference doses to manage neurotoxic risk. Thus, the neuropathologist plays an essential role in evaluating potential neurotoxicants. The pathologist must be able to recognize the morphologic differences that exist among species, strains, and ages or between genders (comparative neuroanatomy) and to grasp the impact of structural damage on neural function (correlative neuroanatomy). Brain anatomy and function may be used to group the mammals used in neurotoxicity bioassays into 3 classes: rodent, carnivore, and primate. Neural function may or may not be affected by the structural divergence. Rodents are preferred for neurotoxicity assays because their reduced body size allows optimal perfusion at little cost and their smaller brain size permits screening of multiple regions using few sections. However, care must be exercised when interpreting rodent neuropathology data because the rodent paleocortex does not recapitulate the sophisticated neocortical circuitry and functions of carnivores and primates. Knowledge of the neuroanatomic variations that exist among test species assists the neuropathologist in defining the relevance of structural alterations, the potential clinical sequelae of such findings, and the possible significance of similar changes in humans.

Influence of learning to read and write on the morphology of the corpus callosum

Variations in the individual anatomy of the corpus callosum have been reported in several conditions. There seem to be genetic influencing factors, but it is impossible to rule out some environmental ones. This study focuses on the question of the environmental factors, using formal learning to read and write as the main difference in the groups to be compared. Based on magnetic resonance imaging sagital images, the contour of the corpus callosum (CC) of 41 carefully selected women (18 illiterate and 23 literate) was digitized. The comparison between the two groups showed a small difference in the region of the CC where parietal fibres are thought to cross. This region is thinner in illiterate subjects. As illiteracy in this group is the result of social constraints, and the two groups that were compared are well matched for other cultural and pragmatic aspects than literacy, the results are interpreted as showing the possible influence of formal learning to read and write, on the biological development of the brain.

Abnormal callosal morphology in male adult dyslexics: relationships to handedness and phonological abilities

The classical notion that developmental dyslexia may somehow relate to impaired communication between hemispheres has not yet received convincing support. Sixteen dyslexic adults and 12 controls received a high resolution brain MRI scan for morphometric study of the corpus callosum. Automatized measurements of callosal area and calculation of indices defining the general morphology of the callosal mid-surface were performed. Each participant received global intelligence and reading achievement evaluation; dyslexics were further proposed specific neuropsychological tests specially designed to explore the mechanisms of reading impairment. It just appears from the group comparisons (1) that the dyslexics' corpus callosum displays a more circular and evenly thicker general shape, and (2) that the midsagittal surface is on the average larger than in controls, in particular in the isthmus. Moreover, the different morphometric characteristics of the dyslexic brain correlated with the degree of impairment on various tests exploring phonological abilities. In vivo morphometry of the corpus callosum may provide valuable hints for understanding developmental learning disorders and their consequences in adults.

The relation of planum temporale asymmetry and morphology of the corpus callosum to handedness, gender, and dyslexia: a review of the evidence

Asymmetry of the planum temporale in relation to handedness, gender, and dyslexia is reviewed. The frequency of rightward asymmetry is rather higher than are estimates of the proportion of right hemisphere speech representation in the general population. Conversely, the frequency of leftward asymmetry is lower than the proportion of the population with left hemisphere speech. Neuro-anatomic asymmetry may relate more to handedness than to language lateralization. There are suggestions that neuroanatomic asymmetry is reduced in females compared to males but the data are inconclusive. Reports concerning handedness and gender differences in callosal structure are conflicting but, as with planum asymmetry, any effect of handedness is as likely to relate to degree as to direction of handedness. It has been reported that the plana are more often symmetrical in size or larger on the right side among dyslexics than controls but this has not always been found. However, greater frequency of atypical (a)symmetry of the planum in dyslexia would be consistent with the absence of a factor which, when present, biases the distribution of planum asymmetry toward the left (and handedness towards the right) as hypothesized by Annett (1985). Studies of the size of the corpus callosum in dyslexia have produced conflicting findings.

Hand skill asymmetry in professional musicians

Hand skill asymmetry on two handedness tasks was examined in consistent right-handed musicians and nonmusicians as well as mixed-handed and consistent left-handed nonmusicians. Musicians, although demonstrating right-hand superiority, revealed a lesser degree of hand skill asymmetry than consistent right-handed nonmusicians. Increased left-hand skill in musicians accounted for their reduced asymmetry. Musicians predominantly playing keyboard instruments demonstrated superior tapping performance than musicians playing predominantly string instruments, although they did not differ with respect to hand skill asymmetry. Since the diminished tapping asymmetry in musicians was related to early commencement but not duration of musical training, results are interpreted as an adaptation process due to performance requirements interacting with cerebral maturation during childhood.