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- K. J. Friston
- 1996

Statistical parametric maps are spatially extended statistical processes that are used to test hypotheses about regionally specific effects in neuroimaging data. The most established sorts of statistical parametric maps (e.g. Friston et al 1991, Worsley et al 1992) are based on linear models, for example ANCOVA, correlation coefficients and t tests. In the… (More)

- J Ashburner, K J Friston
- NeuroImage
- 2000

At its simplest, voxel-based morphometry (VBM) involves a voxel-wise comparison of the local concentration of gray matter between two groups of subjects. The procedure is relatively straightforward and involves spatially normalizing high-resolution images from all the subjects in the study into the same stereotactic space. This is followed by segmenting the… (More)

- K J Worsley, S Marrett, P Neelin, A C Vandal, K J Friston, A C Evans
- Human brain mapping
- 1996

We present a unified statistical theory for assessing the significance of apparent signal observed in noisy difference images. The results are usable in a wide range of applications, including fMRI, but are discussed with particular reference to PET images which represent changes in cerebral blood flow elicited by a specific cognitive or sensorimotor task.… (More)

- C D Good, I S Johnsrude, J Ashburner, R N Henson, K J Friston, R S Frackowiak
- NeuroImage
- 2001

Voxel-based-morphometry (VBM) is a whole-brain, unbiased technique for characterizing regional cerebral volume and tissue concentration differences in structural magnetic resonance images. We describe an optimized method of VBM to examine the effects of age on grey and white matter and CSF in 465 normal adults. Global grey matter volume decreased linearly… (More)

- Karl J Friston
- 1994

1. INTRODUCTION This chapter is about making regionally specific inferences in neuroimaging. These inferences may be about differences expressed when comparing one group of subjects to another or, within subjects, over a sequence of observations. They may pertain to structural differences (e.g. in voxel-based morphometry-Ashburner and Friston 2000) or… (More)

In this paper we introduce the idea of explaining responses, in one cortical area, in terms of an interaction between the influence of another area and some experimental (sensory or task-related) parameter. We refer to these effects as psychophysiological interactions and relate them to interactions based solely on experimental factors (i.e., psychological… (More)

- K J Friston, K J Worsley, R S Frackowiak, J C Mazziotta, A C Evans
- Human brain mapping
- 1994

Current approaches to detecting significantly activated regions of cerebral tissue use statistical parametric maps, which are thresholded to render the probability of one or more activated regions of one voxel, or larger, suitably small (e. g., 0.05). We present an approximate analysis giving the probability that one or more activated regions of a specified… (More)

- Karl Friston
- Philosophical transactions of the Royal Society…
- 2005

This article concerns the nature of evoked brain responses and the principles underlying their generation. We start with the premise that the sensory brain has evolved to represent or infer the causes of changes in its sensory inputs. The problem of inference is well formulated in statistical terms. The statistical fundaments of inference may therefore… (More)

- K J Friston, L Harrison, W Penny
- NeuroImage
- 2003

In this paper we present an approach to the identification of nonlinear input-state-output systems. By using a bilinear approximation to the dynamics of interactions among states, the parameters of the implicit causal model reduce to three sets. These comprise (1) parameters that mediate the influence of extrinsic inputs on the states, (2) parameters that… (More)

- K J Friston, A P Holmes, +4 authors R Turner
- NeuroImage
- 1995

This paper presents a general approach to the analysis of functional MRI time-series from one or more subjects. The approach is predicated on an extension of the general linear model that allows for correlations between error terms due to physiological noise or correlations that ensue after temporal smoothing. This extension uses the effective degrees of… (More)