Elina Pihko

Cortical responses of infants with and without a genetic risk for dyslexia: II. Group effects.

Infants born to families with a background of developmental dyslexia have an increased risk of becoming dyslexic. In our previous study no major group or stimulus effects in the event-related potentials (ERPs) of at-risk and control infants were found until the age of 6 months. However, in the current study, when we made the stimulus presentation rate slower, the ERPs to the short deviant /ka/ were different from those to the long standard /kaa/ stimulus already in newborns. In addition, clear group differences in the ERPs were found. The results demonstrate that infants born with a high familial risk for dyslexia process speech/auditory stimulus durations differently from control infants at birth.

Brain Responses to Changes in Speech Sound Durations Differ Between Infants With and Without Familial Risk for Dyslexia

A specific learning disability, developmental dyslexia, is a language-based disorder that is shown to be strongly familial. Therefore, infants born to families with a history of the disorder are at an elevated risk for the disorder. However, little is known of the potential early markers of dyslexia. Here we report differences between 6-month-old infants with and without high risk of familial dyslexia in brain electrical activation generated by changes in the temporal structure of speech sounds, a critical cueing feature in speech. We measured event-related brain responses to consonant duration changes embedded in ata pseudowords applying an oddball paradigm, in which pseudoword tokens with varying /t/ duration were presented as frequent standard (80%) or as rare deviant stimuli (each 10%) with an interval of 610 msec between the stimuli. The infants at risk differ from control infants in both their initial responsiveness to sounds per se and in their change-detection responses dependent on the stimulus context. These results show that infants at risk due to a familial background of reading problems process auditory temporal cues of speech sounds differently from infants without such a risk even before they learn to speak.

Determinants of dominance: is language laterality explained by physical or linguistic features of speech?

The nature of cerebral asymmetry of the language function is still not fully understood. Two main views are that laterality is best explained (1) by left cortical specialization for the processing of spectrally rich and rapidly changing sounds, and (2) by a predisposition of one hemisphere to develop a module for phonemes. We tested both of these views by investigating magnetic brain responses to the same brief acoustic stimulus, placed in contexts where it was perceived either as a noise burst with no resemblance of speech, or as a native language sound being part of a meaningless pseudoword. In further experiments, the same acoustic element was placed in the context of words. We found reliable left hemispheric dominance only when the sound was placed in word context. These results, obtained in a passive odd-ball paradigm, suggest that neither physical properties nor phoneme status of a sound are sufficient for laterality. In order to elicit left lateralized cortical activation in normal right-handed individuals, a rapidly changing spectrally rich sound with phoneme status needs to be placed in the context of frequently encountered larger language elements, such as words. This demonstrates that language laterality is bound to the processing of sounds as units of frequently occurring meaningful items and can thus be linked to the processes of learning and memory trace formation for such items rather than to their physical or phonological properties.

Maturational effects on newborn ERPs measured in the mismatch negativity paradigm

The mismatch negativity (MMN) component of event-related potentials (ERPs), a measure of passive change detection, is suggested to develop early in comparison to other ERP components, and an MMN-like response has been measured even from preterm infants. The MMN response in adults is negative in polarity at about 150-200 ms. However, the response measured in a typical MMN paradigm can also be markedly different in newborns, even opposite in polarity. This has been suggested to be related to maturational factors. To verify that suggestion, we measured ERPs of 21 newborns during quiet sleep to rarely occurring deviant tones of 1100 Hz (probability 12%) embedded among repeated standard tones of 1000 Hz in an oddball sequence. Gestational age (GA) and two cardiac measures, vagal tone (V) and heart period (HP), were used as measures of maturation. GA and HP explained between 36% and 42% of the total variance of the individual ERP peak amplitude (the largest deflection of the difference wave at a time window of 150-375 ms) at different scalp locations. In the discriminant function analyses, GA and HP as classifying variables differentiated infants in whom the peak of the difference wave had positive polarity from those with a negative polarity at an accuracy level ranging from 72% to 91%. These results demonstrate that during quiet sleep, maturational factors explain a significant portion of the ERP difference wave amplitude in terms of its polarity, indicating that the more mature the ERPs are, the more positive the amplitude. The present study suggests that maturational effects should be taken into account in ERP measurements using MMN paradigms with young infants.

Music and speech listening enhance the recovery of early sensory processing after stroke

Our surrounding auditory environment has a dramatic influence on the development of basic auditory and cognitive skills, but little is known about how it influences the recovery of these skills after neural damage. Here, we studied the long-term effects of daily music and speech listening on auditory sensory memory after middle cerebral artery (MCA) stroke. In the acute recovery phase, 60 patients who had middle cerebral artery stroke were randomly assigned to a music listening group, an audio book listening group, or a control group. Auditory sensory memory, as indexed by the magnetic MMN (MMNm) response to changes in sound frequency and duration, was measured 1 week (baseline), 3 months, and 6 months after the stroke with whole-head magnetoencephalography recordings. Fifty-four patients completed the study. Results showed that the amplitude of the frequency MMNm increased significantly more in both music and audio book groups than in the control group during the 6-month poststroke period. In contrast, the duration MMNm amplitude increased more in the audio book group than in the other groups. Moreover, changes in the frequency MMNm amplitude correlated significantly with the behavioral improvement of verbal memory and focused attention induced by music listening. These findings demonstrate that merely listening to music and speech after neural damage can induce long-term plastic changes in early sensory processing, which, in turn, may facilitate the recovery of higher cognitive functions. The neural mechanisms potentially underlying this effect are discussed.

Somatosensory evoked potentials and magnetic fields elicited by tactile stimulation of the hand during active and quiet sleep in newborns.

OBJECTIVE Our objective was to characterize the effects of sleep stages on tactile somatosensory evoked responses in full-term newborns. METHODS Somatosensory evoked potentials (SEPs) and magnetic fields (SEFs) to tactile stimulation of the tip of the index finger and/or thenar eminence were measured from 14 healthy newborns. The stimulus was a gentle tap produced by a moving membrane driven by an air-pressure pulse. RESULTS SEPs and SEFs to tactile stimulation of the skin were similar in waveform and latency to SEPs known to be produced by electrical stimulation of the fingertip of neonates. The two most distinguishable positive deflections of SEPs, P1 and P2, within 300 ms of the stimulation, and their magnetic counterparts were clearly smaller in active compared to quiet sleep. CONCLUSIONS Our study demonstrates for the first time that it is possible to record SEFs in neonates, and that clear late cortical somatosensory responses are produced by tactile stimulation. In addition, the effect of sleep stage on these responses indicates differences in the processing of the incoming information, at least in the somatosensory modality, in active and quiet sleep. SIGNIFICANCE Tactile stimulation may be useful as a completely non-invasive technique for studying the physiology of the somatosensory system in neonates. Methodologically, since the effect of sleep stage is profound, one must carefully monitor the sleep stages in studies of event-related responses in newborns, or else this effect may confound the phenomena being studied.

Observing touch activates human primary somatosensory cortex

We used magnetoencephalography to show that the human primary somatosensory (SI) cortex is activated by mere observation of touch. Somatosensory evoked fields were measured from adult human subjects in two conditions. First, the experimenter touched the subject’s right hand with her index finger (Experienced touch). In the second condition, the experimenter touched her own hand in a similar manner (Observed touch). Minimum current estimates were computed across three consecutive 300‐ms time windows (0–300, 300–600 and 600–900 ms) with respect to touch onset. During ‘Experienced touch’, as expected, the contralateral (left) SI cortex was strongly activated in the 0–300 ms time window. In the same time window, statistically significant activity also occurred in the ipsilateral SI, although it was only 2.5% of the strength of the contralateral activation; the ipsilateral activation continued in the 300–600 ms time window. During ‘Observed touch’, the left SI cortex was activated during the 300–600 ms interval; the activation strength was 7.5% of that during the significantly activated period (0–300 ms) of ‘Experienced touch’. The results suggest that when people observe somebody else being touched, activation of their own somatosensory circuitry may contribute to understanding of the other person’s somatosensory experience.

Experiencing art: the influence of expertise and painting abstraction level

How does expertise influence the perception of representational and abstract paintings? We asked 20 experts on art history and 20 laypersons to explore and evaluate a series of paintings ranging in style from representational to abstract in five categories. We compared subjective esthetic judgments and emotional evaluations, gaze patterns, and electrodermal reactivity between the two groups of participants. The level of abstraction affected esthetic judgments and emotional valence ratings of the laypersons but had no effect on the opinions of the experts: the laypersons’ esthetic and emotional ratings were highest for representational paintings and lowest for abstract paintings, whereas the opinions of the experts were independent of the abstraction level. The gaze patterns of both groups changed as the level of abstraction increased: the number of fixations and the length of the scanpaths increased while the duration of the fixations decreased. The viewing strategies – reflected in the target, location, and path of the fixations – however indicated that experts and laypersons paid attention to different aspects of the paintings. The electrodermal reactivity did not vary according to the level of abstraction in either group but expertise was reflected in weaker responses, compared with laypersons, to information received about the paintings.

Neurodynamic Studies on Emotional and Inverted Faces in an Oddball Paradigm

The detection of a change in a face stimulus was studied in an oddball paradigm. Event-related potentials (ERPs) and MEG responses to face stimuli were recorded in four conditions: 1) happy standard, neutral deviant; 2) neutral standard, neutral deviant; 3) inverted happy standard, inverted neutral deviant; 4) inverted neutral standard, inverted neutral deviant. In all conditions, the target was a face with glasses. Neutral deviants elicited a negative deflection (with a maximum around 280 ms) in ERP and MEG responses, an effect similar to auditory mismatch negativity. Face inversion diminished deviance-related negativity, implying an important role of face recognition in the observed effect. Emotional content and larger physical differences between stimuli in conditions 1 and 3 compared to conditions 2 and 4 did not show statistically significant effect on the neutral-deviant-related negativity.

Immaturity of somatosensory cortical processing in human newborns.

The development of the early component of somatosensory evoked potentials (SEPs) from the neonatal N1 to adult N20 response has previously been described. The main emphasis has been on the change in the response latency during maturation. We used magnetoencephalography (MEG) to characterize the cortical generators of the N1 and the subsequent response in healthy human newborns. Furthermore, we studied the maturation of tactile processing according to responses evoked by tactile stimulation of the index finger in newborns, 6-month-old babies and adults. This study provides evidence of specific differences in the somatosensory processing in neonates compared to that in adults. Although the initial cortical response to electrical median nerve stimulation in the newborns was similar in field distribution to the corresponding N20m in adults, the subsequent major deflection in the response waveform had the opposite polarity. Similar immaturity in cortical processing was seen in the tactile evoked fields in both the newborns and the 6-month-old infants compared with the adults. Our results indicate that although the somatosensory pathway in full-term newborns is sufficiently developed to supply the brain with tactile information, the cortical neuronal networks for processing the input may not function in the same way as in adults.