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Biomedical subjects

J Huttunen

Publications and source records attributed to J Huttunen.

At least 19 recordsLinked to original sources
PubMed2005

Interaction of mobile phones with superficial passive metallic implants.

The dosimetry of exposure to radiofrequency (RF) electromagnetic (EM) fields of mobile phones is generally based on the specific absorption rate (SAR, W kg(-1)), which is the electromagnetic energy absorbed in the tissues per unit mass and time. In this study, numerical methods and modelling were used to estimate the effect of a passive, metallic (conducting) superficial implant on a mobile phone EM field and especially its absorption in tissues in the near field. Two basic implant models were studied: metallic pins and rings in the surface layers of the human body near the mobile phone. The aim was to find out 'the worst case scenario' with respect to energy absorption by varying different parameters such as implant location, orientation, size and adjacent tissues. Modelling and electromagnetic field calculations were carried out using commercial SEMCAD software based on the FDTD (finite difference time domain) method. The mobile phone was a 900 MHz or 1800 MHz generic phone with a quarter wave monopole antenna. A cylindrical tissue phantom models different curved sections of the human body such as limbs or a head. All the parameters studied (implant size, orientation, location, adjacent tissues and signal frequency) had a major effect on the SAR distribution and in certain cases high local EM fields arose near the implant. The SAR values increased most when the implant was on the skin and had a resonance length or diameter, i.e. about a third of the wavelength in tissues. The local peak SAR values increased even by a factor of 400-700 due to a pin or a ring. These highest values were reached in a limited volume close to the implant surface in almost all the studied cases. In contrast, without the implant the highest SAR values were generally reached on the skin surface. Mass averaged SAR(1 g) and SAR(10 g) values increased due to the implant even by a factor of 3 and 2, respectively. However, at typical power levels of mobile phones the enhancement is unlikely to be problematic.

Adipose Tissue↗
PubMed2005

Superresolution ultrasound imaging using back-projected reconstruction.

An ultrasound technique for imaging objects significantly smaller than the source wavelength is investigated. Signals from a focused beam are recorded over an image plane in the acoustic farfield and backprojected in the wave-vector domain to the focal plane. A superresolution image recovery method is then used to analyze the Fourier spatial frequency spectrum of the signal in an attempt to deduce the location and size of objects in this plane. The physical foundation for the method is rooted in the fact that high spatial frequencies introduced by the object in fact affect the lower (nonevanescent) spatial frequencies of the overall signal. The technique achieves this by using a priori measurements of the ultrasound focus in water, which gives full spectral information about the image source. A guess is then made regarding the size and location of the object that distorted the field, and this is convolved with the a priori measurement, thus creating a candidate image. A large number of candidates are generated and the one whose spectrum best matches the uncorrected image is accepted. The method is demonstrated using 0.34- and 0.60-mm wires with a focused 1.05-MHz ultrasound signal and then a human hair (approximately 0.03 mm) with a 4.7-MHz signal.

Acoustics↗
PubMed2005

Abnormal crossing of the optic fibres shown by evoked magnetic fields in patients with ocular albinism with a novel mutation in the OA1 gene.

AIM: To perform genealogical and clinical studies in Finnish families with X linked ocular albinism (OA1), including characterisation of the potential misrouting of optic fibres by evaluating visual evoked magnetic fields (VEFs), and to determine the mutation behind the disease. METHODS: Three families with OA1 were clinically examined. VEFs were measured in two affected males and in one female carrier to characterise the cortical activation pattern after monocular visual stimulation. The neuronal sources of the VEFs were modelled with equivalent current dipoles (ECDs) in a spherical head model. All coding exons of the OA1 gene were screened for mutations by single strand conformation analysis and direct polymerase chain reaction sequencing. RESULTS: Genealogical studies revealed that the three families were all related. The affected males had foveal hypoplasia with reduced visual acuity varying from 20/200 to 20/50, variable nystagmus, iris transillumination, and hypopigmentation of the retinal pigment epithelium. The ECD locations corresponding to the VEFs revealed abnormal crossing of the optic fibres in both affected males, but not in the carrier female. A novel point mutation, leading to a STOP codon, was identified in the fifth exon of the OA1 gene. CONCLUSIONS: The data indicate that the novel mutation 640C>T in the OA1 gene is the primary cause of the eye disease in the family studied. VEFs with ECD analysis was successfully used to demonstrate abnormal crossing of the optic fibres.

Adult↗
PubMed2004

EEG minimum-norm estimation compared with MEG dipole fitting in the localization of somatosensory sources at S1.

OBJECTIVE: Dipole models, which are frequently used in attempts to solve the electromagnetic inverse problem, require explicit a priori assumptions about the cerebral current sources. This is not the case for solutions based on minimum-norm estimates. In the present study, we evaluated the spatial accuracy of the L2 minimum-norm estimate (MNE) in realistic noise conditions by assessing its ability to localize sources of evoked responses at the primary somatosensory cortex (SI). METHODS: Multichannel somatosensory evoked potentials (SEPs) and magnetic fields (SEFs) were recorded in 5 subjects while stimulating the median and ulnar nerves at the left wrist. A Tikhonov-regularized L2-MNE, constructed on a spherical surface from the SEP signals, was compared with an equivalent current dipole (ECD) solution obtained from the SEFs. RESULTS: Primarily tangential current sources accounted for both SEP and SEF distributions at around 20 ms (N20/N20m) and 70 ms (P70/P70m), which deflections were chosen for comparative analysis. The distances between the locations of the maximum current densities obtained from MNE and the locations of ECDs were on the average 12-13 mm for both deflections and nerves stimulated. In accordance with the somatotopical order of SI, both the MNE and ECD tended to localize median nerve activation more laterally than ulnar nerve activation for the N20/N20m deflection. Simulation experiments further indicated that, with a proper estimate of the source depth and with a good fit of the head model, the MNE can reach a mean accuracy of 5 mm in 0.2-microV root-mean-square noise. CONCLUSIONS: When compared with previously reported localizations based on dipole modelling of SEPs, it appears that equally accurate localization of S1 can be obtained with the MNE. SIGNIFICANCE: MNE can be used to verify parametric source modelling results. Having a relatively good localization accuracy and requiring minimal assumptions, the MNE may be useful for the localization of poorly known activity distributions and for tracking activity changes between brain areas as a function of time.

Adult↗
PubMed2003

PROD-screen--a screen for prodromal symptoms of psychosis.

The aim of this study was to describe the PROD-screen, an instrument for screening prodromal symptoms indicating risk for psychotic conversion in the near future. PROD-screen consists of 29 questions assessing performance and symptoms. Clinical construct validity was tested by comparing scores from the unselected general population (GP, n = 64) with those of general psychiatric patients from a community mental health centre (CMHC, n = 107). The concordant validity of PROD-screen for prodromal symptoms of psychosis was assessed in a large epidemiologically mixed sample of research subjects (n = 132) by comparing PROD-screen scores with the prodromal diagnosis made by Structured Interview for Prodromal Symptoms as a gold standard. Using the cut-off point of 2/12 specific symptoms, PROD-screen gave correct classification of prodromal status in 77% of cases, distinguishing prodromal from non-prodromal subjects with reasonable sensitivity (80%) and specificity (75%) in the epidemiologically mixed sample. According to subsample analysis PROD-screen functions well with first-degree relatives of schizophrenic patients and probably also with general population samples, but not with psychiatric outpatients. In conclusion, PROD-screen is a useful tool for screening prodromal symptoms of psychosis and selecting subjects for more extensive research interviews.

Adolescent↗
PubMed2002

Enlarged SI and SII somatosensory evoked responses in the CLN5 form of neuronal ceroid lipofuscinosis.

OBJECTIVES: To examine in detail the activation of the primary (SI) and secondary (SII) somatosensory cortex in CLN5, the Finnish variant of late infantile neuronal ceroid lipofuscinoses (NCL). METHODS: Somatory evoked magnetic fields were recorded with a 122-channel planar gradiometer in response to median nerve stimulation in 5 CLN5 patients (aged 8.8-16.7 years) and in 10 healthy age-matched controls. RESULTS: The first two responses from contralateral SI, N20m and P35m, were 6-20 times stronger in the patients than in the controls. The morphology of the subsequent deflections from SI was abnormal in the patients: a prominent N45m was detected, while the normally present P60m deflection was missing. In 4 patients the contra- and in two patients the ipsilateral SII responses were also enlarged. Furthermore, the SII activation was detected at shorter latency in patients than in controls. CONCLUSIONS: At SI, CLN5 is associated with a selective enhancement of the early cortical responses. We propose that the enlargement of N20m most likely reflects increased synchronous input from thalamus, whereas the altered morphology of the following responses may reflect defective interneuronal inhibition at the cortex. The enlargement of SII responses shows that the imbalance between excitation and inhibition in CLN5 extends outside the primary somatosensory areas.

Adolescent↗
PubMed2001

No evidence for dependence of early cortical auditory processing on dopamine D(2)-receptor modulation: a whole-head magnetoencephalographic study.

Magnetoencephalography (MEG) was used to determine the effect of neuroleptic challenge on brain responses in healthy subjects. In a double-blind, randomized, placebo-controlled, cross-over design study, the dopamine D(2) receptor antagonist haloperidol (2 mg) was given orally to 12 healthy volunteers. The middle-latency auditory evoked magnetic fields (MAEF) were recorded 3 h after administration of haloperidol or placebo with a whole-head 122-channel MEG. Haloperidol did not significantly affect MAEF responses. The dipole moments and source locations of the responses were not significantly influenced by haloperidol. These results suggest that dopamine D(2) receptors are not involved in the early phases of auditory cortical processing.

Adult↗
PubMed2001

Interhemispheric phase synchrony and amplitude correlation of spontaneous beta oscillations in human subjects: a magnetoencephalographic study.

Interhemispheric phase synchrony and amplitude correlation of beta oscillations were studied with MEG in a resting condition. The left and right hemisphere beta oscillations exhibited phase-locking with a phase-lag near zero degrees. The index of synchronization was strongest when these oscillations had large amplitude. Functionally, we interpret the phase synchrony on the basis of bilaterality of movement organization. A positive interhemispheric correlation was also found for the amplitude of spontaneous beta oscillations over long time intervals (> 1 s). The low-frequency correlation of spontaneous rhythmic activity may be the source of the low-frequency correlations of the hemodynamic responses in homologous areas that have been reported previously and have been interpreted as functional connectivity between these areas.

Beta Rhythm↗
PubMed2001

Scopolamine reduces the P35m and P60m deflections of the human somatosensory evoked magnetic fields.

Acetylcholine (ACh) is a potent neuromodulator in the brain with multiple, complex effects on neuronal function, most of which are mediated by muscarinic receptors. Generally, the most significant effect is excitation of pyramidal neurones and facilitation of responses to afferent stimulation. Much of the information on the ACh effects comes from studies utilizing in vitro or anesthetized in vivo preparations, while fewer data are available from awake animals or humans. We studied human somatosensory evoked magnetic fields (SEFs), which reflect summated postsynaptic currents in pyramidal neurones in area 3b, and in the opercular somatosensory cortex, when cholinergic transmission was modulated either by a central (scopolamine, 0.3 mg, i.v.) or peripheral (glycopyrrolate, 0.2 mg, i.v.) muscarinic antagonist. A randomized, double-blind, cross-over design was employed. SEFs were elicited by right median nerve stimulation at the wrist with constant-current pulses above motor threshold. The first excitatory cortical response from area 3b (N20m) was not affected by the central muscarinic blockade, while later P35m and P60m deflections were significantly reduced. The responses from the opercular somatosensory cortex showed some tendency toward reduction, but no significant alterations. The results show that somatosensory cortical processing can be modulated by muscarinic transmission at a relatively early stage. Relative membrane hyperpolarization of pyramidal neurons due to scopolamine (caused by blocking an ACh-induced tonic depolarization) is discussed as a possible mechanism underlying the observed effects.

Adult↗
PubMed2001

The Schizophrenia Suicide Risk Scale (SSRS): development and initial validation.

BACKGROUND: Estimations about the lifetime risk of suicide in schizophrenia vary between 4 and 10%. At present, there does not exist a suicide risk scale developed particularly for schizophrenic patients. The aims of the present study were to: (1) develop a clinically useful semi-structured scale for the estimation of short-term suicide risk among schizophrenic patients, and (2) to carry out an initial validation of the scale. METHODS: A 25-item Schizophrenia Suicide Risk Scale (SSRS) was constructed on the base of the literature. The SSRS scores of 69 living schizophrenic patients (LS group) were compared with the scores of 69 schizophrenic suicides (SS group) whose data had been collected previously from The Finnish nationwide and representative psychological autopsy study. Internal consistency of the SSRS was evaluated with Cronbach alpha. The most important SSRS items predicting suicide were identified with a logistic regression analysis. Sensitivity, specificity, positive predictive value, and negative predictive value of the SSRS in predicting suicide with various cut-off scores were calculated. RESULTS: In the final logistic regression model, the following SSRS items significantly predicted suicide: suicide plans communicated to someone during the past 3 months; one or more previous suicide attempts; loss of professional skills demanding job; depression observed during an interview; and suicide plans communicated during an interview. With high cut-off scores the specificity of the SSRS became satisfactory, but the sensitivity dropped below 32%. Internal consistency of the anamnestic history of the SSRS was low, which suggests that anamnestic risk factors for suicide in schizophrenia are multifactorial. Internal consistency of the interview-based items was high, and present state risk factors seemed to consist of two separate factors, depression-anxiety and irritability. CONCLUSIONS: The SSRS may be clinically useful in identifying schizophrenic patients with a particularly high risk for suicide. However, the SSRS seems not to be a practical screening instrument for suicide risk in schizophrenia, and it is probably impossible to construct a suicide risk scale with both high sensitivity and high specificity in this disorder.

Adolescent↗
PubMed2001

Auditory sensory memory and the cholinergic system: implications for Alzheimer's disease.

Auditory sensory memory represents one of the simplest types of short-term memory that can be studied electrophysiologically with mismatch negativity (MMN); a specific auditory event-related potential indexing automatic comparison of incoming stimuli to an existing memory trace. Previous results suggest that auditory sensory memory deteriorates in aging and especially in Alzheimer's disease (AD). It has remained unsettled, however, whether MMN is regulated by the cholinergic system, which is deteriorated in AD contributing to cognitive impairments. We recorded cortical auditory responses with a magnetometer from 13 healthy subjects after intravenous injection of scopolamine, centrally acting cholinergic antagonist, or glycopyrrolate, a drug with a peripheral anticholinergic properties without penetrating the blood-brain barrier, using a double-blind protocol. Scopolamine reduced MMNm amplitude in response to frequency, but not duration, change, increased P50m amplitude, and delayed N100m latency. These findings suggest that the cholinergic system regulates the frequency-specific comparison of incoming stimuli to existing memory trace and modulates the preattentive processing related to stimulus detection. Further, neural mechanisms responsible for cortical frequency- and duration-specific discrimination appear to have different sensitivities to cholinergic modulation. Auditory evoked potentials might be suitable to monitor cholinergic activity in AD.

Adult↗
PubMed2001

Effects of haloperidol on selective attention: a combined whole-head MEG and high-resolution EEG study.

We used 122-channel magnetoencephalography (MEG) and 64-channel electroencephalogrphy (EEG) simultaneously to study the effects of dopaminergic transmission on human selective attention in a randomized, double-blind placebo-controlled cross-over design. A single dose of dopamine D2 receptor antagonist haloperidol (2 mg) or placebo was given orally to 12 right-handed healthy volunteers 3 hours before measurement. In a dichotic selective attention task, subjects were presented with two trains of standard (700 Hz to the left ear, 1,100 Hz to the right ear) and deviant (770 and 1,210 Hz, respectively) tones. Subjects were instructed to count the tones presented to one ear; whereas, the tones presented to the other ear were to be ignored. Haloperidol significantly attenuated processing negativity (PN), an event-related potential (ERP) component elicited by selectively attended standard tones at 300-500 ms after stimulus presentation. These results, indicating impaired selective attention by a blockade of dopamine D2 receptors, were further accompanied with increased mismatch negativity (MMN), elicited by involuntary detection of task-irrelevant deviants. Taken together, haloperidol seemed to induce functional changes in neural networks accounting for both selective and involuntary attention, suggesting modulation of these functions by dopamine D2 receptors.

Acoustic Stimulation↗
PubMed2001

Northern epilepsy syndrome (NES, CLN8)--MRI and electrophysiological studies.

Northern epilepsy syndrome (NES, EPMR, progressive epilepsy with mental retardation, CLN8), an inherited childhood-onset epilepsy with mental retardation, has been recently characterized to belong to the family of neuronal ceroid lipofuscinoses (NCLs). In this study, four patients (ages 26-44 years) with NES and eight healthy controls underwent magnetic resonance imaging (MRI) and electrophysiological evaluation with somatosensory evoked magnetic field (SEF) studies. The findings in NES were compared with the known findings in juvenile NCL (JNCL, CLN3) and Finnish variant late infantile NCL (vLINCLFIN, CLN5) that manifest around the same age as NES. Also postmortem MRI was performed on one brain. On the MRIs, slight to moderate cerebellar atrophy was seen in all patients, whereas only two patients had slightly enlarged cerebral sulci. None of the MRIs demonstrated signal intensity abnormalities that are commonly seen in JNCL and vLINCLFIN and are considered to reflect the Wallerian degeneration after neuronal death. Generally SEFs in NES were within normal limits, indicating that the disease had not impaired the function of the neurons on the somatosensory pathway. In conclusion, MRI imaging and SEF findings suggest that the cerebral neuronal death and dysfunction in NES are minimal compared with JNCL and vLINCLFIN.

Adult↗
PubMed2000

Dynamics of mu-rhythm suppression caused by median nerve stimulation: a magnetoencephalographic study in human subjects.

We studied event-related desynchronization (ERD) of the 8-13 Hz rhythm (mu rhythm) of the primary somatosensory cortex (SI) caused by contra- and ipsilateral median-nerve stimulation. We used whole-head magnetoencephalography (MEG) and wavelet analysis together with our newly developed color-coded single-trial ERD display. The somatosensory stimuli suppressed mu rhythm at both contra- and ipsilateral SI, but the attenuation was clearly lateralized, being at least 20% stronger contra- than ipsilaterally. Moreover, repeated stimulation significantly reduced mu-rhythm ERD in the ipsilateral but not in the contralateral hemisphere in the course of the experiment. The observed lateralization is in agreement with the classical concept of a dominant role of the contralateral hemisphere in the processing of somatosensory information. The strong ipsilateral ERD in the beginning of the experiment may reflect the presence of non-specific arousal-like activation, which attenuates toward the end of the experiment.

Adult↗
PubMed2000

Suppression of transient 40-Hz auditory response by haloperidol suggests modulation of human selective attention by dopamine D2 receptors.

Cognitive processes including selective attention may depend on synchronous activity of neurons at the gamma-band (around 40Hz). To determine the effect of neuroleptic challenge on transient auditory evoked 40-Hz response, simultaneous measurement of 122-channel magnetoencephalogram (MEG) and 64-channel electroencephalogram (EEG) was used. Either 2mg of dopamine D(2)-receptor antagonist haloperidol or a placebo was administered orally to 11healthy subjects in a double-blind randomized crossover design in two separate sessions. The subjects attended to tones presented to one ear and ignored those presented to the other ear. Haloperidol significantly suppressed the transient 40-Hz electric response to the attended stimuli, while no significant effect was observed in the electric responses to the unattended tones or in the magnetic responses. The present result suggests that dopamine D(2) receptors modulate selective attention.

Acoustic Stimulation↗
PubMed2000

Somatosensory evoked magnetic fields: relation to pre-stimulus mu rhythm.

OBJECTIVES: Brain responses to auditory and visual stimuli have been previously shown to depend on the level of spontaneous brain activity in the 8-13 Hz range. Our aim was to determine whether somatosensory evoked responses are influenced by ongoing rhythmic activity in the 8-13 Hz frequency range originating in the sensorimotor cortex (mu rhythm). METHODS: We used a whole-head 122 channel magnetoencephalography (MEG) system to record somatosensory evoked fields (SEFs) in response to median nerve stimulation in 11 subjects. Spontaneous oscillations in the 8-13 Hz band over the contralateral sensorimotor cortex were evaluated in 3 different pre-stimulus time intervals using wavelet analysis. RESULTS: The N20m SEF deflection did not depend on pre-stimulus activity, while the amplitude of the P35m deflection, and to a lesser extent that of the P60m deflection, showed a small positive correlation with the amplitude of the pre-stimulus mu rhythm. Although the amplitude of the mu rhythm varied by a factor of 2.3-5, the maximum variations in P35m and P60m amplitude were only 21 and 12%, respectively. The latencies of the peaks were not affected by the strength of the pre-stimulus mu rhythm. CONCLUSIONS: It appears that the first excitatory cortical response (N20m) is independent of the oscillatory state (8-13 Hz frequency range) of the sensorimotor cortex. Later parts of the response (P35m and P60m) are also relatively stable compared with the large variations in mu rhythm.

Adult↗
PubMed2000

Specific changes in somatosensory evoked magnetic fields during recovery from sensorimotor stroke.

We studied recovery-induced changes in the responsiveness of the primary somatosensory cortex in stroke patients with sensory and/or motor symptoms. Somatosensory evoked magnetic fields, in response to median nerve stimulation, were recorded in 14 patients with their first symptomatic unilateral stroke 1 to 15 days from the first symptoms and again 2 to 3 months later. Neuronal activity at the contralateral primary somatosensory cortex was modeled with equivalent current dipoles at the peak latencies of the first two cortical deflections at about 20 msec (N1m) and at 28 to 91 msec (P1m). Twenty-three age-matched healthy volunteers, 9 of whom were tested also in serial recordings, served as control subjects. At follow-up, 6 patients showed a significant increase of P1m amplitude, whereas N1m increased only in 1. Clinical improvement of two-point discrimination ability, but not of other basic somatosensory skills, was significantly correlated with the increase of P1m. We conclude that the recovery of discriminative touch after stroke is paralleled by the growth of the P1m somatosensory evoked magnetic field deflection, and we propose that this may reflect re-establishment of lateral inhibitory functions at the primary somatosensory cortex.

Adult↗