Biomedical subjects

Seppo Kähkönen

Publications and source records attributed to Seppo Kähkönen.

At least 19 recordsLinked to original sources

PubMed2007

Impaired functional connectivity at EEG alpha and theta frequency bands in major depression.

Recent reports on functional brain imaging in major depression have lead to an assumption that observed psychopathology might be related to an altered brain functional connectivity. Our hypothesis was that an increase in brain functional connectivity occurs in major depression. As a measure of functional connectivity, the electroencephalogram (EEG) structural synchrony approach was used in 12 medication-free depressive outpatients and 10 control subjects. Differences in the number and strength of structurally synchronized EEG patterns were compared between groups. In depressive patients the number and strength of short cortex functional connections were significantly larger for the left than for the right hemisphere, while the number and strength of long functional connections were significantly larger for the right than for the left hemisphere. Some of the functional connections were positively correlated with the severity of depression, thus being predictive. These were short-range anterior, posterior, and left hemisphere functional connections for the alpha frequency band and short-range anterior functional connections for the theta frequency band. The topology of the most representative functional connections among all patients with major depression indicated that the right anterior and left posterior brain parts may discriminate depressive patients from healthy controls. The obtained data support our hypothesis that there is an increase in brain functional connectivity in major depression. This finding was interpreted within the semantic framework, where different specialization of left (monosemantic context) and right (polysemantic context) hemispheres is functionally insufficient in patients with depression.

Adult↗

PubMed2006

Reorganization of the composition of brain oscillations and their temporal characteristics in opioid dependent patients.

In the present study, we examined the composition of electroencephalographic (EEG) brain oscillations in broad frequency band (0.5-30 Hz) in 22 opioid-dependent patients and 14 healthy subjects during resting condition (closed eyes). The exact compositions of brain oscillations and their temporal behavior were assessed by the probability-classification analysis of short-term EEG spectral patterns. It was demonstrated that EEG of patients with opioid dependence was characterized by (a) significant reorganization of brain oscillations with increase in the percentage of beta- and mostly fast-alpha-rhythmic segments, (b) longer periods of temporal stabilization for alpha and beta brain oscillations and by shorter periods of temporal stabilization for theta and polyrhythmic activity when compared with control subjects, and (c) right-sided dominance (significantly larger relative presence of particular spectral patterns in EEG channels of the right hemisphere). These effects were widely distributed across the cortex with the maximum magnitude in the occipital, right parietal, temporal, and frontal areas. Taken together the present study suggested (a) an allostatic state with neuronal activation, and (b) high sensitivity of the right hemisphere to adverse opioid effects.

Adult↗

PubMed2006

Composition of brain oscillations in ongoing EEG during major depression disorder.

In the present study, we examined the composition of electroencephalographic (EEG) brain oscillations in 12 unmedicated major depressive outpatients and 10 healthy subjects during resting conditions (closed eyes). The exact composition of brain oscillations was assessed by the probability-classification analysis of short-term EEG spectral patterns. In contrast to previous studies of depression, the current study found that major depression affects brain activity in nearly the whole cortex and manifests itself in considerable reorganization of the composition of brain oscillations in a broad frequency range: 0.5-30 Hz. At the same time, the magnitude of the effect of depression was maximal in the posterior cortex of the brain. Interhemisphere asymmetry during major depression was also observed in the whole cortex with right hyperactivity in frontal, parietal and occipital brain areas. It is suggested that depressive brain is manifested in the superposition of distributed multiple oscillations. Our findings provide new insight on the relationship between major depressive disorder and cortical oscillatory activity.

Adult↗

PubMed2006

Increased local and decreased remote functional connectivity at EEG alpha and beta frequency bands in opioid-dependent patients.

RATIONALE: Although researchers now have a working knowledge of key brain structures involved in realization of actions of substance abuse and addiction, deeper understanding will require examination of network interactions between cortical neuronal assemblies and their subcortical tails in the effects of opioid dependence. OBJECTIVES: Given that repeated exposure to opiates initiates a widespread reorganization of cortical regions, we predict that opioid dependence would result in a considerable reorganization of local and remote functional connectivity in the neocortex. METHODS: We applied the novel operational architectonics approach that enables us to estimate two local and remote functional cortex connectivities by means of electroencephalogram structural synchrony measure. RESULTS: In 22 opioid-dependent patients, we found the evidence that brain functional connectivity was indeed disrupted by chronic opioid abuse (i.e., the local functional connectivity increased and remote functional connectivity decreased in opioid abusers). This significant difference between "opioid" and "control" populations was the same for alpha and beta frequency bands. Additionally, significant negative relations between duration (years) of daily opioid abuse and the number/strength of functional connections in the posterior section of the cortex were found.

Adult↗

PubMed2006

The novelty value of the combined use of electroencephalography and transcranial magnetic stimulation for neuroscience research.

Electroencephalographic (EEG) responses measured simultaneously with transcranial magnetic stimulation (TMS) have opened a new window into the human nervous system. The combined use of TMS and EEG (TMS-EEG) provides a means for the detailed study of the reactivity of any cortical region in the intact brain; also the reactivities of non-motor cortical areas related with higher-order functions are now appreciable. A recent epochal finding concerning cortical reactivity is that neuronal activation is induced with remarkably low stimulation intensities. This knowledge is significant when optimizing experimental set-ups for maximal patient safety. Stimulation of different cortical areas evokes different patterns of remote EEG activity, confirming the viability of TMS-EEG for the study of corticocortical connections. In this review, we expand on these and other notable findings related with TMS-EEG. We discuss the possibilities of the technique for the study of cortical reactivity and connectivity. We show that TMS-EEG allows the study of interhemispheric connections with high spatiotemporal specificity and the assessment of cortical reactivity with excellent sensitivity.

Biomedical Research↗

PubMed2006

Cognitive function during early abstinence from opioid dependence: a comparison to age, gender, and verbal intelligence matched controls.

BACKGROUND: Individuals with opioid dependence have cognitive deficits during abuse period in attention, working memory, episodic memory, and executive function. After protracted abstinence consistent cognitive deficit has been found only in executive function. However, few studies have explored cognitive function during first weeks of abstinence. The purpose of this study was to study cognitive function of individuals with opioid dependence during early abstinence. It was hypothesized that cognitive deficits are pronounced immediately after peak withdrawal symptoms have passed and then partially recover. METHODS: Fifteen patients with opioid dependence and fifteen controls matched for, age, gender, and verbal intelligence were tested with a cognitive test battery When patients performed worse than controls correlations between cognitive performance and days of withdrawal, duration of opioid abuse, duration of any substance abuse, or opioid withdrawal symptom inventory score (Short Opiate Withdrawal Scale) were analyzed. RESULTS: Early abstinent opioid dependent patients performed statistically significantly worse than controls in tests measuring complex working memory, executive function, and fluid intelligence. Their complex working memory and fluid intelligence performances correlated statistically significantly with days of withdrawal. CONCLUSION: The results indicate a rather general neurocognitive deficit in higher order cognition. It is suggested that cognitive deficit during early abstinence from opioid dependence is related to withdrawal induced neural dysregulation in the prefrontal cortex and is partly transient.

Adult↗

PubMed2006

Effects of risperidone on auditory information processing in neuroleptic-naive patients with schizophrenia spectrum disorders.

Early effects of risperidone (2.5 +/- 1 mg/day) on auditory information processing were investigated in 9 neuroleptic naive patients with schizophrenia spectrum disorders and 9 healthy controls by using event-related potentials (ERPs). ERPs were elicited during active auditory "oddball" paradigm and were recorded before and after two weeks of treatment. Baseline P3 latencies were significantly delayed in patient group. Risperidone treatment did not change P3 amplitudes and latencies. However, P2 amplitudes were reduced in parallel with the clinical improvement measured by Positive and Negative Syndrome Scale (PANSS). Although risperidone did not change neural bases of active attention after two weeks of treatment, the reduction of P2 amplitude suggests that risperidone may affect auditory information processing in patients with schizophrenia spectrum disorders who never have been exposed to antipsychotic treatment.

Adolescent↗

PubMed2006

[Not Available].

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Journal Article↗

PubMed2005

Breakdown of long-range temporal correlations in theta oscillations in patients with major depressive disorder.

Neuroimaging has revealed robust large-scale patterns of high neuronal activity in the human brain in the classical eyes-closed wakeful rest condition, pointing to the presence of a baseline of sustained endogenous processing in the absence of stimulus-driven neuronal activity. This baseline state has been shown to differ in major depressive disorder. More recently, several studies have documented that despite having a complex temporal structure, baseline oscillatory activity is characterized by persistent autocorrelations for tens of seconds that are highly replicable within and across subjects. The functional significance of these long-range temporal correlations has remained unknown. We recorded neuromagnetic activity in patients with a major depressive disorder and in healthy control subjects during eyes-closed wakeful rest and quantified the long-range temporal correlations in the amplitude fluctuations of different frequency bands. We found that temporal correlations in the theta-frequency band (3-7 Hz) were almost absent in the 5-100 s time range in the patients but prominent in the control subjects. The magnitude of temporal correlations over the left temporocentral region predicted the severity of depression in the patients. These data indicate that long-range temporal correlations in theta oscillations are a salient characteristic of the healthy human brain and may have diagnostic potential in psychiatric disorders. We propose a link between the abnormal temporal structure of theta oscillations in the depressive patients and the systems-level impairments of limbic-cortical networks that have been identified in recent anatomical and functional studies of patients with major depressive disorder.

Adult↗

PubMed2005

Responses to cardiovascular drugs during alcohol withdrawal.

AIM: To present findings on the kinetics and dynamics of cardiovascular drugs during alcohol withdrawal (AW), compared with that observed in remission. METHOD: Studies were reviewed and summarized. RESULTS: A single-dose study in alcoholic patients with propranolol, a beta-adrenergic antagonist, showed that the negative inotropic effect was decreased and the bradycardiac effect increased during AW as compared with during early remission. The hypotensive effect of isosorbid dinitrate, commonly used as a vasodilatator, was weaker at the onset of AW, being associated with the decreased bioavailability of the drug. Verapamil, which is a L-type Ca2+ channel antagonist, produced a bradycardiac effect at the onset of AW, but no effect was observed in early remission. The effect was probably due to changes in L-type Ca2+ channels because no differences in verapamil concentrations between AW and early remission were observed. CONCLUSION: Taken together, AW modifies the dynamics and kinetics of cardiac drugs, which may have an impact on the treatment of alcoholic patients with cardiac diseases.

Adrenergic beta-Antagonists↗

PubMed2005

Prefrontal TMS produces smaller EEG responses than motor-cortex TMS: implications for rTMS treatment in depression.

RATIONALE: The stimulus intensity of prefrontal repetitive transcranial magnetic stimulation (rTMS) during depression treatment is usually determined by adjusting it with respect to the motor threshold (MT). There is some evidence that reactivity of the prefrontal cortex to transcranial magnetic stimulation (TMS) is lower than that of the motor cortex at MT stimulation. However, it is unknown whether this is true when other stimulus intensities are used. We investigated whether the magnitude and shape of the overall TMS-evoked electroencephalographic (EEG) responses differ between prefrontal and motor cortices. METHODS: Magnetic pulses to the left motor and prefrontal cortices (the middle frontal gyrus identified from magnetic resonance images) were delivered at four intensities (60, 80, 100, and 120% of MT of the right abductor digiti minimi muscle) for six subjects. Simultaneously, EEG was recorded with 60 scalp electrodes. RESULTS: Global mean-field amplitudes (GMFAs) reflecting overall cortical activity were significantly smaller after prefrontal- than after motor-cortex TMS. A significant positive correlation (r (s)=0.84, p<0.01) was found between GMFAs of motor- and prefrontal-cortex TMS across the experiments. However, when correlation between the responses of motor and prefrontal cortices was examined, significant positive correlations were found at 80 and 100% intensities only. CONCLUSIONS: This study provides further evidence that the prefrontal and motor cortices have different reactivity to TMS, but the MT may be used for determining the stimulus intensity of prefrontal rTMS treatment in depression, at least at motor threshold intensities or near to it.

Adult↗

PubMed2005

Magnetoencephalography (MEG): a non-invasive tool for studying cortical effects in psychopharmacology.

Magnetoencephalography (MEG) is a non-invasive method for studying magnetic fields generated by simultaneously firing neurons outside the skull. The skull, scalp and brain tissue do not distort magnetic fields, so the cortical activity can be easily measured. MEG is starting to be used to explore the effects of various psychopharmacological agents on resting brain, sensory and cognitive processing. Scopolamine and agents enhancing GABA functions have shown differential effects on cortical neural oscillations. Further, with GABA, serotonin, dopamine and acetylcholine transmissions have differential effects on early cortical and pre-attentional processing in the auditory and frontal cortices. Monoamines also differently regulate the activity of the somatosensory cortex. Taken together, MEG with a resolution of milliseconds allows exploration of focal cortical effects of psychopharmacological agents giving information different from other brain-imaging modalities.

Brain Mapping↗

PubMed2005

Serotonergic modulation of mismatch negativity.

Neurochemical mechanisms mediating the interaction between emotional and cognitive processing are not yet fully understood. Here, we utilized acute tryptophan depletion (ATD) to reduce the brain synthesis of serotonin (5-HT), which is thought to have a central role in regulation of emotions and mood in humans. ATD effects on event-related potentials and magnetic fields were studied using a passive odd-ball paradigm in a randomized, double-blinded, controlled, cross-over design. Auditory responses were recorded simultaneously with high-resolution magnetoencephalography (MEG) and electroencephalography (EEG) in 14 healthy subjects, 5 h after ATD or a control condition. ATD significantly increased depressed mood and lowered plasma tryptophan concentration (total tryptophan decreased by 75%, free tryptophan decreased by 39%). As compared with the control condition, ATD increased the amplitudes of mismatch negativity (MMN) to duration and frequency changes and decreased the latencies of magnetic MMN to frequency changes in the hemisphere ipsilateral to the ear stimulated. Further, ATD modulated N1m latencies and decreased P2m source activity. ATD increased the interhemispheric latency difference of MMNm to frequency changes. No effects on P50 were observed. The present results suggest serotonergic modulation of preattentive auditory change detection, suggested to initiate involuntary attention shifting in the human brain.

Adult↗

PubMed2005

MEG and TMS combined with EEG for mapping alcohol effects.

Magnetoencephalography (MEG) is a noninvasive method of studying magnetic fields from outside the skull that are generated by at least partially synchronized neuronal populations in the brain. The advantage of MEG over electroencephalography (EEG) is the transparency of the skull, scalp, and brain tissue to the magnetic fields, which facilitates easy localization of the cortical activity. In MEG, alcohol increased the relative power of the alpha rhythm and reduced the relative power of beta activity in parieto-occipital regions. In contrast, no changes were observed in EEG, indicating that these methods differently detect alcohol's action on the cortex. Furthermore, MEG and EEG also differently detected the effects of alcohol on cognition. Alcohol reduced magnetic and electric auditory N1 and mismatch negativity amplitudes. P3a amplitudes were also reduced in EEG but not in MEG, suggesting that different cortical areas are responsible for alcohol's action on involuntary attention. Transcranial magnetic stimulation (TMS) provides new possibilities for studying localized changes in the electrical properties of the human cortex, especially when combined with EEG. Different cortical areas can be stimulated and the subsequent brain activity can be measured, yielding information about cortical excitability and connectivity. Alcohol modulates EEG responses evoked by motor-cortex TMS, the effects being largest at the right prefrontal cortex (assessed by minimum-norm estimation), meaning that alcohol changed the functional connectivity between motor and prefrontal cortices. Furthermore, alcohol decreases amplitudes of EEG responses after the left prefrontal stimulation of anterior parts of the cortex, which may be associated with the decrease of prefrontal cortical excitability. Taken together, MEG and TMS combined with EEG provide new insight into the focal actions of alcohol on the cortex with a temporal resolution of milliseconds, giving information different from that given by other brain imaging modalities.

Alcohol Drinking↗

PubMed2005

Functional connectivity in the brain--is it an elusive concept?

Even though functional brain connectivity is an influential concept in modern cognitive neuroscience, it is a very controversial notion. This is why further theoretical and methodological clarification are needed to help define precisely what is meant by functional connectivity and to help frame-associated issues. In this review we present the neurophysiological concept of functional connectivity, which utilizes in a plausible manner the notion of neural assemblies, as well as local and large-scale levels of description. Here functional connectivity is the mechanism for the coordination of activity between different neural assemblies in order to achieve a complex cognitive task or perceptual process. Our theoretical and empirical findings offer new insights into possible implications of the concept of functional connectivity for cognitive neuroscience.

Animals↗

PubMed2005

Effects of olanzapine on auditory P300 and mismatch negativity (MMN) in schizophrenia spectrum disorders.

We investigated effects of olanzapine (5-10 mg/day) on passive and active attention in 11 patients with schizophrenia spectrum disorders and 15 healthy controls by using auditory evoked potentials (AEPs) mismatch negativity (MMN) and P300. AEPs were elicited during active and passive auditory "oddball" paradigms before, after 2 weeks and 4 weeks of olanzapine treatment. Baseline P300 amplitudes, but not MMN, were significantly reduced in patients compared with controls. Although clinical signs improved significantly measured by Positive and Negative Syndrome Scale (PANSS), olanzapine had no significant effects on latencies and amplitudes of MMN and P300. Thus, olanzapine does not have effects on active and passive attention in patients with schizophrenia spectrum disorders. Four weeks olanzapine treatment may be insufficient for the improvement of cognitive dysfunction in terms of inability to focus on relevant stimuli in these patients.

Adolescent↗

PubMed2005

Effects of alcohol on spontaneous neuronal oscillations: a combined magnetoencephalography and electroencephalography study.

Electroencephalography (EEG) and magnetoencephalography (MEG) can detect different aspects of alcohol effects on auditory processing measured with event-related potentials and magnetic fields. The present study aimed to detect alcohol-induced changes in spontaneous neuronal oscillations with combined EEG and MEG techniques. The effects of alcohol on spontaneous neuronal rhythms were studied in 12 healthy subjects after 0.8 g/kg alcohol or juice in a double-blind, placebo-controlled, cross-over design using simultaneous high-resolution MEG and EEG in eyes-open and eyes-closed conditions. The data were analyzed with a power spectral density analysis. MEG recording showed that alcohol significantly increased the relative power of alpha rhythm (8-10 Hz) and reduced the relative power of beta activity (17-25 Hz) in both left and right hemispheres, but only in the eyes-closed condition. These effects did not depend on gender. No analogous statistically significant changes were observed in EEG rhythms. However, the power of alpha and beta rhythms was positively correlated in MEG and EEG recordings, indicating that MEG and EEG reflect similar processes. A distinct sensitivity of MEG and EEG to the sources of cortical oscillations, a better signal-to-noise ratio of MEG, as well as strong spatial blurring of potentials in EEG are most likely the reasons for the observed differences in the effects of alcohol on spontaneous oscillations as detected with two methods.

Adult↗

PubMed2005

Do individuals with former amphetamine dependence have cognitive deficits?

The association between former amphetamine dependence and cognitive performance was studied in a sample of 12 individuals with former amphetamine dependence who had been abstinent for at least 1 year and in 12 age-, gender- and verbal IQ-matched controls. The groups were compared by cognitive tests on attention, memory, executive function and fluid intelligence. Individuals with former amphetamine dependence performed significantly poorer than controls in memory domain. Follow-up analysis of variance showed minor deficits in tests of delayed verbal memory. The results remained essentially the same when participants with current DSM-IV axis I diagnosis were excluded from the analysis. It is concluded that individuals with former amphetamine dependence have normal cognitive function with the possible exception of verbal memory. Thus, if widespread cognitive deficits are found in individuals with former amphetamine dependence, etiologies other than amphetamine abuse as such should be carefully investigated.

Adult↗