Visually Driven Activation in Macaque Areas V2 and V3 without Input from the Primary Visual Cortex

Creating focal lesions in primary visual cortex (V1) provides an opportunity to study the role of extra-geniculo-striate pathways for activating extrastriate visual cortex. Previous studies have shown that more than 95% of neurons in macaque area V2 and V3 stop firing after reversibly cooling V1 [1], [2], [3]. However, no studies on long term recovery in areas V2, V3 following permanent V1 lesions have been reported in the macaque. Here we use macaque fMRI to study area V2, V3 activity patterns from 1 to 22 months after lesioning area V1. We find that visually driven BOLD responses persist inside the V1-lesion projection zones (LPZ) of areas V2 and V3, but are reduced in strength by ∼70%, on average, compared to pre-lesion levels. Monitoring the LPZ activity over time starting one month following the V1 lesion did not reveal systematic changes in BOLD signal amplitude. Surprisingly, the retinotopic organization inside the LPZ of areas V2, V3 remained similar to that of the non-lesioned hemisphere, suggesting that LPZ activation in V2, V3 is not the result of input arising from nearby (non-lesioned) V1 cortex. Electrophysiology recordings of multi-unit activity corroborated the BOLD observations: visually driven multi-unit responses could be elicited inside the V2 LPZ, even when the visual stimulus was entirely contained within the scotoma induced by the V1 lesion. Restricting the stimulus to the intact visual hemi-field produced no significant BOLD modulation inside the V2, V3 LPZs. We conclude that the observed activity patterns are largely mediated by parallel, V1-bypassing, subcortical pathways that can activate areas V2 and V3 in the absence of V1 input. Such pathways may contribute to the behavioral phenomenon of blindsight

Praezise 'near-online' Bestimmung in der Landesvermessung mit Hilfe eines Netzes permanent messender GPS-Empfaenger auf Referenzstationen Schlussbericht HPPS. Hochpraeziser Permanenter Positionierungs-Service

Available from TIB Hannover: F96B1951+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Deutsche Agentur fuer Raumfahrtangelegenheiten (DARA) GmbH, Bonn (Germany)DEGerman

Mapping Cortical Activity Elicited with Electrical Microstimulation Using fMRI in the Macaque

Over the last two centuries, electrical microstimulation has been used to demonstrate causal links between neural activity and specific behaviors and cognitive functions. However, to establish these links it is imperative to characterize the cortical activity patterns that are elicited by stimulation locally around the electrode and in other functionally connected areas. We have developed a technique to record brain activity using the blood oxygen level dependent (BOLD) signal while applying electrical microstimulation to the primate brain. We find that the spread of activity around the electrode tip in macaque area V1 was larger than expected from calculations based on passive spread of current and therefore may reflect functional spread by way of horizontal connections. Consistent with this functional transynaptic spread we also obtained activation in expected projection sites in extrastriate visual areas, demonstrating the utility of our technique in uncovering in vivo functional connectivity maps

Macaque visual cortex reorganisation after homonymous retinal scotoma probed by fMRI

Visual cortex has the capacity to reorganize in response to changes in sensory input. Early studies of visual deprivation (Blakemore, Hubel, LeVay) suggested that stimulus driven reorganization occurs only during a critical period in early development. Recent electrophysiological studies (Gilbert, Kaas, Chino, Rosa, Heinen) suggest that the visual system of adult mammals may undergo significant reorganization after de-afferentiation. There is an ongoing debate regarding the nature and extent of this reorganization (Horton, DeAngelis). Here we describe measurements of cortical reorganization after inducing a 5-8o homonymous scotoma in the retinas of adult rhesus macaques with a photocoagulation laser (GYC-2000, NIDEK). We used 4.7T functional magnetic resonance imaging (fMRI) in the anesthetized macaque preparation (Logothetis et al., Nat Neurosci 1999) to track the changes in visual field maps in early cortical areas. FMRI is appealing as it is noninvasive, provides global coverage of the visual areas, and facilitates comparison with human studies. By comparing the activation patterns seen as a function of time after induction of the scotoma we aim to outline the temporal course of cortical reorganization. Preliminary results, based on one monkey, reveal a localized cortical region within V1 (~1.2x2.5cm2) whose signal response is strongly diminished by the lesion. Further, it appears that the fraction of area V1 silenced by the scotoma changes in time

Entwicklung von Algorithmen und Software fuer GNSS-Empfaenger neuester Technologie unter besonderer Beruecksichtigung von Echtzeitanwendungen und Sensorintegration (MultiNAV)

Available from TIB Hannover: F04B338 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman

Neuroscience: Rewiring the adult brain (Reply)

We disagree with Calford et al. that there is a consensus on adult plasticity in primate V1 cortex: for example, macaque area V1 cytochrome oxidase levels remained depressed for several months after binocular retinal lesions; no reorganization in macaque V1 after monocular retinal lesions was found; and no area V1 reorganization in a patient with macular degeneration was detected