CiteULike: Group: Glimcher_Lab - with tag bold

Spatial specificity of BOLD versus cerebral blood volume fMRI for mapping cortical organization

Stelios Smirnakis — 2007-05-28T13:47:29-00:00

J Cereb Blood Flow Metab, Vol. 27, No. 6. (10 January 2007), pp. 1248-1261.

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

Andreas Tolias — 2006-06-08T15:45:09-00:00

Neuron, Vol. 48, No. 6. (22 December 2005), pp. 901-911.

SummaryOver 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.

The underpinnings of the BOLD functional magnetic resonance imaging signal.

NK Logothetis — 2006-05-23T15:07:15-00:00

J Neurosci, Vol. 23, No. 10. (15 May 2003), pp. 3963-3971.

Neurophysiological investigation of the basis of the fMRI signal.

NK Logothetis — 2005-09-29T20:08:57-00:00

Nature, Vol. 412, No. 6843. (12 July 2001), pp. 150-157.

Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trial-by-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.