Biomedical subjects

Samu Taulu

Publications and source records attributed to Samu Taulu.

5 recordsLinked to original sources

PubMed2006

Infant speech perception activates Broca's area: a developmental magnetoencephalography study.

Discriminative responses to tones, harmonics, and syllables in the left hemisphere were measured with magnetoencephalography in neonates, 6-month-old infants, and 12-month-old infants using the oddball paradigm. Real-time head position tracking, signal space separation, and head position standardization were applied to secure quality data for source localization. Minimum current estimates were calculated to characterize infants' cortical activities for detecting sound changes. The activation patterns observed in the superior temporal and inferior frontal regions provide initial evidence for the developmental emergence early in life of a perceptual-motor link for speech perception that may depend on experience.

Acoustic Stimulation↗

PubMed2005

Short-term memory functions of the human fetus recorded with magnetoencephalography.

Studies in fetuses and in prematurely born infants show that auditory discriminative skills are present prior to birth. The magnetic fields generated by the fetal brain activity pass the maternal tissues and, despite their weakness, can be detected externally using MEG. Recent studies on the auditory evoked magnetic responses show that the fetal brain responds to sound onset. In contrast, higher-level auditory skills, such as those involving discriminative and memory functions, were not so far studied in fetuses with MEG. Here we show that fetal responses related to discriminating sounds can be recorded, implicating that the auditory change-detection system is functional. These results open new views to developmental neuroscience by enabling one to determine the sensory capabilities as well as the extent and accuracy of the short-term memory system of the fetus, and, further, to follow the development of these crucial processes.

Adult↗

PubMed2004

Magnetoencephalography is feasible for infant assessment of auditory discrimination.

Magnetoencephalography (MEG) detects the brain's magnetic fields as generated by neuronal electric currents arising from synaptic ion flow. It is noninvasive, has excellent temporal resolution, and it can localize neuronal activity with good precision. For these reasons, many scientists interested in the localization of brain functions have turned to MEG. The technique, however, is not without its drawbacks. Those reluctant to employ it cite its relative awkwardness among pediatric populations because MEG requires subjects to be fairly still during experiments. Due to these methodological challenges, infant MEG studies are not commonly pursued. In the present study, MEG was employed to study auditory discrimination in infants. We had two goals: first, to determine whether reliable results could be obtained from infants despite their movements; and second, to improve MEG data analysis methods. To get more reliable results from infants we employed novel hardware (real-time head-position tracking system) and software (signal space separation method, SSS) solutions to better deal with noise and movement. With these solutions, the location and orientation of the head can be tracked in real time and we were able to reduce noise and artifacts originating outside the helmet significantly. In the present study, these new methods were used to study the biomagnetic equivalents of event-related potentials (ERPs) in response to duration changes in harmonic tones in sleeping, healthy, full-term newborns. Our findings indicate that with the use of these new analysis routines, MEG will prove to be a very useful and more accessible experimental technique among pediatric populations.

Acoustic Stimulation↗

PubMed2004

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.

Electroencephalography↗

PubMed2004

Suppression of interference and artifacts by the Signal Space Separation Method.

Multichannel measurement with hundreds of channels oversamples a curl-free vector field, like the magnetic field in a volume free of sources. This is based on the constraint caused by the Laplace's equation for the magnetic scalar potential; outside of the source volume the signals are spatially band limited. A functional solution of Laplace's equation enables one to separate the signals arising from the sphere enclosing the interesting sources, e.g. the currents in the brain, from the magnetic interference. Signal space separation (SSS) is accomplished by calculating individual basis vectors for each term of the functional expansion to create a signal basis covering all measurable signal vectors. Because the SSS basis is linearly independent for all practical sensor arrangements, any signal vector has a unique SSS decomposition with separate coefficients for the interesting signals and signals coming from outside the interesting volume. Thus, SSS basis provides an elegant method to remove external disturbances. The device-independent SSS coefficients can be used in transforming the interesting signals to virtual sensor configurations. This can also be used in compensating for distortions caused by movement of the object by modeling it as movement of the sensor array around a static object. The device-independence of the decomposition also enables physiological DC phenomena to be recorded using voluntary head movements. When used with properly designed sensor array, SSS does not affect the morphology or the signal-to-noise ratio of the interesting signals.

Artifacts↗