Biomedical subjects

Vera Ferrari

Publications and source records attributed to Vera Ferrari.

6 recordsLinked to original sources

PubMed2006

The categorization of natural scenes: brain attention networks revealed by dense sensor ERPs.

The present study examined cortical indicators of selective attention underlying categorization based on target features in natural scenes. The primary focus was to determine the neural sources associated with the processing of target stimuli containing animals compared to non-target control stimuli. Neural source estimation techniques [current source density (CSD) and L2-minimum norm estimate (L2-MNE)] were used to determine the sources of the potential fields measured from 58 sensor sites. Assuring an excellent signal-to-noise ratio, the categorization task consisted of 2400 trials. Replicating previous findings, target and non-target ERP activity diverged sharply around 150 ms after stimulus onset and the early differential ERP activity appeared as positive deflection over fronto-central sensor sites and as negative deflection over temporo-occipital regions. Both source estimation techniques (CSD and L2-MNE) suggested primary sources of the early differential ERP activity in posterior, visual-associative brain regions and, although less pronounced, revealed the contribution of additional anterior sources. These findings suggest that selective attention to category-relevant features reflects the interactions between prefrontal and inferior temporal cortex during visual processing of natural scenes.

Adult↗

PubMed2006

Repetitive picture processing: autonomic and cortical correlates.

Emotionally arousing pictures elicit larger late positive potentials (LPPs) than neutral pictures during passive viewing. Moreover, these cortical responses do not rely on voluntary evaluation of the hedonic content and are relatively unaffected by task demands. In this study, we examined modulation of the late positive potential as it varies with stimulus repetition. Three pictures (pleasant, neutral, unpleasant) were presented up to 60 times each. Although the amplitude of the late positive potential during picture viewing declined with stimulus repetition, affective modulation remained intact. On the other hand, autonomic responses (skin conductance and heart rate change) habituated rapidly with stimulus repetition. These findings suggest that while stimulus detection and categorization, reflected in the LPP, is mandatory, autonomic modulation reflects initial orienting responses that habituate rapidly.

Adult↗

PubMed2006

Implicit and explicit categorization of natural scenes.

Event-related potential (ERP) studies have consistently found that emotionally arousing (pleasant and unpleasant) pictures elicit a larger late positive potential (LPP) than neutral pictures in a window from 400 to 800 ms after picture onset. In addition, an early ERP component has been reported to vary with emotional arousal in a window from about 150 to 300 ms with affective, compared to neutral stimuli, prompting significantly less positivity over occipito-temporal sites. Similar early and late ERP components have been found in explicit categorization tasks, suggesting that selective attention to target features results in similar cortical changes. Several studies have shown that the affective modulation of the LPP persisted even when the same pictures are repeated several times, when they are presented as distractors, or when participants are engaged in a competing task. These results indicate that categorization of affective stimuli is an obligatory process. On the other hand, perceptual factors (e.g., stimulus size) seem to affect the early ERP component but not the affective modulation of the LPP. Although early and late ERP components vary with stimulus relevance, given that they are differentially affected by stimulus and task manipulations, they appear to index different facets of picture processing.

Attention↗

PubMed2006

Sleep-dependent changes in cerebral oxygen consumption in newborn lambs.

During rapid-eye-movement (REM) sleep in adult subjects, the cerebral metabolic rate of oxygen consumption (CMRO(2)) is as high as that during wakefulness. We investigated whether CMRO(2) during active sleep is already at the waking level in newborn life, to support the role of active sleep as a state of endogenous brain activation during early postnatal development. Newborn lambs, 2-5 days old (n = 6), were instrumented with electrodes for sleep-state scoring, catheters for blood sample withdrawal and pressure monitoring, and a transit-time ultrasonic blood-flow probe around the superior sagittal sinus. At the age of 19 +/- 3 days, blood samples were obtained simultaneously from the carotid artery and the superior sagittal sinus during uninterrupted epochs of wakefulness, quiet sleep, and active sleep. The arteriovenous difference in blood oxygen concentration was multiplied by cerebral blood flow to determine CMRO(2). CMRO(2) during active sleep (47 +/- 5 micromol min(-1)) was similar to the value in wakefulness (44 +/- 6 micromol min(-1)) and significantly higher than in quiet sleep (39 +/- 5 micromol min(-1), P < 0.05). These data show that active sleep provides newborn lambs with brain activity at a level similar to that in wakefulness in terms of cerebral oxygen metabolism. The high CMRO(2) during active sleep supports its functional role during early postnatal development, when time spent in active sleep is at a lifetime maximum, albeit constituting a metabolic challenge for newborns, because of the impairment of systemic and cerebral vascular regulation in this sleep state.

Animals↗

PubMed2005

Sleep-related brain activation does not increase the permeability of the blood-brain barrier to glucose.

We compared blood-brain barrier (BBB) permeability to glucose between quiet wakefulness and rapid-eye-movement (REM) sleep to assess whether changes in BBB permeability play a role in coupling glucose supply to the physiologic metabolic needs of the brain. Male Sprague-Dawley rats were prepared with electrodes for wake-sleep state scoring and with arterial and venous catheters. Using the single-pass, dual-label indicator method, unidirectional glucose extraction by the brain and cerebral blood flow (CBF) were simultaneously measured during states of quiet wakefulness (n=12) or REM sleep (n=7). The product of BBB surface area and permeability to glucose (PS product) was computed in each state. During REM sleep, CBF significantly exceeded that during quiet wakefulness in all regions but the cerebellum, whereas the difference in the PS product between quiet wakefulness and REM sleep was not statistically significant in any brain region. In the brain as a whole, CBF significantly increased 29% from quiet wakefulness to REM sleep, while a nonsignificant 0.8% increase occurred in the PS product. During REM sleep, the increase in CBF indicates a higher rate of brain glucose consumption than in quiet wakefulness, given the tight flow-metabolism coupling in the brain. Therefore, these data show that modulation of BBB permeability to glucose is not a mechanism that provides 'energy on demand' during the physiologic brain activation characterising REM sleep.

Algorithms↗

PubMed2004

Sleep-dependent changes in the coupling between heart period and arterial pressure in newborn lambs.

This study assessed whether sleep-dependent changes in the relationship between heart period (HP) and mean arterial pressure (MAP) occur in newborn life. Electrodes for electrocorticographic, electromyographic, and electrooculographic monitoring and an arterial catheter for blood pressure recordings were implanted in 11 newborn lambs. HP and MAP beat-to-beat values were computed from 120-s blood pressure recordings during quiet wakefulness, active sleep, and quiet sleep. For each recording, the time shift at which the maximum of the HP versus MAP cross-correlation function was attained was identified. For each lamb and wake-sleep state, an average correlation coefficient was then computed corresponding to the median value of such time shifts. The maximum of the cross-correlation function was attained with HP lagging behind MAP. The corresponding mean correlation coefficient was significantly higher in quiet sleep (0.51 +/- 0.05) than either in quiet wakefulness (0.31 +/- 0.05) or in active sleep (0.29 +/- 0.03). Sleep-related differences in the correlation between HP and MAP were maintained after HP and MAP data were low-pass filtered at 0.3 Hz to remove their fast ventilatory oscillations. In conclusion, data indicate that the relationship between spontaneous fluctuations in HP and those in MAP is sleep-state dependent in newborn lambs. A positive HP versus MAP correlation with HP lagging behind MAP is consistent with baroreflex control of HP. Heart rhythm thus may be more tightly controlled by the baroreceptor reflex and less dependent on central autonomic commands in quiet sleep than either in quiet wakefulness or in active sleep.

Animals↗