Biomedical subjects

Ivo Vanzetta

Publications and source records attributed to Ivo Vanzetta.

5 recordsLinked to original sources

PubMed2006

Behavioral receptive field for ocular following in humans: dynamics of spatial summation and center-surround interactions.

Visual neurons integrate information over a finite part of the visual field with high selectivity. This classical receptive field is modulated by peripheral inputs that play a role in both neuronal response normalization and contextual modulations. However, the consequences of these properties for visuomotor transformations are yet incompletely understood. To explore those, we recorded short-latency ocular following responses in humans to large center-only and center-surround stimuli. We found that eye movements are triggered by a mechanism that integrates motion over a restricted portion of the visual field, the size of which depends on stimulus contrast and increases as a function of time after response onset. We also found evidence for a strong nonisodirectional center-surround organization, responsible for normalizing the central, driving input so that motor responses are set to their most linear contrast dynamics. Such response normalization is delayed about 20 ms relative to tracking onset, gradually builds up over time, and is partly tuned for surround orientation/direction. These results outline the spatiotemporal organization of a behavioral receptive field, which might reflect a linear integration among subpopulations of cortical visual motion detectors.

Adult↗

PubMed2005

Compartment-resolved imaging of activity-dependent dynamics of cortical blood volume and oximetry.

Optical imaging, positron emission tomography, and functional magnetic resonance imaging (fMRI) all rely on vascular responses to image neuronal activity. Although these imaging techniques are used successfully for functional brain mapping, the detailed spatiotemporal dynamics of hemodynamic events in the various microvascular compartments have remained unknown. Here we used high-resolution optical imaging in area 18 of anesthetized cats to selectively explore sensory-evoked cerebral blood-volume (CBV) changes in the various cortical microvascular compartments. To avoid the confounding effects of hematocrit and oximetry changes, we developed and used a new fluorescent blood plasma tracer and combined these measurements with optical imaging of intrinsic signals at a near-isosbestic wavelength for hemoglobin (565 nm). The vascular response began at the arteriolar level, rapidly spreading toward capillaries and venules. Larger veins lagged behind. Capillaries exhibited clear blood-volume changes. Arterioles and arteries had the largest response, whereas the venous response was smallest. Information about compartment-specific oxygen tension dynamics was obtained in imaging sessions using 605 nm illumination, a wavelength known to reflect primarily oximetric changes, thus being more directly related to electrical activity than CBV changes. Those images were radically different: the response began at the parenchyma level, followed only later by the other microvascular compartments. These results have implications for the modeling of fMRI responses (e.g., the balloon model). Furthermore, functional maps obtained by imaging the capillary CBV response were similar but not identical to those obtained using the early oximetric signal, suggesting the presence of different regulatory mechanisms underlying these two hemodynamic processes.

Animals↗

PubMed2004

Columnar resolution of blood volume and oximetry functional maps in the behaving monkey; implications for FMRI.

The ultimate goal of high-resolution functional brain mapping is single-condition (stimulus versus no-stimulus maps) rather than differential imaging (comparing two "stimulus maps"), because the appropriate ("orthogonal") stimuli are rarely available. This requires some component(s) of activity-dependent hemodynamic signals to closely colocalize with electrical activity, like the early increase in deoxyhemoglobin, shown previously to yield high-quality functional single-condition maps. Conversely, nonlocal vascular responses dominate in cerebral blood volume (CBV)-based single-condition maps. Differential CBV maps are largely restricted to the parenchyma, implying that part of the CBV response does colocalize with electrical activity at fine spatial scale. By removing surface vascular activation from optical imaging data, we document the existence of a capillary CBV response component, regulated at fine spatial scale and yielding single-condition maps exhibiting approximately 100 microm resolution. Blood volume and -flow based single-condition functional mapping at columnar level should thus be feasible, provided that the capillary response component is selectively imaged.

Animals↗

PubMed2004

High-resolution functional optical imaging: from the neocortex to the eye.

Much work remains to be done to establish the clinical usefulness of the RFI for early diagnosis and treatment guidance. The discoveries obtained by functional optical imaging of the neocortex in the last 15 years and the recent RFI studies of the eyes of normal subjects and patients with diabetic retinopathy, glaucoma, and age-related macular degeneration suggest that functional optical imaging of the retina is likely to become a multi-modality powerful clinical tool.

Animals↗

PubMedDate not supplied

Special report: Noninvasive multi-parameter functional optical imaging of the eye.

Advancement in the treatment of blindness depends on the development of new technologies that enable early detection, follow-up, and treatment of disease. The authors describe direct, noninvasive imaging of four parameters: blood flow, blood oximetry, metabolic state, and hidden vasculature, particularly capillaries. These are functional parameters of the retina known to be degraded by retinal disease. The new Retinal Function Imager (Optical Imaging, Ltd., Rehovot, Israel) can image all four parameters as intrinsic reflectance intensity differences over the retina's surface. During the past 2 decades, imaging of small optical signals has been a powerful tool for high-resolution functional mapping in the neocortex. In this article, this technology is applied to the retina and demonstrates a general tool for noninvasively probing retinal function in many modalities. Imaging functional changes before anatomic consequences arise holds promise as a powerful tool for early diagnosis and treatment of retinal disease.

Adult↗