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Biomedical subjects

C Miniussi

Publications and source records attributed to C Miniussi.

At least 19 recordsLinked to original sources
PubMed2006

Conversion from mild cognitive impairment to Alzheimer's disease is predicted by sources and coherence of brain electroencephalography rhythms.

Objective. Can quantitative electroencephalography (EEG) predict the conversion from mild cognitive impairment (MCI) to Alzheimer's disease (AD)? Methods. Sixty-nine subjects fulfilling criteria for MCI were enrolled; cortical connectivity (spectral coherence) and (low resolution brain electromagnetic tomography) sources of EEG rhythms (delta=2-4 Hz; theta=4-8 Hz; alpha 1=8-10.5 Hz; alpha 2=10.5-13 Hz: beta 1=13-20 Hz; beta 2=20-30 Hz; and gamma=30-40) were evaluated at baseline (time of MCI diagnosis) and follow up (about 14 months later). At follow-up, 45 subjects were still MCI (MCI Stable) and 24 subjects were converted to AD (MCI Converted). Results. At baseline, fronto-parietal midline coherence as well as delta (temporal), theta (parietal, occipital and temporal), and alpha 1 (central, parietal, occipital, temporal, limbic) sources were stronger in MCI Converted than stable subjects (P<0.05). Cox regression modeling showed low midline coherence and weak temporal source associated with 10% annual rate AD conversion, while this rate increased up to 40% and 60% when strong temporal delta source and high midline gamma coherence were observed respectively. Interpretation. Low-cost and diffuse computerized EEG techniques are able to statistically predict MCI to AD conversion.

Aged↗
PubMed2006

Transcranial magnetic stimulation and cortical evoked potentials: a TMS/EEG co-registration study.

OBJECTIVE: In recent years, a promising tool has been introduced which allows the co-registration of electroencephalographic (EEG) activity during brain transcranial magnetic stimulation (TMS). The aims of the present study are to identify eventual stimulus-related artefacts, and to confirm and extend previous EEG/TMS findings about the possible networks generating EEG responses evoked by TMS. METHODS: Focal TMS was delivered to the left primary motor cortex (MI), with different coils (real and sham) and orientations (45 and 135 degrees in respect to the sagittal plane), in six healthy subjects. EEG and motor evoked potentials (MEPs) were simultaneously recorded from 19 scalp electrodes. RESULTS: TMS, with coil oriented at 45 degrees , induced EEG responses characterized by a sequence of positive deflections peaking at approximately 14, 30, 60 and 190 ms and negative deflections peaking at approximately 10, 18, 40 and 100 ms post-TMS. The negative components were recorded at the recording electrode corresponding with the stimulation site (N10, N18), as well as at recording electrodes over the frontal region of the contralateral, unstimulated, hemisphere (N40) and bilaterally over the central hemispheres with its maximal representation at the stimulation site (N100). The positive components were instead detected at the frontal region of the right, unstimulated, hemisphere (P14), over the central electrodes Cz, Fz and the frontal region of the right hemisphere (P30), at the stimulation site (P60), and over the frontal regions of both hemispheres. When TMS was delivered with the coil oriented at 135 degrees , no MEPs were recorded from the right target muscle. Nonetheless, all the TMS-induced EEG components were still evoked apart from the N20-P30. Finally, TMS with the sham coil over left MI did not induce either significant EEG responses or MEPs. CONCLUSIONS: In conclusion, the TMS evoked components we have obtained by recording in continuous mode strikingly fit with those already described by other authors for both their latencies and the spatio-temporal pattern of scalp distribution. SIGNIFICANCE: This experiment is a farther validation of the combined EEG/TMS recording technique as a promising tool for experimental and clinical purposes.

Adult↗
PubMed2005

Modulation of brain activity by selective task sets observed using event-related potentials.

We investigated the ability of subjects to shift dynamically between selective task sets, using informative trial-by-trial cues. Two tasks were used which involved non-overlapping neural systems and different hemispheric specialization. In a verbal task, subjects decided whether a letter string was a real word or a non-word. In a spatial task, subjects decided whether an angle was acute or obtuse. A behavioural experiment showed that performance improved when cues predicted the upcoming task (80% validity), compared to when neutral cues did not afford selective task sets. Event-related potentials (ERPs) revealed brain activity related to forming selective task expectations, to switching tasks, and to the modulation of target processing as a function of such expectations and switches. Activity predicting the probable task started over parietal electrodes 160 ms after cue presentation, while activity related to task switching started at frontal electrodes around 280 ms. Both types of activities developed before target onset. Target processing was significantly influenced by the validity of the cue prediction, including strong modulation of language-related potentials. These results show that it is possible to switch dynamically between task sets involving distinct neural systems, even before the appearance of an imperative target stimulus, and that the nature of the task sets can influence neural activity related to task-set reconfiguration. Selective task sets can in turn modulate the processing of target stimuli. The effects also apply to the case of foveally presented words, whose processing has often been hypothesized to be automatic and outside the influence of selective attention.

Adult↗
PubMed2005

Repetitive transcranial magnetic stimulation (rTMS) at high and low frequency: an efficacious therapy for major drug-resistant depression?

OBJECTIVE: Repetitive transcranial magnetic stimulation (rTMS) is proposed for the treatment of drug-resistant depression. Studies performed in accordance with evidence-based medicine (EBM) are scarce, particularly in seeking optimal treatment and evaluation parameters. We aimed to test various types of rTMS in a large sample of depressed patients following EBM rules and to investigate treatment-related changes in plasma levels of neurotransmitters involved in depression. METHODS: Seventy-one drug-resistant depressed patients were randomly assigned to low (1 Hz) or high (17 Hz) rate TMS, applied for 5 days over the left dorsolateral prefrontal cortex (L-DLPFC). Patients were separated into two study designs. One group (20 patients) received only active treatment, while the other entered a double-blind, placebo-controlled, crossover design. Pre- and post-treatment blood samples were taken for evaluation of plasma levels of dopamine and serotonin. RESULTS: After a week of treatment patients had a measurable benefit. However, overall the placebo stimulation did not differ significantly from real stimulation, nor were differences observed between the two rates of rTMS. The only difference emerged when the real stimulation was applied at 17 Hz following placebo treatment. Plasma levels of neurotransmitters between active and placebo rTMS were similar. CONCLUSIONS: Using the treatment schedule of 1 week, although a clinical improvement after active treatment was indeed observed, this was both clinically and biochemically indistinguishable from that seen in the placebo arm. SIGNIFICANCE: This suggests that most of the previous emphasis, for short period of treatment, should be tempered down and that further work is required in order to verify whether optimal stimulation and evaluation parameters for TMS-treatment of depression beyond the placebo effect may be found following EBM rules.

Adult↗
PubMed2004

EEG deblurring techniques in a clinical context.

OBJECTIVES: EEG scalp potential distributions recorded in humans are affected by low spatial resolution and by the dependence on the electrical reference used. High resolution EEG technologies are available to drastically increase the spatial resolution of the raw EEG. Such technologies include the computation of surface Laplacian (SL) of the recorded potentials, as well as the use of realistic head models to estimate the cortical sources via linear inverse procedure (low resolution brain electromagnetic tomography, LORETA). However, these deblurring procedures are generally used in conjunction with EEG recordings with 64-128 scalp electrodes and with realistic head models obtained via sequential magnetic resonance images (MRIs) of the subjects. Such recording setup it is not often available in the clinical context, due to both the unavailability of these technologies and the scarce compliance of the patients with them. In this study we addressed the use of SL and LORETA deblurring techniques to analyze data from a standard 10-20 system (19 electrodes) in a group of Alzheimer disease (AD) patients. METHODS: EEG data related to unilateral finger movements were gathered from 10 patients affected by AD. SL and LORETA techniques were applied for source estimation of EEG data. The use of MRIs for the construction of head models was avoided by using the quasi-realistic head model of the Brain Imaging Neurology Institute of Montreal. RESULTS: A similar cortical activity estimated by the SL and LORETA techniques was observed during an identical time period of the acquired EEG data in the examined population. CONCLUSIONS: The results of the present study suggest that both SL and LORETA approaches can be usefully applied in the clinical context, by using quasi-realistic head modeling and a standard 10-20 system as electrode montage (19 electrodes). These results represent a reciprocal cross-validation of the two mathematically independent techniques in a clinical environment.

Aged↗
PubMed2002

The role of the left frontal lobe in action naming: rTMS evidence.

BACKGROUND: Neuropsychological and neuroimaging studies suggest that whereas the left temporal neocortex plays a crucial role in all tasks involving lexical-semantic processing, some regions of the left prefrontal convexity are selectively recruited during verb processing. OBJECTIVE: To determine if there are different neural correlates for noun and verb processing in the human brain. METHODS: Repetitive transcranial magnetic stimulation (rTMS), 20 Hz at 90% of the motor threshold, was applied to left or right prefrontal brain during object- and action-naming tasks in nine healthy subjects. RESULTS: A shortening of naming latency for actions was observed only after stimulation of left prefrontal cortex. CONCLUSION: The involvement of the left dorsolateral frontal cortex in action naming was demonstrated using rTMS.

Adult↗
PubMed2001

Orienting attention in time.

Temporal information is essential for effective perception and action in the dynamic environment in which we exist. However, our ability to use information about time intervals flexibly to direct attention to an expected point in time has until recently been unexplored. Here we report a series of behavioural, neuroimaging and electrophysiological experiments that investigate and define the ability to orient attention in the temporal domain. These studies reveal that we are able to orient attention selectively to different time intervals, enhancing behavioural performance. These effects are mediated by a left-hemisphere dominant frontal-parietal system, which partially overlaps with the networks involved in spatial orienting. The optimisation of behaviour by temporal orienting appears to be achieved via motor-related mechanisms, in contrast to the typical perceptual enhancements produced by spatial attention. From a more general perspective, these findings illustrate the flexibility of attentional functions in the human brain.

Adaptation, Psychological↗
PubMed2001

What exactly is extinguished in unilateral visual extinction? Neurophysiological evidence.

We propose a model of unilateral visual extinction following right hemisphere lesions based on competition between contralesional and ipsilesional input to access a decision centre located in the left hemisphere. During bilateral presentations, the contralesional signal is on average less likely to activate the decision centre than the ipsilesional signal. This is because an intra-hemispheric lack of top-down attentional influences and an inter-hemispheric impairment of callosal transmission delay and/or weaken the contralesional input. Here we provide behavioural as well as event-related potential evidence for both these impairments. Finally, we argue that an essential prerequisite for contralesional extinction is the presence of a restricted general attentional capacity which often follows large right hemisphere damage.

Adolescent↗
PubMed2001

Prefrontal [correction of Prefontal] cortex in long-term memory: an "interference" approach using magnetic stimulation.

Neuroimaging has consistently shown engagement of the prefrontal cortex during episodic memory tasks, but the functional relevance of this metabolic/hemodynamic activation in memory processing is still to be determined. We used repetitive transcranial magnetic stimulation (rTMS) to transiently interfere with either left or right prefrontal brain activity during the encoding or retrieval of pictures showing complex scenes. We found that the right dorsolateral prefrontal cortex (DLPFC) was crucial for the retrieval of the encoded pictorial information, whereas the left DLPFC was involved in encoding operations. This 'interference' approach allowed us to establish whether a cortical area activated by a memory task actually contributes to behavioral performance.

Adult↗
PubMed2000

The dynamics of shifting visuospatial attention revealed by event-related potentials.

We developed a behavioral task for spatial orienting of attention in which the same physical stimulus cued covert peripheral shifts of attention to either the left or the right visual fields in different conditions. The design enabled us to record the brain activity engaged during spatial shifts of covert attention that was independent from the physical characteristics of the cueing stimulus using event-related potentials (ERPs). ERPs elicited by foveal cues differed according to the predicted target location starting ca. 160 ms, and differences persisted until the occurrence of the target stimuli. Multiple processes were linked to shifting spatial attention during the cue-target interval. The earliest effects consisted of enhanced negative potentials over the posterior scalp contralateral to the cued location. Later effects were concentrated over the right anterior scalp sites, where activity associated with shifts to the right visual field elicited larger positive potentials. The results extend our understanding of the neural system that orients spatial attention by providing valuable information about the temporal dynamics and hemispheric asymmetries of activity within its posterior and anterior regions.

Adult↗
PubMed2000

Electrophysiological correlates of conscious vision: evidence from unilateral extinction.

To study the electrophysiological correlates of conscious vision, we recorded event-related potentials (ERPs) in a patient with partial unilateral visual extinction as a result of right-hemisphere damage. When, following bilateral presentations, contralesional stimuli were not perceived, there was an absence of the early attention-sensitive P1 (80-120 msec) and N1 (140-180 msec) components of the ERP response. In contrast, following unilateral presentations, or in those bilateral presentations in which contralesional stimuli were perceived (about 60%), these ERP components were present. These results provide novel evidence that extinction involves the stage of early focusing of attention and that the P1 and N1 components of visual ERPs are reliable physiological correlates of conscious vision.

Attention↗
PubMed1999

Pathways of interhemispheric transfer in normals and in a split-brain subject. A positron emission tomography study.

We studied with PET the intra- and interhemispheric pathways subserving a simple, speeded-up visuomotor task. Six normal subjects and one patient with a complete section of the corpus callosum (M.E.) underwent regional cerebral blood flow (rCBF) measurements under conditions of lateralized tachistoscopic visual presentations in a simple manual reaction time paradigm. Confirming previous behavioural findings, we found that on average crossed hand and/or hemifield conditions, i.e. those requiring an interhemispheric transfer of information, yielded a longer RT than uncrossed conditions. This difference (0.7 ms) was dramatically larger (45.6 ms) in the callosum-sectioned patient M.E. In normal subjects the cortical areas selectively activated in uncrossed and crossed conditions were different. In the former condition, most activation foci were anterior to the ventral anterior commissure (VAC) plane, whereas in the latter there was a prevalent parietal and occipital activation. This shows that a simple model in which the cortical visuo-motor pathways are similar in the intra- and the interhemispheric condition, with an extra callosal route for the latter, is too simplistic. Furthermore, these results suggest that the bulk of visuomotor interhemispheric transfer takes place through the widespread callosal fibres interconnecting the parietal cortices of the two hemispheres. The pattern of activation in the two crossing conditions was markedly different in M.E., in whom interhemispheric transfer might take place via his intact anterior commissure or subcortical commissures.

Adult↗
PubMed1999

Orienting attention in time. Modulation of brain potentials.

With the aim of casting light on the neural mechanisms that support our ability to modulate visual attention over time, we recorded event-related potentials (ERPs) while normal human subjects performed a target detection task with temporal contingencies between cue and target stimuli. The task used two central cues, which predicted (80% validity) when a subsequent target would occur (either 600 or 1400 ms after cue onset). Unlike previous tasks of attentional orienting, there was no spatial information provided and all stimuli were presented foveally. Reaction times and ERPs linked to targets presented at the shorter interval showed significant effects linked to attentional orienting. Reaction times were faster when the cues correctly predicted the cue-target interval, suggesting the ability of the brain to use information about time to deploy attentional resources. ERPs differed according to the predicted time interval. In particular, the P300 amplitude and latency were enhanced when the cue predicted the cue-target interval accurately. The ERPs elicited by the cues also differed according to the time interval that they predicted. Differences were observed in potentials linked to motor preparation and expectancies. The results reveal dynamic neural activity involved in orienting attention to time intervals, as well as the consequent modulation of target-related neural activity resulting from differing temporal expectations.

Adult↗
PubMed1998

Transcranial magnetic stimulation selectively impairs interhemispheric transfer of visuo-motor information in humans.

We investigated the cerebral cortical route by which visual information reaches motor cortex when visual signals are used for manual responses. Subjects responded unimanually to photic stimuli delivered to the hemifield ipsilateral or contralateral to the moving hand. On some trials, trans-cranial magnetic stimulation (TMS) was applied unilaterally over the occiput, with the aim of stimulating extrastriate visual areas and thereby modifying transmission of visual input. In association with the side of a visual stimulus and a motor response, TMS could change inter- or intra-hemispheric transmission needed to convey visual information to motor areas. Reaction time differences following TMS suggested that TMS exerted an inhibitory effect only when visuo-motor information had to be transferred interhemispherically. This result reinforces evidence for an extrastriate pathway of interhemispheric transfer of visuomotor information.

Acoustic Stimulation↗
PubMed1998

Scalp topography and source analysis of interictal spontaneous spikes and evoked spikes by digital stimulation in benign rolandic epilepsy.

OBJECTIVES: We report the analysis of scalp topography and dipole modeling of the rolandic spikes in 6 patients suffering of benign rolandic epilepsy of childhood with extremely high amplitude SEP by tapping stimulation of the finger of the hand. METHODS: EEG and BESA analysis were performed for both rolandic spontaneous interictal spikes and high amplitude scalp activity evoked by tapping and electrical stimulation of the first finger of the right hand. RESULTS: The evoked responses showed a morphology characterized by a rapid phase (spike) followed by a slow phase (slow wave). The spike presented an early small positive component followed by a main negative component. Similar morphology, dipole configuration and source localization were observed for both rolandic spikes and evoked high amplitude scalp responses. Dipole localization showed an overlap of spatial coordinates between rolandic and evoked spikes. CONCLUSIONS: These findings suggest that the extremely high amplitude SEPs could be evoked spikes which probably had the same cortical generators of the spontaneous rolandic spikes.

Brain Mapping↗
PubMed1998

Spike topography and functional magnetic resonance imaging (fMRI) in benign rolandic epilepsy with spikes evoked by tapping stimulation.

We performed a spike topography study and a functional magnetic resonance imaging (fMRI) in a female patient with benign rolandic epilepsy presenting single high-amplitude evoked spikes in response to somatosensory peripheral stimulation. The stimulus was delivered to the first finger of the right hand using a tendon hammer, which evoked a single spike followed by a slow wave, showing the maximal amplitude over the left central regions. fMRI showed that the contralateral sensory cortices (S1 and S2) and the motor cortex (M I) were activated during tapping stimulation. In 3 normal subjects, tapping stimulation produced no fMRI activation. This fMRI study documents a highly focal activation of sensorimotor areas related to subclinical evoked spikes in benign rolandic epilepsy.

Acoustic Stimulation↗
PubMed1998

Influence of somatosensory input on paroxysmal activity in benign rolandic epilepsy with 'extreme somatosensory evoked potentials'.

We studied six patients suffering from benign rolandic epilepsy of childhood with central temporal spikes who presented so-called 'extreme somatosensory evoked potentials (SEPs)' following peripheral somatosensory stimulation. Stimuli were delivered to the fingers of one hand using both a triggered tendon hammer and low-intensity electrical stimulation. The electrical stimulation was delivered in sequences in different conditions (i.e. random order, 1, 3 and 10 Hz). Both tapping and electrical stimulation produced scalp evoked potentials in all subjects, characterized by a spike followed by a slow wave, similar in morphology and scalp distribution to the spontaneously occurring spikes. This paroxysmal activity was sensitive to stimulus rate; the number of evoked spikes was inversely related to the frequency of stimulation, being maximal at 1 Hz and disappearing at high frequencies (10 Hz). Spontaneous spikes disappeared during high-frequency stimulation but were present during low-frequency stimulation. Averaged SEPs at 3-Hz stimulation showed a late high-amplitude component, identical in morphology and distribution to the single evoked spike. We therefore conclude that, in these subjects, the so-called 'extreme SEPs' are evoked spikes and that evoked and spontaneous spikes share common cortical sensorimotor generators. The evidence that these generators can be influenced by afferent input provides important information regarding the functional mechanisms involved in modulating cortical excitability in benign rolandic epilepsy. Moreover, we suggest that peripheral electrical stimulation can be used as an additional activation test in this kind of epilepsy.

Age of Onset↗