Biomedical subjects

Carlo Miniussi

Publications and source records attributed to Carlo Miniussi.

17 recordsLinked to original sources

PubMed2006

Sources of cortical rhythms in adults during physiological aging: a multicentric EEG study.

This electroencephalographic (EEG) study tested whether cortical EEG rhythms (especially delta and alpha) show a progressive increasing or decreasing trend across physiological aging. To this aim, we analyzed the type of correlation (linear and nonlinear) between cortical EEG rhythms and age. Resting eyes-closed EEG data were recorded in 108 young (Nyoung; age range: 18-50 years, mean age 27.3+/-7.3 SD) and 107 elderly (Nold; age range: 51-85 years, mean age 67.3+/-9.2 SD) subjects. The EEG rhythms of interest were 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), and beta 2 (20-30 Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography (LORETA). Statistical results showed that delta sources in the occipital area had significantly less magnitude in Nold compared to Nyoung subjects. Similarly, alpha 1 and alpha 2 sources in the parietal, occipital, temporal, and limbic areas had significantly less magnitude in Nold compared to Nyoung subjects. These nine EEG sources were given as input for evaluating the type (linear, exponential, logarithmic, and power) of correlation with age. When subjects were considered as a single group there was a significant linear correlation of age with the magnitude of delta sources in the occipital area and of alpha 1 sources in occipital and limbic areas. The same was true for alpha 2 sources in the parietal, occipital, temporal, and limbic areas. In general, the EEG sources showing significant linear correlation with age also supported a nonlinear correlation with age. These results suggest that the occipital delta and posterior cortical alpha rhythms decrease in magnitude during physiological aging with both linear and nonlinear trends. In conclusion, this new methodological approach holds promise for the prediction of dementia in mild cognitive impairment by regional source rather than surface EEG data and by both linear and nonlinear predictors.

Adolescent↗

PubMed2004

The role of the right dorsolateral prefrontal cortex in visual change awareness.

Recently, the neural correlates of change detection vs change blindness have been investigated using fMRI. Results revealed that conscious perception of change is associated with enhanced activity in a neural network comprising the parietal (bilateral) and right dorsolateral prefrontal (DLPF) cortex. Here, by means of repetitive transcranial magnetic stimulation (rTMS), we unveil the causal role of the right DLPF cortex in perceiving changes. When rTMS was applied to this area, change perception was impaired as compared to left DLPF rTMS and sham stimulation. This result is important as it shows, for the first time, that conscious change perception is associated with normal activity in the right DLPF cortex. Our findings are in agreement with a recent view emphasizing the role of frontal areas, in addition to classical ventral and dorsal pathways, in visual awareness.

Adult↗

PubMed2004

Age-related functional changes of prefrontal cortex in long-term memory: a repetitive transcranial magnetic stimulation study.

Neuroimaging findings suggest that the lateralization of prefrontal cortex activation associated with episodic memory performance is reduced by aging. It is still a matter of debate whether this loss of asymmetry during encoding and retrieval reflects compensatory mechanisms or de-differentiation processes. We addressed this issue by the transient interference produced by repetitive transcranial magnetic stimulation (rTMS), which directly assesses causal relationships between performance and stimulated regions. We compared the effects of rTMS (a rapid-rate train occurring simultaneously to the presentation of memoranda) applied to the left or right dorsolateral prefrontal cortex (DLPFC) on visuospatial recognition memory in 66 healthy subjects divided in two classes of age (<45 and >50 years). In young subjects, rTMS of the right DLPFC interfered with retrieval more than left DLPFC stimulation. The asymmetry of the effect progressively vanished with aging, as indicated by bilateral interference effects on recognition performance. Conversely, the predominance of left DLPFC effect during encoding was not abolished in elders, thus probing its causal role for encoding along the life span. Findings confirm that the neural correlates of retrieval modify along aging, suggesting that the bilateral engagement of the DLPFC has a compensatory role on the elders' episodic memory performance.

Adult↗

PubMed2004

Human cortical rhythms during visual delayed choice reaction time tasks. A high-resolution EEG study on normal aging.

Neuroimaging cognitive study of aging requires simple tasks ensuring a high rate of correct performances even in stressful neurophysiological settings. Here two simple delayed choice reaction time tasks were used to unveil event-related desynchronization (ERD) of theta (4-6 Hz) and alpha (6-12 Hz) electroencephalographic rhythms across normal aging. In the first condition, a cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). The explicit demand was visuo-spatial, but the retention could be also based on phonological and somatomotor coding. In the second condition, the cue stimulus remained available along the delay period. Correct performances were higher than 95% in both groups and tasks, although they were significantly better in young than elderly subjects (P < 0.03). During the delay period, theta and alpha ERD accompanying correct responses were recognized in the two groups, the alpha ERD being stronger and prolonged during the memory than non-memory task. On the other hand, the fronto-parietal theta and parietal alpha ERD were stronger in young than elderly subjects during both tasks. Notably, the frontal alpha ERD was negligible in elderly subjects. In conclusion, the present simple tasks unveiled in elderly compared to young subjects (i) a weaker involvement of (para)hippocampal-cortical circuits as revealed by theta ERD and (ii) a weaker involvement of "executive" thalamo-cortical circuits as revealed by frontal alpha ERD. These effects might worsen behavioral performances to the simple cognitive tasks with age. The present protocol is promising for the neuroimaging study of pathological aging.

Adult↗

PubMed2004

Sub-second "temporal attention" modulates alpha rhythms. A high-resolution EEG study.

In the present high-resolution electroencephalographic (EEG) study, event-related desynchronization/synchronization (ERD/ERS) of alpha rhythms was computed during an S1-S2 paradigm, in which a visual cue (S1) predicted a SHORT (600 ms) or LONG (1400 ms) foreperiod, preceding a visual go stimulus (S2) triggering right or left finger movement. Could orienting attention to a selective point in time influence the alpha rhythms as a function of the SHORT vs. LONG foreperiod? Stronger selective attentional modulations were predicted for the SHORT than LONG condition. EEG data from 54 channels were "depurated" from phase-locked visual evoked potentials and spatially enhanced by surface Laplacian estimation (i.e., final data analysis was conducted on 16 subjects having a sufficient number of artifact-free EEG single trials). Low-band alpha rhythms (about 6-10 Hz) were supposed to be related to anticipatory attentional processes, whereas high-band alpha rhythms (10-12 Hz) would indicate task-specific visuo-motor processes. Compared to the LONG condition (foreperiod), the SHORT condition induced a quicker and stronger ERS at low-band alpha rhythm (about 6-8 Hz) over midline and bilateral prefrontal, sensorimotor, and posterior parietal areas. In contrast, the concomitant high-band alpha (about 10-12 Hz) ERD/ERS showed no significant difference between the two conditions. In conclusion, temporal attention for a sub-second delay (800 ms) did modulate low-band alpha rhythm over large regions of both cortical hemispheres.

Adolescent↗

PubMed2004

Mapping distributed sources of cortical rhythms in mild Alzheimer's disease. A multicentric EEG study.

The study aimed at mapping (i) the distributed electroencephalographic (EEG) sources specific for mild Alzheimer's disease (AD) compared to vascular dementia (VaD) or normal elderly people (Nold) and (ii) the distributed EEG sources sensitive to the mild AD at different stages of severity. Resting EEG (10-20 electrode montage) was recorded from 48 mild AD, 20 VaD, and 38 Nold subjects. Both AD and VaD patients had 24-17 of mini mental state examination (MMSE). EEG rhythms were 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), and beta 2 (20-30 Hz). Cortical EEG sources were modeled by low resolution brain electromagnetic tomography (LORETA). Regarding issue i, there was a decline of central, parietal, temporal, and limbic alpha 1 (low alpha) sources specific for mild AD group with respect to Nold and VaD groups. Furthermore, occipital alpha 1 sources showed a strong decline in mild AD compared to VaD group. Finally, distributed theta sources were largely abnormal in VaD but not in mild AD group. Regarding issue ii, there was a lower power of occipital alpha 1 sources in mild AD subgroup having more severe disease. Compared to previous field studies, this was the first investigation that illustrated the power spectrum profiles at the level of cortical (macroregions) EEG sources in mild AD patients having different severity of the disease with respect to VaD and normal subjects. Future studies should evaluate the clinical usefulness of this approach in early differential diagnosis, disease staging, and therapy monitoring.

Aged↗

PubMed2004

Human cortical EEG rhythms during long-term episodic memory task. A high-resolution EEG study of the HERA model.

Many recent neuroimaging studies of episodic memory have indicated an asymmetry in prefrontal involvement, with the left prefrontal cortex more involved than the right in encoding, the right more than the left in retrieval (hemispheric encoding and retrieval asymmetry, or HERA model). In this electroencephalographic (EEG) high-resolution study, we studied brain rhythmicity during a visual episodic memory (recognition) task. The theta (4-6 Hz), alpha (6-12 Hz) and gamma (28-48 Hz) oscillations were investigated during a visuospatial long-term episodic memory task including an encoding (ENC) and retrieval (RET) phases. During the ENC phase, 25 figures representing interiors of buildings ("indoor") were randomly intermingled with 25 figures representing landscapes ("landscapes"). Subject's response was given at left ("indoor") or right ("landscapes") mouse button. During the RET phase (1 h later), 25 figures representing previously presented "indoor" pictures ("tests") were randomly intermingled with 25 figures representing novel "indoor" ("distractors"). Again, a mouse response was required. Theta and alpha EEG results showed no change of frontal rhythmicity. In contrast, the HERA prediction of asymmetry was fitted only by EEG gamma responses, but only in the posterior parietal areas. The ENC phase was associated with gamma EEG oscillations over left parietal cortex. Afterward, the RET phase was associated with gamma EEG oscillations predominantly over right parietal cortex. The predicted HERA asymmetry was thus observed in an unexpected location. This discrepancy may be due to the differential sensitivity of neuroimaging methods to selected components of cognitive processing. The strict relation between gamma response and perception suggests that retrieval processes of long-term memory deeply impinged upon sensory representation of the stored material.

Adult↗

PubMed2004

The differential involvement of inferior parietal lobule in number comparison: a rTMS study.

Number processing is known to involve several sites within the posterior regions of parietal cortex. Here, we investigated whether neural activity in the inferior parietal lobule (IPL) is essential for number processing, by observing the effects of interfering with its activity during the execution of a standard number comparison task. Subjects performance on the task was significantly slowed down when we delivered trains of repetitive transcranial magnetic stimuli (rTMS) to the posterior parietal scalp site overlying the left IPL, while rTMS did not affect the number comparison task if delivered to homologous, contralateral (right) IPL. In conclusion, the present findings add support to a growing body of evidence from neuropsychology and neuroimaging studies that the left inferior parietal lobule is an important component of the networks subserving the representation of quantity.

Adult↗

PubMed2004

Human cortical responses during one-bit short-term memory. A high-resolution EEG study on delayed choice reaction time tasks.

OBJECTIVE: We investigated whether a very simple short-term memory (STM) demand induces a visible change of EEG rhythms over the two hemispheres. METHODS: High-resolution EEG was obtained in young adults during two delayed choice reaction time tasks. In the STM condition, a simple cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). The task was visuo-spatial in nature. RESULTS: In the control (NSTM) condition, the cue stimulus remained available along the delay period. Compared to the control condition, the theta power (4-6 Hz) decreased in left frontal and bilateral parietal areas (delay period). Furthermore, low alpha power (6-8 Hz) decreased in bilateral frontal and left parietal areas, while high alpha power (10-12 Hz) decreased in the left fronto-parietal areas. CONCLUSIONS: The decrease of the alpha power is as an expression of the efficient information transfer within thalamo-cortical pathways. The significance of the study stands in the fact that even a very simple STM task (only one bit to be memorized) revealed changes in fronto-parietal theta and alpha rhythms.

Adult↗

PubMed2004

Individual analysis of EEG frequency and band power in mild Alzheimer's disease.

OBJECTIVE: This EEG study investigates the role of the cholinergic system, cortico-cortical connections, and sub-cortical white matter on the relationship between individual EEG frequencies and their relative power bands. METHODS: EEGs were recorded at rest in 30 normal elderly subjects (Nold), 60 mild Alzheimer disease (AD) and 20 vascular dementia (VaD) patients, comparable for Mini Mental State Evaluation scores (MMSE 17-24). Individual EEG frequencies were indexed by the theta/alpha transition frequency (TF) and by the individual alpha frequency (IAF) with power peak in the extended alpha range (5-14 Hz). Relative power was separately computed for delta, theta, alpha1, alpha2, and alpha3 bands, on the basis of the TF and IAF. RESULTS: Using normal subjects as a reference, VaD patients showed 'slowing' of alpha frequency (TF-IAF) and lower alpha2 power; Mild AD patients showed lower alpha2 and alpha3 power; delta power was higher in both AD and VaD patients; Theta power was higher only in VaD patients. CONCLUSIONS: Individual analysis of the alpha frequency and power can discriminate mild AD from VaD and normal elderly subjects. SIGNIFICANCE: This analysis may probe pathophysiological mechanisms causing AD and VaD.

Aged↗

PubMed2004

Functional frontoparietal connectivity during short-term memory as revealed by high-resolution EEG coherence analysis.

In this electroencephalographic study, the authors modeled the functional connectivity between frontal and parietal areas during short-term memory (STM) processes by spectral coherence analysis and the directed transfer function, that is, for the estimation of coherence "direction." A no-STM task was used as a reference. STM was characterized by an increased frontoparietal electroencephalograph coherence at high frequencies (beta and gamma, 14-45 Hz). In the control task, parietal-to-frontal flow prevailed at those frequencies. However, the STM task showed a bidirectional frontoparietal flow at the gamma band. In conclusion, frontoparietal connectivity would optimize "representational" memory during STM. In this context, the frontal areas would increase their influence on parietal areas for memory retention.

Adult↗

PubMed2004

Cortical networks generating movement-related EEG rhythms in Alzheimer's disease: an EEG coherence study.

Patients with mild Alzheimer's disease (AD) present with abnormally strong values of frontal and ipsilateral central sensorimotor rhythms. The authors tested 2 working hypotheses of the related electroencephalographic (EEG) coherence: disconnection, defined as a sign of a reduced coordination within the frontoparietal and interhemispheric networks, and cooperation, defined as a reflection of the reorganization of the brain sensorimotor networks. Results showed that, compared with healthy controls, patients with mild AD had an unreactive and abnormally low interhemispheric EEG coherence and an unreactive and abnormally high frontoparietal EEG coherence. These findings support the hypothesis of an impaired mechanism of sensorimotor cortical coupling (disconnection) in mild AD.

Aged↗

PubMed2003

The role of prefrontal cortex in verbal episodic memory: rTMS evidence.

Long-term, episodic memory processing is supposed to involve the prefrontal cortex asymmetrically. Here we investigate the role of the dorsolateral prefrontal cortex (DLPFC) in encoding and retrieval of semantically related or unrelated word pairs. Subjects were required to perform a task consisting of two parts: a study phase (encoding), in which word pairs were presented, and a test phase (retrieval), during which stimuli previously presented had to be recognized among other stimuli. Consistently with our previous findings using pictures, repetitive transcranial magnetic stimulation (rTMS) had a significant impact on episodic memory. The performance was significantly disrupted when rTMS was applied to the left or right DLPFC during encoding, and to the right DLPFC in retrieval, but only for unrelated word pairs. These results indicate that the nature of the material to be remembered interacts with the encoding-retrieval DLPFC asymmetry; moreover, the crucial role of DLPFC is evident only for novel stimuli.

Adult↗

PubMed2003

Parietal lobe contribution to mental rotation demonstrated with rTMS.

A large number of imaging studies have identified a role for the posterior parietal lobe, in particular Brodmann's area 7 and the intraparietal sulcus (IPS), in mental rotation. Here we investigated whether neural activity in the posterior parietal lobe is essential for successful mental rotation performance by observing the effects of interrupting this activity during the execution of a mental rotation task. Repetitive transcranial magnetic stimulation (rTMS) was applied to posterior parietal locations estimated to overlie Brodmann's area 7 in the right and the left hemisphere, or to a posterior midline location (sham condition). In three separate experiments, rTMS (four pulses, 20 Hz) was delivered at these locations either 200-400, 400-600, or 600-800 msec after the onset of a mental rotation trial. Disrupting neural activity in the right parietal lobe interfered with task performance, but only when rTMS was delivered 400 to 600 msec after stimulus onset. Stimulation of the left parietal lobe did not reliably affect mental rotation performance at any of the time points investigated. The time-limited effect of rTMS was replicated in a fourth experiment that directly compared the effects of rTMS applied to the right parietal lobe either 200-400 or 400-600 msec into the mental rotation trial. The results indicate that the right superior posterior parietal lobe plays an essential role in mental rotation, consistent with its involvement in a variety of visuospatial and visuomotor transformations.

Adult↗

PubMed2002

Transient storage of a tactile memory trace in primary somatosensory cortex.

Working memory is known to involve prefrontal cortex and posterior regions of association cortex (e.g., the inferior temporal lobes). Here, we investigate the potential role of primary somatosensory cortex (SI) in a working memory task with tactile stimuli. Subjects were required to compare the frequencies of two vibrations separated by a retention interval of 1500 msec. Their performance was significantly disrupted when we delivered a pulse of transcranial magnetic stimulation (TMS) to the contralateral SI early (300 or 600 msec) in the retention interval. TMS did not affect tactile working memory if delivered to contralateral SI late in the retention interval (at 900 or 1200 msec), nor did TMS affect performance if delivered to the ipsilateral SI at any time point. Primary sensory cortex thus seems to act not only as a center for on-line sensory processing but also as a transient storage site for information that contributes to working memory.

Adult↗

PubMed2002

Watching where you look: modulation of visual processing of foveal stimuli by spatial attention.

Two experiments investigated the effect of sustained selective spatial attention upon the perceptual analysis of stimuli within the center of gaze. Spatial attention has typically been studied in relation to peripheral stimuli, and its relevance to the processing of central stimuli has remained relatively ignored. Here, behavioral measures in normal human volunteer participants showed that focused spatial attention can also influence responses to central stimuli, over and beyond the advantage conferred by their foveation. Event-related potentials (ERPs) showed that the action of attention upon foveal stimuli included the modulation of perceptual processing in extrastriate visual areas. Surprisingly, the visual modulation revealed an intriguing and consistent pattern of hemispheric asymmetry, in both experiments. These findings show that in addition to the established right hemisphere dominance of the brain areas that direct attention, the consequences of directed attention may also be asymmetrical.

Attention↗

PubMed2002

Multiple mechanisms of selective attention: differential modulation of stimulus processing by attention to space or time.

Two studies compared the modulatory effects of orienting attention to spatial locations versus temporal intervals using event-related potentials (ERPs). In both experiments subjects performed attentional orienting tasks, which used identical stimuli in both spatial and temporal orienting conditions. The first experiment (N=16) used bilateral peripheral targets (7.5 degrees eccentricity) at two different time intervals (600, 1200 ms after cue onset). During spatial orienting a symbolic central cue predicted (75% probability) the spatial location (left, right) of the relevant target. No information was given about the probable target interval (short, long). In temporal orienting the cue predicted the target interval but not its location. Valid cueing produced significantly shorter reaction times in both the spatial and temporal orienting conditions. ERPs to identical, non-target stimulus arrays were analysed, to isolate endogenous attentional mechanisms. Spatial and temporal attention had distinct modulatory effects upon stimulus processing. Focused spatial attention affected the amplitude of early visual components. Modulation by temporal attention started later, and mainly affected potentials linked to decisions and responses. The second experiment (N=12) used unilateral target stimuli, and equated the probability of stimulus occurrence at short and long time intervals and at left or right of fixation. The results confirmed the distinct pattern of modulation of stimulus processing by spatial and temporal orienting. The optimisation of behaviour by attention can thus be achieved as a consequence of distinct modulatory processes, illustrating the flexibility of attentional functions in the human brain.

Adult↗