Atypical organisation of the auditory cortex in dyslexia as revealed by MEG

Abstract

Neuroanatomical and -radiological studies have converged to suggest an atypical organisation in the temporal bank of the left-hemispheric Sylvian fissure for dyslexia. Against the background of this finding, we applied high temporal resolution magnetoencephalography (MEG) to investigate functional aspects of the left-hemispheric auditory cortex in 11 right-handed dyslexic children (aged 8-13 years) and nine matched normal subjects (aged 8 -14 years). Event-related field components during a passive oddball paradigm with pure tones and consonant -vowel syllables were evaluated. The first major peak of the auditory evoked response, the M80, showed identical topographical distributions in both groups. In contrast, the generating brain structures of the later M210 component were located more anterior to the earlier response in children with dyslexia only. Control children exhibited the expected activation of more posterior source locations of the component that appeared later in the processing stream. Since the group difference in the relative location of the M210 source seemed to be independent of stimulus category, it is concluded that dyslexics and normally literate children differ as to the organisation of their left-hemispheric auditory cortex.

Using magnetoencephalography in assessing auditory skills in infants and children

“…For example, Breier et al (2001) succeeded in determining the language-dominant hemisphere with MEG in children. The results in dyslexic children (Sarkari et al, 2002;Breier et al, 2003;Heim et al, 2000Heim et al, , 2003 show that the differences in the brain networks allocated to the speech perception tasks in dyslexic and control children can be observed in MEG.…”

Maturation of the cortical auditory evoked potential in infants and young children

“…In general, spectrally complex sounds, such as speech tokens, evoke larger responses than simple tones as indicated by fMRI (Binder et al, 2000), single photon emission tomography (Ottaviani et al, 1997) or by the amplitude of the electrical (Lenard et al, 1969;Tiitinen et al, 1999) and neuromagnetic response (Heim et al, 2000;Pantev et al, 1998). This effect was seen for P 2 and N 2 in Newborns, for N 1 in Toddlers, for N 2 in Children and N 1 and P 2 for Adults.…”

Reorganization of Human Cerebral Cortex: The Range of Changes Following Use and Injury

“…Deviances in hemispheric asymmetry of temporal lobe functional organization in these children (Heim and others 2000(Heim and others , 2001(Heim and others , 2003(Heim and others , 2004 suggested that an atypical organization of perisylvian regions, in particular the planum temporale, may continue into adulthood. The findings cannot be attributed to gross anatomical variations but rather indicate an abnormal functional organization of auditory cortex in children with dyslexia.…”

“…In a series of magnetoencephalographic investigations, Sabine Heim from our lab demonstrated that sources generated by stop consonant-vowel syllables (at 200-ms latency) differed in their location in the auditory cortex between children with dyslexia and control children (Heim and others 2000). Deviances in hemispheric asymmetry of temporal lobe functional organization in these children (Heim and others 2000(Heim and others , 2001(Heim and others , 2003(Heim and others , 2004 suggested that an atypical organization of perisylvian regions, in particular the planum temporale, may continue into adulthood.…”