Biomedical subjects

Carlo Miniussi

Publications and source records attributed to Carlo Miniussi.

28 records · Page 2Linked to original sources

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↗

PubMed2002

Interhemispheric transfer and laterality effects in simple visual reaction time in schizophrenics.

INTRODUCTION: There is evidence that schizophrenics have an abnormal corpus callosum and an abnormal pattern of cerebral asymmetries. We investigated whether there are corresponding functional abnormalities in interhemispheric transfer (IT) and laterality effects. METHODS: Medicated schizophrenic patients and matched controls were tested in the Poffenberger paradigm, that is, a simple manual reaction time (RT) paradigm with laterally presented visual stimuli designed to provide a behavioural estimate of IT. By subtracting RT averaged across the uncrossed hand-hemifield conditions, from RT averaged across the crossed hand-hemifield conditions, one can obtain an estimate of IT time. RESULTS: In schizophrenic patients the difference between crossed and uncrossed conditions was 0 because of an unusually prolonged RT in the uncrossed condition right hand/ right field. A broadly similar result has been obtained previously in the tactile modality (Ditchfield & Hemsley, 1990) and is consistent with a left hemisphere impairment. This effect was still present when the patients were retested about 2 years later. CONCLUSIONS: These results demonstrate the existence in schizophrenic patients of a consistent slowing down of simple visuomotor responses subserved by the left hemisphere.

Journal Article↗