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An important feature of perception is plasticity, enabling the acquisition of new perceptual representations to facilitate responding to regular stimuli in the environment. The auditory system has shown capacity for plasticity into adulthood, allowing the perceptual discrimination abilities to be improved by training. It has been suggested that a certain form of passive learning using rapid sensory stimulation can lead to plasticity in the sensory cortex through mechanisms similar to long-term potentiation. Here we demonstrate using electroencephalography that brief rapid auditory stimulation (2 min, 13 Hz) with a sinusoidal tone (1025 Hz) led to increased discriminability of the stimulated tone from a standard tone (1000 Hz) as indexed by mismatch negativity event-related potential. This shows that perceptual learning with brief exposure can cause plastic changes similar to long-term training., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Morphometric neuroimaging studies on healthy adult individuals regularly report a positive association between intelligence test performance (IQ) and structural properties of the corpus callosum (CC). At the same time, studies examining the effect of callosotomy on epilepsy patients report only negligible changes in IQ as result of the surgery, partially contradicting the findings of the morphometry studies. Objective of the present meta-analysis of individual participant data (IPD) of 87 cases from 16 reports was to re-investigate the effect of callosotomy on full scale IQ as well as on the verbal and performance subscale under special consideration of two possible moderating factors: pre-surgical IQ levels and the extent of the surgery (complete vs. anterior transsection). The main finding was that callosotomy selectively affects performance IQ, whereby the effect is modulated by the pre-surgical level of performance. Patients with an above-median pre-surgery performance IQ level show a significant average decrease of -5.44 (CI 95% : - 8.33 to - 2.56) IQ points following the surgery, while the below-median group does not reveal a significant change in IQ (mean change: 1.01 IQ points; CI 95% : -1.83 to 3.86). Thus, the present analyses support the notion that callosotomy has a negative effect on the patients' performance IQ, but only in those patients, who at least have an average performance levels before the surgery. This observation also lends support to the findings of previous morphometry studies, indicating that the frequently observed CC-IQ correlation might indeed reflect a functional contribution of callosal interhemispheric connectivity to intelligence-test performance., (Copyright © 2017 The Author(s). Published by Elsevier B.V. All rights reserved.)

Structural asymmetries in white matter tracts within the language system have been suggested to be one of the factors underlying functional language lateralization. To test this assumption, the present study examined how performance in the dichotic listening task, a behavioral measure of language dominance, is affected by macro- and microstructural properties of the arcuate and uncinate fasciculus. To this end, whole brain tractography was performed on 29 diffusion tensor imaging datasets obtained from healthy adult participants. Mean tract volume and fractional anisotropy of the uncinate and arcuate fasciculus were linked to the individual extent of the right ear advantage in the dichotic listening task. On the macrostructural level, both arcuate and uncinate fasciculus had a larger tract volume in the left compared to the right hemisphere. In contrast, fractional anisotropy was higher in the right than in the left arcuate fasciculus. These structural asymmetries were linked to functional lateralization, that is, tract volume and fractional anisotropy of the left arcuate fasciculus were positively correlated to the strength of functional language lateralization, as was the volume of the right uncinate fasciculus. In conclusion, the results of the present study suggest that both micro- and macro-structural properties of language-relevant intrahemispheric white matter tracts modulate the behavioral correlates of language lateralization., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

The dichotic listening test is non-invasive behavioural technique to study brain lateralization and it has been shown, that its results can be systematically modulated by varying stimulation properties (bottom-up effects) or attentional instructions (top-down effects) of the testing procedure. The goal of the present study was to further investigate the bottom-up modulation, by examining the effect of differences in the right or left ear stimulus intensity on the ear advantage. For this purpose, interaural intensity difference were gradually varied in steps of 3 dB from -21 dB in favour of the left ear to +21 dB in favour of the right ear, also including a no difference baseline condition. Thirty-three right-handed adult participants with normal hearing acuity were tested. The dichotic listening paradigm was based on consonant-vowel stimuli pairs. Only pairs with the same voicing (voice or non-voiced) of the consonant sound were used. The results showed: (a) a significant right ear advantage (REA) for interaural intensity differences from 21 to -3 dB, (b) no ear advantage (NEA) for the -6 dB difference, and (c) a significant left ear advantage (LEA) for differences form -9 to -21 dB. It is concluded that the right ear advantage in dichotic listening to CV syllables withstands an interaural intensity difference of -9 dB before yielding to a significant left ear advantage. This finding could have implications for theories of auditory laterality and hemispheric asymmetry for phonological processing.

The present study examined how interhemispheric transfer time (IHTT) is affected by interindividual differences in corpus callosum (CC) architecture. For this purpose the CC of 42 healthy male subjects was assessed by applying a combination of morphological and diffusion-tensor magnetic resonance imaging to characterize the CC on macro- (midsagittal area) and microstructural level (mean diffusion, fractional anisotropy). Following the so-called Poffenberger paradigm, IHTT was determined with both reaction time measures and event-related potentials recorded in response to stimuli briefly presented to either left or right visual hemifield. Statistical analysis revealed significant negative correlations between mean diffusion and IHTT estimates derived from the P100 component (at O1/O2 electrode pair), particularly in the posterior CC subregion. Interpreting mean diffusion as an index of microstructural tissue properties, IHTT appears to be directly related to the structural integrity of the posterior CC.