The work of our group seeks to explain perceptual decision-making from the level of single brain cells through to mental states. We aim to understand the neuronal code underlying conscious processes. The problem is that neuronal activity sometimes represents processes of which we are aware and sometimes codes for information to which we have no access (Krug et al 2004). By using bistable images that have two or more perceptual interpretations, we study the mechanics of how simple decisions about visual appearance (Parker & Krug 2003). The activity of neurons in visual cortex does not just code for physical parameters of the stimulus, like direction of motion or visual depth, but also ultimately signals the percept of these stimuli. We have identified a strong cognitive signal in the activity of single V5/MT neurons that may drive the perceptual decisions about such an ambiguous figure (Dodd et al 2001; Krug 2004).

Current Research Programme

Neuronal mechanisms in V5/MT by which cognitive signals influence visual perception.

The link between brain activity and perceptual decisions described above is ultimately only a correlation. In order to unravel the brain mechanisms of decision-making, we need to identify causal interactions between neuronal activity and behaviour. One important tool to establish causal relationships between activity in a group of neurons and decision-making is electrical micro-stimulation. By electrically stimulating small groups of neurons, we can intervene in a predictable and measured way in perceptual decision-making (Krug et al 2005, Soc Neurosci Abs 621.2). Thus, we can identify and manipulate different stages in the decision-making process.

(i) The underlying neuronal connectivity.

Neuronal signals in V5/MT correlate with perceptual switches in bistable structure-from-motion figures (Bradley et al., 1998; Dodd et al. 2001). Different studies, psychophysics and neuronal have postulated that specific intrinsic connectivity in V5/MT underlies the emergence of such signals (Bradley et al., 1998; Nawrot & Blake 1991). We are currently investigating the nature and specificity of intrinsic connections between columns in V5/MT.

(ii) How neuronal mechanisms support the emergence of different mental states.

Perceptual decision-making can also be affected in humans by mental illness. In collaborative projects with different groups at the Warneford hospital and the University of Bristol, we are currently studying perceptual decision-making in subjects with bipolar disorder or autism (Brunskill et al., Neurosci Abs. 2003; Krug et al.,2007).  In the future, we would like to extend this work by studying decision-making while pharmacological agents are applied to identified groups of neurons. Thus, we hope to mimic the specific deficits in the human patients.

Kristine Krug