MMN

The current study investigated neural refractory e¡ects in children (8^12 years) with reading disorders and a control group. Cortical responses (P1and N250) to the sound /da / were measured at inter-stimulus intervals of 538, 1072 and 2152 ms. As expected, owing to slow neural recovery periods, both groups showed longer cortical response latencies at the shortest interstimulus interval of 538 ms. N250 showed a slower neural refractory period at the short interstimulus interval (538 ms) for children with reading disorders than the control group, however. Only control group children showed interhemispheric di¡erences for the N250 peak. No group di¡erences were evident for P1. The results suggest that children with reading disorders have di¡erent and slower underlying neural responses than typically developing children. NeuroReport18:133^136

associative functions and aspects of attention and perception (5). Hanagasi et al. (6) suggested, on the basis of results obtained using this approach, that ALS patients in the early stages of disease present a sub-clinical impairment in cognitive functions, particularly in executive functions. Gil et al. found a prolonged latency of the N2 and P3 components and, in keeping with Paulus et al. ' s results (8), hypothesized an impairment particularly in working memory. However, other authors (9,10) have hypothesized an involvement of attentional resources related to auditory selective attention. Raggi et al. (11), using a passive auditory P3 paradigm, reported that the early phases of the attentive discrimination, even the involuntary pre-attentive phase, may be impaired in ALS patients, as expressed by the reduced amplitude of the MMN and the N1 components, observing that the latter Abstract Our objective was to evaluate attentional processing with respect to the clinical-onset subtype in amyotrophic lateral sclerosis (ALS) using event-related potentials (ERPs). Thirty-three non-demented ALS patients (22 spinal onset, 11 bulbar onset) and 32 age-and gender-matched controls underwent a psychophysiological evaluation. Mismatch Negativity (MMN), P300 components and Contingent Negative Variation (CNV) were obtained. Latencies and amplitudes of the MMN, P3a and P3b waves and CNV amplitude were then evaluated. Clinical parameters were correlated with ERP data. No differences emerged between ALS patients and controls with regard to the MMN and P3b components. N1-P3a interpeak latency (Fz, p ϭ 0.003; Cz, p ϭ 0.001; Pz, p ϭ 0.002) was longer in ALS-b than in ALS-s. Total CNV area (Cz, p ϭ 0.01) and W1-CNV area were signifi cantly reduced (Cz, p ϭ 0.05; Pz, p ϭ 0.03) in ALS-b with respect to the one of the controls, while no differences were found between ALS-s patients and controls. In conclusion, automatic pre-attentive processing of stimuli seems to be preserved in ALS. However, a signifi cant delay in the time-course of selective attentive processing and a diffi culty in initiating and sustaining attention may be present in ALS-b, which points to a possible dysfunction in the frontal neural network that responds to novelty and to abnormal integration of associative functions. This attentional impairment should be taken in account while developing alternative communicative strategies in ALS patients.

Repetitive transcranial magnetic stimulation (rTMS) is considered a powerful method for the study of the relationships between cortical activity and cognitive processes. Previous ERPs studies that focused on P300 response have shown that inhibitory/excitatory effects on prefrontal cortex (PFC), induced by low-and highfrequency rTMS, were able to modulate controlled but not automatic information processing. The present study assessed the impact of inhibition over left and right PFC induced by rTMS on mismatch negativity (MMN), which is known to represent automatic cerebral processes for detecting change. Auditory MMN was recorded in 20 subjects before and after application of left and right PFC 1-Hz rTMS for 15 min. MMN was also recorded before and after a sham-occipital 1-Hz rTMS as control condition. Results showed that 1-Hz rTMS induced no modification to either MMN latency or amplitude. In addition, N100 and P200 components to the frequent tones were not affected by rTMS. These results are consistent with previous findings showing that rTMS over both PFC is unable to disrupt automatic information processing. However, since two sites were stimulated in the present study, no definite conclusions about the inability of rTMS to disrupt automatic processing can be made. N200) were not altered by rTMS. Taken together, these findings could suggest that cortical inhibition induced by slow rTMS over PFC could affect principally the controlled cognitive processes (i.e., P300).

The present study systematically compared the neural and behavioral accuracy of discriminating a frequency change (''deviant'') in a repetitive tone (''standard'') across a frequency range of 250 -4000 Hz. The sound structure (pure sinusoidal vs. harmonically rich tones) and the magnitude of frequency change (2.5%, 5%, 10%, 20%) were also varied. The accuracy of neural frequency-change detector was determined by comparing the auditory event-related potentials (ERP) elicited by deviant and standard stimuli in the absence of attention. In a separate behavioral task, subjects were to indicate when they noticed a frequency change. The ranges of the across-subject means of ERP parameters across the conditions were: the mismatch negativity (MMN) amplitude À 0.9 to À 4.9 AV, latency 125 -218 ms, the P3a amplitude 0.3 -3.2 AV, latency 239 -304 ms. The ERP latency was shortest for the standard-stimulus frequency from 1000 to 2000 Hz suggesting that automatic frequency discrimination was the most accurate in that range. The ERP latencies and amplitudes correlated with the hit rate (HR) and reaction time (RT), with highest correlation found between the MMN amplitude and the HR (r = 0.8). The harmonical tones elicited MMN and P3a with shorter latencies and larger amplitudes, than did pure sinusoidal tones in all frequency bands. The results may have implication to pitch-perception theories. D