Brain responses to audiovisual speech mismatch in infants are associated with individual differences in looking behaviour.

Research on audiovisual speech integration has reported high levels of individual variability, especially among young infants. In the present study we tested the hypothesis that this variability results from individual differences in the maturation of audiovisual speech processing during infancy. A developmental shift in selective attention to audiovisual speech has been demonstrated between 6 and 9 months with an increase in the time spent looking to articulating mouths as compared to eyes (Lewkowicz & Hansen-Tift. (2012) Proc. Natl Acad. Sci. USA, 109, 1431-1436; Tomalski et al. (2012) Eur. J. Dev. Psychol., 1-14). In the present study we tested whether these changes in behavioural maturational level are associated with differences in brain responses to audiovisual speech across this age range. We measured high-density event-related potentials (ERPs) in response to videos of audiovisually matching and mismatched syllables /ba/ and /ga/, and subsequently examined visual scanning of the same stimuli with eye-tracking. There were no clear age-specific changes in ERPs, but the amplitude of audiovisual mismatch response (AVMMR) to the combination of visual /ba/ and auditory /ga/ was strongly negatively associated with looking time to the mouth in the same condition. These results have significant implications for our understanding of individual differences in neural signatures of audiovisual speech processing in infants, suggesting that they are not strictly related to chronological age but instead associated with the maturation of looking behaviour, and develop at individual rates in the second half of the first year of life.

Measurement of ERP latency differences: a comparison of single-participant and jackknife-based scoring methods.

We used computer simulations to evaluate different procedures for measuring changes in the onset latency of a representative range of event-related components (the auditory and visual N1, P3, N2pc, and the frequency-related P3 difference wave). These procedures included several techniques to determine onset latencies combined with approaches using both single-participant average waveforms and jackknife-subsample average waveforms. In general, the jackknife-based approach combined with the relative criterion technique or combined with the fractional area technique (J.C. Hansen & S.A. Hillyard, 1980; S.J. Luck, 2005) provided the most accurate method and the greatest statistical power, with no inflation of Type I error rate.

Decomposing stimulus and response component waveforms in ERP.

Event-related potentials (ERPs) are evoked brain potentials that are averaged across many trial repetitions with individual trials aligned (i.e. time-locked) to a specific behavioral event, typically the onset of the stimulus (s-lock) or the onset of the behavioral response (r-lock). These evoked potential averages may reflect brain activities during the stimulus encoding/analyzing stage (stimulus component waveform, or 'S-component'), during the response preparation/production stage (response component waveform, or 'R-component'), or a combination thereof. In the stimulus-locked average of the ensemble of the recorded waveforms (i.e. in the s-locked ERP), the contribution of an R-component will be convoluted, due to the trial-by-trial variance in reaction time (RT): so will an S-component in the r-locked ERP. It is shown here that the knowledge of (1) the s-locked and r-locked ERP waveforms constructed from the same ensemble of trials and (2) the RT distribution of this ensemble allows us to determine whether the recorded potential results from a single S-component, a single R-component, or a single intermediate ('decisional' or D-) component related to the transition of the two stochastically independent stages. If it can be assumed that the evoked potential is the result of a linear summation of an S-component and an R-component, then there is a unique recovery into these two components, such that the reconstructed waveform on an individual trial is a superposition of the two components with their relative offset determined by the RT of that trial and the ensemble average is the experimentally obtained s-locked and r-locked ERP waveforms. Two independent methods can be used to recover those components, one based on Fourier transform techniques which was first proposed by Hansen (1983) in the context of ERP component isolation and the other based on a recursive iteration approach through which the contamination of the R or S-component is successively removed from the s-locked or r-locked ERP waveforms, respectively. The iterative procedure is analytically proven to converge to the Fourier-based solution, demonstrating the equivalence of the two approaches. Finally, if the condition of a single intermediate D-component is satisfied, then one can recover this component waveform along with the probability distributions of the relative durations of the two underlying linear stages; however, there is always an equivalent pair of S- and R-component which also satisfy the same data set (s-locked and r-locked ERP waveforms and the overall RT distribution). In this case, the S/R-component assumption and the D-component assumption cannot be distinguished solely on the ground of the available data set. The technique developed here outlines the assumptions and the boundary conditions upon which ensemble ERP waveforms are to be analyzed and interpreted in terms of processing mechanisms related to stimulus, to response, or to the transition between the two.

Comparing the anticonvulsive effects of dapsone on amygdala-kindled seizures and hippocampal-kindled seizures in rats.

Dapsone, an antileprosy drug, was administered to rats with amygdala (AM)-kindled seizures or hippocampal (HIPP)-kindled seizures to elucidate its anticonvulsive efficacy. Adult male Wistar rats were subjected to kindling stimulations 2 weeks after electrode-implantation. The subjects were tested once a day for 7 successive days after inducing three generalized (stage 5) seizures to study the effects of dapsone. Dapsone had an inhibitory effect on stage 5 seizures at 12.50 mg/kg in the AM-kindled rats and at 6.25 mg/kg and 9.375 mg/kg in the HIPP-kindled rats. Thus, there was a distinct difference in the effective dose for generalized seizures between the AM-kindled rats and the HIPP-kindled rats. The inhibitory action of dapsone on stage 5 seizures may be due mainly to the elevation of the afterdischarge-triggering threshold at the stimulation site of the AM or HIPP. Such inhibitory action appears prominently at serum concentrations of about 13 micrograms/ml in AM-kindled rats and about 6 micrograms/ml in HIPP-kindled rats. The level of 6 micrograms/ml almost equals the therapeutic serum concentration of dapsone used in the treatment of leprosy.

[Study of afferent conduction in the external saphenous nerve using the method of evoked cerebral potentials]. / Etude de la conduction afférente dans le nerf saphène externe par le technique des potentiels évoqués cérébraux

By the comparison of nerve action potentials and cerebral potentials evoked by the same electrical stimulus the propagation of the somaesthetic impulse to the cerebral cortex can be evaluated. This technique was applied to the fibres of the sural nerve in normal subjects and in patients presenting various lesions of the peripheral and central nervous system. Evoked cerebral potential afforded valuable data when it was not possible to record the nerve action potentials or when the lesion involved the central segment of the afferent pathway.

Nerve conduction studies in leprosy.

Motor and sensory nerve conduction studies have been performed on the peripheral nerves in the upper and lower limbs of 30 control subjects, and 36 subjects with leprosy from the Aboriginal population of the Northern Territory of Australia. Impairment of conduction was demonstrated in the vast majority of clinically abnormal nerves, and a large proportion of nerves which appeared clinically to be uninvolved. In a third group of subjects, abnormal conduction was demonstrated in a significant number of nerves which were considered to be clinically enlarged but in whom the diagnosis was initially in doubt. The majority of these patients were subsequently proven to have leprosy. It is concluded that nerve conduction studies are of considerable value in the diagnosis and management of leprosy.