Behavioural Brain Research 89 (1997) 243 – 258 Research report EEG coherence changes during finger tapping in acallosal and normal children: a study of inter- and intrahemispheric connectivity M. Knyazeva a , T. Koeda b , C. Njiokiktjien c, *, E.J. Jonkman c , M. Kurganskaya a , L. de Sonneville c , V. Vildavsky a a Research Institute of Deelopmental Physiology, Russian Academy of Education, 119121, Pogodinskaya 8 -2, Moscow, Russia b Diision of Child Neurology, Institute of Neurological Sciences, Tottori Uniersity Faculty of Medicine, Nishi -machi 86, Yonago 683, Japan c Pediatrics Policlinic, Reception L, Academic Hospital, P.O. Box 7057, NL-1007 MB Amsterdam, The Netherlands Received 8 August 1996; received in revised form 11 April 1997; accepted 11 April 1997 Abstract The EEG inter- and intrahemispheric coherences (ICoh and HCoh) in the ,  and  bands were studied in an acallosal group (ACCG) of five children and a normal group of 30 sex- and age-matched children (NG) during resting and tapping conditions. Being functionally deficient, tapping in the ACCG was characterized by increased intertap intervals and variability (in right-hand tapping) and by variability together with decreased synchronization (in bimanual tapping). In the ACCG, frontal, central and parietal ICohs were shown to be smaller, while temporal ICohs were larger under all conditions (see also Koeda, T., Knyazeva, M., Jonkman, J., Njiokiktjien, C., De Sonneville, L., Vildavsky, V., 1995. The resting EEG in acallosal children: compensatory left hemisphere mechanisms? Electroencephalogr. Clin. Neurophysiol. 95, 397 – 407). The effect was most pronounced in the EEG  band. The sagittal HCohs, including fronto-central, fronto-parietal, and centro-parietal HCohs within both hemispheres, were larger in the ACCG, whereas temporal HCoh (fronto-temporal, centro-temporal, parieto-temporal and occipito-temporal) were smaller, suggesting rearrangement of intracortical activity associated with callosal agenesis. Tapping induced an increase in ICoh and HCoh between frontal, central and parietal areas in the NG, and weak enhancement only in the left temporal HCoh in the ACCG. The  band, the most reactive band in the NG, was ‘silent’ in the ACCG, suggesting deviant cortical function during motor activity as well. © 1997 Elsevier Science B.V. Keywords: Callosal agenesis; EEG; Coherence; Functional compensation; Fingertapping; Interhemispheric asymmetry 1. Introduction Deviant intrahemispheric connectivity patterns reflected in EEG coherence in the resting state in acal- losal children and adults [21] suggest that functions requiring interhemispheric collaboration in the normal brain could be realized within the left hemisphere of acallosals. Such an assumption, however, applies pri- marily to relatively well-compensated functions. How- ever, deficient functions, including bimanual dyscoordination, remain open to the question as to whether their deficiency can be explained by a ‘crowd- ing effect’ within one hemisphere — i.e. an overrepresen- tation of functions within a relatively too small neural space — or by interhemispheric disconnection. Biman- ual dyscoordination has been repeatedly demonstrated in patients with disconnected hemispheres [16,33,34,42], suggesting a causal link with agenesis of the corpus callosum (ACC). Tapping tasks, combining uni- and bimanual conditions with additional demands on inter- hemispheric interaction in the latter condition, provide * Corresponding author. Tel.: +31 20 4440859; fax: +31 20 4440844; e-mail: Kindergen@azvu.nl 0166-4328/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0166-4328(97)00070-3