Biomedical subjects

E Pekkonen

Publications and source records attributed to E Pekkonen.

At least 19 recordsLinked to original sources

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

Global field power of auditory N1 correlates with impaired verbal-memory performance in human alcoholics.

First weeks after alcohol withdrawal, associated with profound changes in neural transmission, constitute the critical period for relapse prevention and pharmacological intervention in alcoholism. Here, 20 male alcoholics with 1-6 weeks of abstinence and 20 age-matched healthy controls were studied using auditory event-related potentials (ERP), measured with a 32-channel electroencephalogram, and neuropsychological tests of auditory-verbal memory. Global field power maximum of ERP during 80-150 ms period after presentation of unattended tones (binaural 700 Hz pure tones, inter-stimulus interval 2.5 s) was significantly (P<0.01) larger in the alcoholics than controls. This effect, reflecting augmented N1 generation, significantly correlated (r=0.5) with impaired memory performance in the alcoholics. The profound change in pre-attentive auditory processing, predicting impaired memory performance, might reflect impaired cerebral inhibitory transmission in alcoholics.

Adult↗

PubMed2000

Dose-dependent suppression by ethanol of transient auditory 40-Hz response.

RATIONALE: Acute alcohol (ethanol) challenge is known to induce various cognitive disturbances, yet the neural basis of the effect is poorly known. The auditory transient evoked gamma-band (40-Hz) oscillatory responses have been suggested to be associated with various perceptual and cognitive functions in humans; however, alcohol effects on auditory 40-Hz responses have not been investigated to date. OBJECTIVES: The objective of the study was to test the dose-related impact of alcohol on auditory transient evoked 40-Hz responses during a selective-attention task. METHODS: Ten healthy social drinkers ingested, in four separate sessions, 0.00, 0. 25, 0.50, or 0.75 g/kg of 10% (v/v) alcohol solution. The order of the sessions was randomized and a double-blind procedure was employed. During a selective attention task, 300-Hz standard and 330-Hz deviant tones were presented to the left ear, and 1000-Hz standards and 1100-Hz deviants to the right ear of the subjects (P=0. 425 for each standard, P=0.075 for each deviant). The subjects attended to a designated ear, and were to detect the deviants therein while ignoring tones to the other ear. RESULTS: The auditory transient evoked 40-Hz responses elicited by both the attended and unattended standard tones were significantly suppressed by the 0.50 and 0.75 g/kg alcohol doses. CONCLUSIONS: Alcohol suppresses auditory transient evoked 40-Hz oscillations already with moderate blood alcohol concentrations. Given the putative role of gamma-band oscillations in cognition, this finding could be associated with certain alcohol-induced cognitive deficits.

Acoustic Stimulation↗

PubMed1999

Scopolamine augments transient auditory 40-hz magnetic response in humans.

The influence of neocortical muscarinic transmission on auditory-evoked 40-Hz magnetic response was studied in 13 healthy subjects in a double-blind randomized cross-over design. Either a centrally (scopolamine hydrobromide, 0.3 mg, i.v.) or a peripherally (glycopyrrolate, 0.2 mg, i.v.) acting antagonist of muscarinic transmission was administered during two sessions of magnetoencephalographic recording of 40-Hz response elicited by monaural tones. Scopolamine significantly (P < 0.01) augmented the 40-Hz magnetic response over the hemispheres ipsi- and contralateral to the ear stimulated. This finding suggests muscarinic modulation of the auditory evoked transient 40-Hz response.

Adult↗

PubMed1999

Post-withdrawal changes in middle-latency auditory evoked potentials in abstinent human alcoholics.

We investigated the effects of chronic alcoholism on middle-latency auditory evoked potentials (MAEP) in 14 male alcoholics with 1-6 weeks of abstinence (without other severe disorders) and 13 age-matched male social-drinker controls. The peak amplitude of a positive deflection (Pa) of the MAEP, peaking at about 30 ms post-stimulus, was significantly larger in the alcoholics than in the controls (P < 0.01), and notably, a significant negative correlation (r = -0.65) was observed between the Pa amplitude and duration of abstinence in the alcoholics. The present results suggest that the post-withdrawal brain hyperexcitability in the alcoholic brain, gradually recovering with abstinence, could be objectively and non-invasively studied with the MAEP.

Adult↗

PubMed1999

Benzodiazepine temazepam suppresses the transient auditory 40-Hz response amplitude in humans.

To discern the role of the GABA(A) receptors in the generation and attentive modulation of the transient auditory 40-Hz response, the effects of the benzodiazepine temazepam (10 mg) were studied in 10 healthy social drinkers, using a double-blind placebo-controlled design. Three hundred Hertz standard and 330 Hz rare deviant tones were presented to the left, and 1000 Hz standards and 1100 Hz deviants to the right ear of the subjects. Subjects attended to a designated ear and were to detect deviants therein while ignoring tones to the other. Temazepam significantly suppressed the amplitude of the 40-Hz response, the effect being equal for attended and non-attended tone responses. This suggests involvement of GABA(A) receptors in transient auditory 40-Hz response generation, however, not in the attentive modulation of the 40-Hz response.

Adult↗

PubMed1999

Decay of cortical pre-attentive sound discrimination in middle-age.

Ageing effects on pre-attentive cortical detection of sound change, as indexed by magnetic mismatch negativity (MMNm), were disclosed with whole-head magnetoencephalography (MEG). Seventy healthy subjects (aged 17-82 years) were presented with a sequence of homogeneous standard tones and occasional deviants of shorter duration. The MMNm elicited by the shorter tones was diminished in amplitude (r = -0.42, p < 0.001) and increased in latency in the hemisphere ipsilateral to the ear stimulated (r = 0.38, p < 0.01), these effects being significant even in middle-aged subjects. The results suggest that pre-attentive comparison of incoming stimuli to a short-lived sensory memory trace in the central auditory system is impaired, and delayed in the ipsilateral hemisphere, already by the middle-age.

Acoustic Stimulation↗

PubMed1999

Scopolamine enhances middle-latency auditory evoked magnetic fields.

To study the influence of central cholinergic muscarinic transmission on human cortical middle-latency auditory evoked magnetic fields (MAEF), centrally acting antagonist scopolamine hydrobromide (0.3 mg, i.v.), and peripheral muscarinic receptor antagonist glycopyrrolate (0.2 mg, i.v.), were administered to 13 healthy subjects in a double-blind randomized cross-over design. MAEF, measured with whole-head magnetoencephalography (MEG), were elicited with clicks applied at 10-Hz rate to the left ear. The amplitudes of N(b)m and P(a)m responses were augmented by scopolamine (P < 0.01 and P < 0.08). These effects were about equally strong for responses from ipsi- and contralateral auditory cortices. Thus, the present MEG findings revealed specific modulation of cortical generators of middle-latency auditory evoked responses by muscarinic transmission. These findings might be associated with auditory processing deficits observed in dementias with cholinergic disturbances.

Acetylcholine↗

PubMed1999

Impaired preconscious auditory processing and cognitive functions in Alzheimer's disease.

OBJECTIVE: To study whether preconscious auditory processing is deteriorated in patients with Alzheimer's disease (AD) having mild to moderate cognitive symptoms. To investigate whether auditory processing correlates with the impairment of the higher cortical functions. METHODS: P50m and N100m responses elicited by a sequence of repetitive tones were recorded with a whole-head magnetometer from 22 patients with probable AD and from 18 healthy age-matched controls. In addition, an extensive neuropsychological test battery assessing main cognitive domains was administered to all subjects. RESULTS: The patients with AD had significantly delayed N100m responses in the left hemisphere that correlated with the impairment of the language functions. CONCLUSIONS: N100m auditory responses measured with magnetoencephalography may be useful in evaluating the severity and progression of the cortical dysfunction in dementia.

Aged↗

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↗

PubMed1999

Suppression of mismatch negativity by backward masking predicts impaired working-memory performance in alcoholics.

BACKGROUND: Pronounced disruption of memory traces by subsequent distractors may result in impaired behavioral memory performance in alcoholics. METHODS: This hypothesis was investigated with an electrophysiological index of auditory sensory-memory traces, mismatch negativity, a preattentive event-related potential component elicited by a "deviant" tone within a train of "standard" tones. RESULTS: Inserting a masking stimulus after these tones abolished mismatch negativity in alcoholics (DSM-IV) but not in social-drinker controls. This effect predicted working-memory impairment in alcoholics, and correlated significantly with self-reported alcohol consumption of the subjects. Furthermore, the backward-masking mismatch negativity paradigm detected sensory-memory impairment in 9 of 20 alcoholics (sensitivity 45%), whereas all 20 social drinkers were unimpaired (specificity 100%). CONCLUSIONS: Vulnerability to memory trace disruption by shortly following sounds may be one of the factors contributing to behavioral memory dysfunction in alcoholics. The present result may provide an objective neurophysiological tool for investigation of alcohol-induced and other degenerative brain disorders.

Adult↗

PubMed1998

Parkinson's disease selectively impairs preattentive auditory processing: an MEG study.

Auditory stimuli elicit auditory evoked magnetic fields (AEFs) called P50m and N100m, which index preconscious auditory processing in human. We investigated with a whole-head magnetometer whether Parkinson's disease (PD) impairs parallel preattentive auditory processing between the hemispheres. Stimulus blocks consisting of standard (80%) and deviant (20%) tones were monaurally presented in a passive condition to 11 PD patients with unilateral motor symptoms and to 11 age-matched healthy controls. The constant interstimulus intervals (ISIs) were 0.5 s and 2.5 s in separate blocks. The interhemispheric latency differences of the P50m and N100m were significantly lengthened in PD patients in the left-ear condition. This might be caused by the basal ganglia dysfunction in PD together with the simultaneous age-related neural degeneration predominant in the left auditory cortex.

Acoustic Stimulation↗

PubMed1998

Reversal of cerebral asymmetry in schizophrenia measured with magnetoencephalography.

It has been suggested that schizophrenic patients fail to develop left-hemisphere dominance because of an early disturbance in neuronal development. This hypothesis has been supported by some post-mortem. CT and magnetic resonance imaging (MRI) studies, while other in-vivo studies have given contradicting results. We used 122-channel whole-head magnetoencephalography and MRI to locate the sources of auditory evoked responses in 19 schizophrenic patients and in 20 healthy controls. Auditory evoked responses were detected in all subjects. The left-right hemisphere asymmetry of cerebral sources for auditory evoked responses was markedly dispersed among patients when compared with controls. The source locations for left auditory cortex were clearly anterior with respect to the right hemisphere in 32% of the patients, while the corresponding prevalence of this abnormal asymmetry was 0% in controls (p = 0.008. Fisher's exact test). The reversed asymmetry appeared to be associated with a shorter anterior-posterior distance between the auditory cortex and the anterior tip of the temporal lobe in the left side when compared with the right side. The reversed asymmetry was associated with higher PANSS general psychopathological score, and especially with higher guilt feelings and motor retardation scores. The large 2.5-fold standard deviation in the inter-hemispheric anterior posterior difference in the location of the auditory cortex among patients (p 0.001 for the difference in the magnitude of variance between controls and patients) clearly reflects the dispersion of the left right asymmetry into both direction, and three of the patients with 'normal asymmetry' had a greater left-right asymmetry than any of the controls. Markedly greater reversal of hemispheric asymmetry among patients implies that regulation of the development of brain asymmetry is disturbed among schizophrenic patients. Abnormality in the cerebral asymmetry may be a crucial factor in the development of schizophrenic disorder in a substantial proportion of patients. The results suggest that the reversed asymmetry is associated with the higher severity of general psychopathological symptoms.

Adult↗

PubMed1998

Replicability of MEG and EEG measures of the auditory N1/N1m-response.

We investigated the replicability of the source location, amplitude and latency measures of the auditory evoked N1 (EEG) and N1m (MEG) responses. Each of the 5 subjects was measured 6 times in two recording sessions. Responses to monaural stimuli were recorded from 122 MEG and 64 EEG channels simultaneously. The EEG data were modeled with a symmetrically-located dipole pair. For the MEG data, one dipole in each hemisphere was located independently using a subset of channels. Standard deviation (SD) was used as a measure for replicability. The average SD of the x, y and z coordinates of the contralateral N1m dipole was about 2 mm, whereas the corresponding figures for the ipsilateral N1m and the contra- and ipsilateral N1 were about twice as large. The SDs of the dipole amplitudes and latencies were almost equal with MEG and EEG. The amplitude and latency measures of the MEG field gradient waveforms were almost as replicable as those of the dipole models. The results suggest that both MEG and EEG can be used for investigating the simultaneous activity of the left and right auditory cortices independently, MEG being superior in certain experimental setups.

Acoustic Stimulation↗

PubMed1998

Combined mapping of human auditory EEG and MEG responses.

Auditory electric and magnetic P50(m), N1(m) and MMN(m) responses to standard, deviant and novel sounds were studied by recording brain electrical activity with 25 EEG electrodes simultaneously with the corresponding magnetic signals measured with 122 MEG gradiometer coils. The sources of these responses were located on the basis of the MEG responses; all were found to be in the supratemporal plane. The goal of the present paper was to investigate to what degree the source locations and orientations determined from the magnetic data account for the measured EEG signals. It was found that the electric P50, N1 and MMN responses can to a considerable degree be explained by the sources of the corresponding magnetic responses. In addition, source-current components not detectable by MEG were shown to contribute to the measured EEG signals.

Acoustic Stimulation↗

PubMed1998

Effects of naltrexone and ethanol on auditory event-related brain potentials.

Acute effects of ethanol (0.55 g/kg) and the opioid antagonist naltrexone (50 mg) on auditory event-related brain potentials (ERP) (i.e., electrical brain activity time-locked to sensory stimuli) were investigated in 13 healthy social drinkers, using a double-blind, placebo-controlled, design. The subjects' task was to attend to tones presented to a designated ear while ignoring tones to the other, and to detect deviant tones among the attended tones. When administered alone, naltrexone significantly reduced the amplitude of the later part of negative difference (Nd[l]), suggesting impaired selective attention. However, this effect might have been caused by naltrexone-induced nausea. Ethanol, when ingested alone, attenuated the amplitude of the N1, and increased the peak latencies of the mismatch negativity (MMN) and N2b that have been suggested to reflect automatic change detection in audition and allocation of attentional resources to processing of stimulus deviance, respectively. In contrast, the P1 amplitude was augmented by alcohol, but only when the tones were attended. When ethanol and naltrexone were simultaneously ingested, however, the alcohol-induced P1 amplitude augmentation was canceled, thus tentatively suggesting opioidergic mediation of this alcohol effect. In contrast, the MMN peak latency was increased significantly more in the interaction condition than in the ethanol condition, thus suggesting that the detrimental effects of alcohol on involuntary attention switching were augmented by naltrexone. Furthermore, the N2b amplitude was significantly suppressed in the interaction condition, suggesting attentional impairment.

Adult↗

PubMed1998

Selective acceleration of auditory processing in chronic alcoholics during abstinence.

Simultaneous auditory processing between the hemispheres was studied with a whole-head magnetometer in 13 abstinent chronic alcoholics and 10 healthy control subjects. Auditory stimuli were presented monaurally with interstimulus intervals of 0.5 and 2.5 sec in different blocks. The N100m response, which contributes to stimulus detection, was significantly accelerated in the hemisphere ipsilateral to the ear stimulated in abstinent alcoholics. The MMNm response reflecting automatic stimulus-change detection peaked earlier in alcoholics, and the ipsilateral N100m latency correlated significantly with the abstinence duration. These results suggest that auditory processing is accelerated in the auditory cortex ipsilateral to the stimulated ear in chronic abstinent alcoholics and that the accelerated processing is at least partly reversible. This may be caused by the hyperexcitation in the brain related to the ethanol withdrawal.

Adult↗

PubMed1998

Processing of novel sounds and frequency changes in the human auditory cortex: magnetoencephalographic recordings.

Whole-head magnetoencephalographic (MEG) responses to repeating standard tones and to infrequent slightly higher deviant tones and complex novel sounds were recorded together with event-related brain potentials (ERPs). Deviant tones and novel sounds elicited the mismatch negativity (MMN) component of the ERP and its MEG counterpart (MMNm) both when the auditory stimuli were attended to and when they were ignored. MMNm generators were located bilateral to the superior planes of the temporal lobes where preattentive auditory discrimination appears to occur. A subsequent positive P3a component was elicited by deviant tones and with a larger amplitude by novel sounds even when the sounds were to be ignored. Source localization for the MEG counterpart of P3a (P3am) suggested that the auditory cortex in the superior temporal plane is involved in the neural network of involuntary attention switching to changes in the acoustic environment.

Acoustic Stimulation↗