Biomedical subjects

J Karhu

Publications and source records attributed to J Karhu.

At least 19 recordsLinked to original sources

PubMed2001

Effects of maternity on auditory event-related potentials to human sound.

Auditory event-related brain potentials (ERPs) were recorded in response to an emotional (a baby's cry) and a neutral (a word) stimulus in a group of mothers 2-5 days after childbirth (n = 20) and in control women (n = 18) who were not in the state of early motherhood. For each mother, her own infant's cry was recorded and used as the cry stimulus, whereas a strange baby's cry was used for control women. The word stimulus was identical for both groups. Stimuli were presented in intermittent trains in order to study the arousal responses to the first stimuli of the trains, and refractoriness of ERPs during stimulus repetition. The N100 responses were significantly larger in amplitude in mothers than in control women, not only to the emotional cry stimuli but also to the neutral word stimuli. The finding suggests a general increase in alertness and arousal in mothers, which may be necessary in enabling the mother to be continuously alert to her infant's needs. This allows good care of the infant and may be essential in building an emotional tie between the mother and her child.

Acoustic Stimulation↗

PubMed2001

Auditory event-related potentials differentiate patients with normal pressure hydrocephalus and patients with concomitant Alzheimer's disease verified by brain biopsy.

We studied 51 patients with clinical symptoms and CT findings suggesting normal pressure hydrocephalus (NPH). Tests included head MRI, auditory event-related potentials (ERPs), thorough neuropsychological testing and intraventricular intracranial 24 h pressure recording and infusion testing. A brain biopsy was also obtained to verify a concomitant dementing process (Alzheimer's disease; AD). Patients were divided into subgroups according to the need of shunt and the biopsy findings, and their ERPs were analysed blindly. The present results suggest that non-invasive ERPs aid in the differentiation of pure NPH from NPH with concomitant AD.

Aged↗

PubMed2001

Ethanol modulates cortical activity: direct evidence with combined TMS and EEG.

The motor cortex of 10 healthy subjects was stimulated by transcranial magnetic stimulation (TMS) before and after ethanol challenge (0.8 g/kg resulting in blood concentration of 0.77 +/- 0.14 ml/liter). The electrical brain activity resulting from the brief electromagnetic pulse was recorded with high-resolution electroencephalography (EEG) and located using inversion algorithms. Focal magnetic pulses to the left motor cortex were delivered with a figure-of-eight coil at the random interstimulus interval of 1.5-2.5 s. The stimulation intensity was adjusted to the motor threshold of abductor digiti minimi. Two conditions before and after ethanol ingestion (30 min) were applied: (1) real TMS, with the coil pressed against the scalp; and (2) control condition, with the coil separated from the scalp by a 2-cm-thick piece of plastic. A separate EMG control recording of one subject during TMS was made with two bipolar platinum needle electrodes inserted to the left temporal muscle. In each condition, 120 pulses were delivered. The EEG was recorded from 60 scalp electrodes. A peak in the EEG signals was observed at 43 ms after the TMS pulse in the real-TMS condition but not in the control condition or in the control scalp EMG. Potential maps before and after ethanol ingestion were significantly different from each other (P = 0.01), but no differences were found in the control condition. Ethanol changed the TMS-evoked potentials over right frontal and left parietal areas, the underlying effect appearing to be largest in the right prefrontal area. Our findings suggest that ethanol may have changed the functional connectivity between prefrontal and motor cortices. This new noninvasive method provides direct evidence about the modulation of cortical connectivity after ethanol challenge.

Adult↗

PubMed2001

Reduced serotonin transporter binding in binge eating women.

RATIONALE: There is evidence that abnormalities in brain dopamine, norepinephrine and serotonin metabolism may play an important role in binge eating. Serotonin-active antidepressant drugs have also been found to decrease binge eating. OBJECTIVE: We investigated serotonin transporter binding in obese binge-eating women. Eleven obese binge-eating and seven obese control women participated in the study. The subjects were not taking any medication known to affect serotonin (5-HT) transporters. METHODS: We used single-photon emission tomography (SPECT) with the radioligand 123I-labelled nor-beta-CIT, which specifically labels 5-HT transporters. RESULTS: Obese binge-eating women showed significantly decreased 5-HT transporter binding in the mid-brain compared with obese controls (2.1 +/- 0.5 versus 2.9 +/- 0.5, respectively). CONCLUSIONS: SPECT imaging with a ligand specific for 5-HT transporters can be used to assess altered serotonin transporter binding in the living human brain. The results tentatively suggest that 5-HT transporter binding is decreased in binge-eating women.

Adult↗

PubMed2001

Dynamic behavior of the auditory N100 elicited by a baby's cry.

We compared auditory N100 responses in female adults to two non-attended human sound stimuli. An infant's cry represented an unfamiliar, emotionally colored sound and the Finnish word "hei" (meaning "hi") a familiar and emotionally neutral sound. Both sounds elicited clear N100 responses over auditory areas in both hemispheres. However, the dynamic behavior of the N100 response following the first few repetitions of the sounds was significantly different. We observed faster habituation and longer response latencies, particularly over the ipsilateral hemisphere, during the first and second repetitions of the cry stimulus. This pattern may reflect an altered arousal level and slower, bilateral processing during the unfamiliar emotionally loaded cry as compared to the emotionally neutral word "hei" .

Acoustics↗

PubMed2001

Loss of time-organized sympathetic skin responses in acute psychosis.

The aim of this study was to differentiate the response pattern characteristics of sympathetic skin responses (SSR) between unmedicated first psychotic subjects and healthy controls. We recorded SSR to novel auditory stimuli in 13 psychotic subjects and in 19 controls. There was no constant delay between a sudden change in the acoustic surroundings and SSR in psychotic subjects, whereas regularly this delay was 1.3 to 1.8 seconds in controls. The validity of the test was evaluated by blind rating responses to two categories. The lack of a regular time delay between a novel auditory stimulus and SSR suggests a timing disturbance in the neural networks regulating the autonomic nervous system responses in acute psychosis. Our finding and method may have future implications in evaluation of subtle autonomic nervous system alterations related, e.g., to drug effects.

Acoustic Stimulation↗

PubMed2001

Transcranial magnetic stimulation as a tool for cognitive studies.

Transcranial Magnetic Stimulation (TMS) is a tool for the non-invasive stimulation of the human brain. It allows the activation of arbitrary sites of the superficial cortex and, combined with other brain-imaging techniques such as EEG, PET, and fMRI, it can be used to evaluate cortical excitability and connectivity. This is of major importance in, for example, the study of cognitive processes such as language, learning, memory and self-representation, which are thought to be represented in multiple brain areas. The mechanisms of action of TMS are known on a basic level, but its effect on the activation state of brain tissue is still poorly understood. Clinical applications of TMS have also been proposed and guidelines for its safe use drafted.

Brain↗

PubMed2000

Theta oscillations index human hippocampal activation during a working memory task.

Working memory (WM) is the ability to retain and associate information over brief time intervals. Functional imaging studies demonstrate that WM is mediated by a distributed network including frontal and posterior cortices, hippocampus, and cerebellum. In rodents, the presentation of stimuli in a WM task is followed by a reset of the phase of hippocampal theta. In this paper we report the observation of a similar phenomenon in normal human subjects. Neuromagnetic responses were recorded during presentation of a set of digits and a subsequent probe of the retained items. All stimuli were presented with a fixed temporal pattern. We observed phase reset of approximately 7 Hz theta in left hippocampus approximately 120 ms after probe stimuli, whereas reset of theta in right hippocampus was visible approximately 80 ms prior to these anticipated stimuli. The duration of stimulus-locked theta increased with memory load, with a limiting value of approximately 600 ms for 5-7 retained items. We suggest that, as in rats, stimulus-locked theta may index involvement of human hippocampal networks in the cognitive processing of sensory input. The anticipatory phase reset of theta indicates involvement of hippocampus in right hemisphere and cerebellar timing networks. Hippocampal structures are essential for orientation to perturbations in the sensory scene, a function that requires use of a context established by a constellation of stimuli. We suggest that the initiation and maintenance of stimulus-locked hippocampal theta observed here may facilitate processing of potentially salient and/or novel input with respect to a context established by the contents of WM.

Adult↗

PubMed2000

IBIS data library: clinical description of the Finnish database. Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery.

Improved monitoring of brain function in intensive care and surgery is a project aiming to develop methods of biosignal processing and interpretation, in order to characterise critical events during anaesthesia and cardiac surgery, effect of anaesthesia regimen, neurophysiological findings of different sedation levels, arousal from post-anaesthesia sedation, post-cardiopulmonary bypass brain dysfunction and early brain dysfunction in patients with multiple organ failure. A data library was collected in the three participating hospitals. This is a description of the data library from the University Hospital of Kuopio, Finland, which includes data from 40 patients after cardiac surgery and from seven patients with multiple organ dysfunction. This project demonstrates that active neuromonitoring can be performed in the intensive care unit without interference with the normal treatment and care. The presented database may serve other scientific workers as a reference for a typical spectrum of perioperative data with respect to severity of disease, length of cardiopulmonary bypass, postoperative levels of sedation and length of hospital stay in cardiac surgery patients, and for types of diseases and outcome in patients with multiple organ dysfunction.

Adult↗

PubMed2000

Quantification of haemodynamic response to auditory stimulus in intensive care.

Measuring effects of sensory stimuli on haemodynamics could provide information about the interplay between central and autonomous nervous system (ANS). However, ANS response to sensory stimulus has received little attention. In this paper we present a signal processing scheme to extract the responses of heart rate and systemic arterial pressure on auditory stimulus in intensive care patients (N=5). In short, the effect of mechanical ventilation is rejected by optimal linear modelling. Other disturbances are attenuated by filtering and efficient rejection of outlying sweeps of data. The results show identifiable responses on three out of five cases. The response characteristics may be explained by synchronisation of spontaneous variability in systemic arterial pressure to auditory stimulus.

Acoustic Stimulation↗

PubMed2000

Single sweep analysis of event related auditory potentials for the monitoring of sedation in cardiac surgery patients.

Event-related potentials (ERPs) from the auditory system were investigated in 28 post-operative cardiac patients in order to assess their relevance in the monitoring of patient sedation level. Midazolam (17 patients) and propofol (11 patients) were the sedative agents used. The auditory ERP components of N100 (HAB100) and mismatch negativity (MMN) were considered. A single sweep method based on the AutoRegressive with eXogenous input (ARX) model, which is able to enhance the evoked responses to each single stimulus, was used to process each sweep and to compute traditional parameters on a sweep-by-sweep basis. Differences in the measured parameters were related to variations in the patient sedation levels classified through Ramsay score. Significant differences (P<0.05) in both MMN and HAB100 parameters were found between light sedation (LS) and deep sedation (DS) levels.

Aged↗

PubMed1999

Reduced mismatch negativity (MMN) suggests deficits in pre-attentive auditory processing in distractible children.

Mismatch negativity (MMN) event-related brain potential reflects the brain's automatic auditory change detection mechanism that depends on integrity of the auditory sensory memory. We studied MMN in easily distractible (n = 20) and in non-distractible (n = 20) healthy 9-year-old children. Two MMN phases were revealed in both groups: an earlier MMN peak at approximately 220 ms and a later negative slope approximately 300-500 ms after stimulus presentation. The results suggested a strong frontal lobe contribution in the generation of the later MMN phase, and this response was significantly reduced in amplitude in the distractible children. The present findings suggest that distractible children may have deficits in the frontally mediated aspects of auditory sensory memory.

Attention Deficit Disorder with Hyperactivity↗

PubMed1999

Persistent frontal P300 brain potential suggests abnormal processing of auditory information in distractible children.

The P300 event-related potential (ERP) was studied at the beginning, in the middle, and at the end of an auditory stimulus discrimination task in 70 normal 9-year-old children. Easily distractible children showed frontally a short-latency P300 response to target stimuli throughout the task, whereas in the non-distractible children the corresponding response was distinctly smaller and also showed a tendency to decrease in size towards the end of the task. The short-latency frontal P300 response reflects activation of the brain's orienting networks, and it normally decreases in size when stimuli lose their 'novelty value' with stimulus repetition. Persistent frontal P300 suggest that distractible children continued to show enhanced orienting to stimuli that should have already been well encoded and/or categorized.

Acoustic Stimulation↗

PubMed1999

What does the P300 brain response measure in children? New insight from stimulus sequence studies.

The decrease in the P300 brain response latency with increasing age is often taken to reflect maturation of cognitive processes in children. We found that in abnormally distractible children the auditory P300 latency decreased significantly when the inter-target interval (ITI) increased in a stimulus discrimination task. We speculate that the sensory memory trace of the target stimulus may decay in distractible children during longer ITIs, and consequently the next target stimulus may activate the brain's orienting networks that are known to generate shorter latency brain responses. The relative strength by which the functionally different neural networks underlying the cognitive brain responses are activated may contribute significantly to the latency measures of these responses. The presumption that a short P300 latency equals to fast processing may thus be over-simplistic, especially in children.

Acoustic Stimulation↗

PubMed1999

Distractible children show abnormal orienting to non-attended auditory stimuli.

Event-related potentials were recorded in response to intermittently presented, non-attended trains of identical auditory stimuli in healthy 9-year-old children. In abnormally distractible children (n =24), the first tone in each train elicited a significantly larger N1 vertex response than in the non-distractible children (n 24), suggesting that increased distractibility may be associated with an abnormally strong cerebral orienting towards non-attended stimuli. A later negativity at around 300 ms, which increases in amplitude with stimulus repetition and may thus reflect the building up of a functional neuronal representation of the stimulus properties, was significantly smaller in the distractible than in the non-distractible children. These findings demonstrate that event-related potential measures may be useful in helping to understand the information processing found in distractible children.

Acoustic Stimulation↗

PubMed1999

Dopamine transporter and D2-receptor density in late-onset alcoholism.

RATIONALE: Late onset type 1 alcoholism has been suggested to be associated with an underlying dopaminergic defect. Therefore, it is relevant to study both postsynaptic D2-receptor and presynaptic dopamine transporter (DAT) densities among alcoholics. OBJECTIVE: We investigated DAT densities, along with striatal and extrastriatal dopamine D2-receptor densities, in nine nonviolent late-onset male alcoholics, who had no major mental disorder nor antisocial personality disorder (ASPD), and nine healthy controls. METHODS: [123I]PE2I and [123I]epidepride were used in SPECT imaging. RESULTS: DAT occupancy ratios (striatum/cerebellum) were significantly lower among alcoholics than in controls. Extrastriatal D2-receptor occupancy ratios (temporal pole/cerebellum) were not significantly different between the groups. CONCLUSIONS: Striatal presynaptic DAT densities are decreased among type 1 alcoholics, and this finding is not associated with recent alcohol abuse.

Adult↗

PubMed1999

P300 sequence effects differ between children and adults for auditory stimuli.

Variation of the P300 component was studied in normal children and adults during an auditory oddball paradigm. In children, the target stimuli that were preceded by a large number of standard stimuli elicited about twice as large P300 with a significantly shorter latency, a more widespread distribution, and an earlier positivity in the frontal area than those that were preceded by a small number of standard stimuli. The P300 variation was not as marked in adults as in children. Based on the context updating theory of the P300, the finding suggests that a long intertarget interval (ITI) results in a profound decay of the neural representation of the target stimulus in children; consequently, more resources are needed to update the neural representation, and the target may even be processed as a novel input. The P300 variation may provide information about the brain functions related to memory, attention, and orienting in children. This variation should be considered when assessing cognitive brain functions with event-related potentials in children.

Adult↗

PubMed1999

Altered parallel auditory processing in schizophrenia patients.

Patients with schizophrenia have impaired auditory processing that has been demonstrated by diminished P50 response to paired auditory stimuli in event-related potential (ERP) studies. Cerebral processing can also be studied with magnetoencephalography (MEG). With a whole-head MEG, which enables one to simultaneously measure brain activity in both hemispheres, we investigated whether early parallel auditory processing is impaired in schizophrenia. Sequences of tones were monaurally presented to schizophrenia patients and healthy controls in a passive condition, and the event-related magnetic fields were recorded simultaneously over both auditory cortices. The interhemispheric latency difference of the P50m, but not that of the N100m, was significantly shorter in the patient group in the right-ear but not in the left-ear stimulus condition. Further, the ipsilateral P50m was significantly earlier in schizophrenia patients in the right-ear condition. This result suggests that schizophrenia affects the consecutive preconscious auditory processing in a different manner.

Adult↗