Early effects of exposure-based cognitive behaviour therapy on the neural correlates of anxiety.

Exposure-based cognitive-behaviour therapy (CBT) for anxiety disorders is an effective intervention, but the brain mechanisms driving recovery are largely unknown. In this experimental medicine study, we investigated to what degree CBT affects neural markers of anxiety at an early stage of treatment, to identify dynamic mechanistic changes which might be crucial in the process of recovery as opposed to those seen following full treatment completion. In a randomised controlled trial, unmedicated patients with panic disorder either received four weekly sessions of exposure-based CBT (N = 14) or were allocated to a waiting group (N = 14).

Vestibular inputs to human motion-sensitive visual cortex.

Two crucial sources of information available to an organism when moving through an environment are visual and vestibular stimuli. Macaque cortical area MSTd processes visual motion, including cues to self-motion arising from optic flow and also receives information about self-motion from the vestibular system. In humans, whether human MST (hMST) receives vestibular afferents is unknown.

Spatial attention changes excitability of human visual cortex to direct stimulation.

Conscious perception depends not only on sensory input, but also on attention [1, 2]. Recent studies in monkeys [3-6] and humans [7-12] suggest that influences of spatial attention on visual awareness may reflect top-down influences on excitability of visual cortex. Here we tested this specifically, by providing direct input into human visual cortex via cortical transcranial magnetic stimulation (TMS) to produce illusory visual percepts, called phosphenes.

Chronostasis without voluntary action.

In a previous study we explored auditory chronostasis and suggested an arousal account of this temporal illusion rather than one dependent on backdating actions to the onset of a motor event. Here we present three experiments designed to distinguish between two competing accounts of the mechanisms underlying the illusion. Experiment 1 investigated whether voluntary movements are necessary for the illusion to occur.

Phosphene threshold as a function of contrast of external visual stimuli.

Transcranial magnetic stimulation (TMS) of the occipital lobe is frequently used to induce visual percepts by direct stimulation of visual cortex. The threshold magnetic field strength necessary to elicit a visual percept is often regarded as a measure of electrical excitability of visual cortex. Using single-pulse TMS during visual motion stimulus presentation, we investigated the relationship between different degrees of visual cortical preactivation and cortical phosphene threshold (PT).

The site of saccadic suppression.

During rapid eye movements, or saccades, stable vision is maintained by active reduction of visual sensitivity. The site of this saccadic suppression remains uncertain. Here we show that phosphenes--small illusory visual perceptions--induced by transcranial magnetic stimulation (TMS) to the human occipital cortex are immune to saccadic suppression, whereas phosphenes induced by retinal stimulation are not, thus providing direct physiological evidence that saccadic suppression occurs between the retina and the occipital visual cortex.

Perception of self-motion from peripheral optokinetic stimulation suppresses visual evoked responses to central stimuli.

In a previous functional neuroimaging study we found that early visual areas deactivated when a rotating optical flow stimulus elicited the illusion of self-motion (vection) compared with when it was perceived as a moving object. Here, we investigated whether electrical cortical responses to an independent central visual probe stimulus change as a function of whether optical flow stimulation in the periphery induces the illusion of self-motion or not. Visual-evoked potentials (VEPs) were obtained in response to pattern-reversals in the central visual field in the presence of a constant peripheral large-field optokinetic stimulus that rotated around the naso-occipital axis and induced intermittent sensations of vection.

Posture and mental task performance when viewing a moving visual field.

We investigated the characteristics of standing posture and performance of concurrent cognitive tasks in subjects confronted by whole field visual motion. Movements of the head and centre of pressure (COP) were recorded in 12 subjects who performed modified Brooks spatial and verbal tasks when in quiet stance viewing a chequerboard pattern, planar, visual field, moving with uniform velocity (25 degrees /s, 50 degrees /s and 76 degrees /s). Eight subjects were also tested seated to control for the effect of stance.

Auditory chronostasis: hanging on the telephone.

The perception of time can be illusory: we have all waited anxiously for important seconds to tick away slowly at the end of a football game and have experienced the truth of the adage "time flies when you're having fun." One illusion of time experience that has recently been investigated, the apparent slowing of the movement of the second hand on the clock when one first looks at it, has been termed "chronostasis," and it has been suggested that the effect is unique to vision and is dependent on eye movements. We sought to test whether the effect is really unique to vision or whether it can also be produced with auditory stimuli.

Neural correlates of visual-motion perception as object- or self-motion.

Both self-motion and objects moving in our visual field generate visual motion by displacing images on the retina. Resolving this ambiguity may seem effortless but large-field visual-motion stimuli can yield perceptual rivalry between the real percept of object-motion and the illusory percept of self-motion (vection). We used functional magnetic resonance imaging to record brain activity in human observers exposed to constant-velocity roll-motion.

Percept-related changes in horizontal optokinetic nystagmus at different body orientations in space.

Large-field motion of the visual environment is a powerful stimulus to induce the perception of contra-directional self-motion in a stationary observer. We investigated the interrelations between horizontal optokinetic nystagmus and subjective states of motion perception under variation of subjects' orientation with respect to gravity. Subjects were tested sitting upright and lying supine, and signalled transitions between object- and self-motion perception whilst viewing an optokinetic stimulus rotating about the subjects' longitudinal axis at a range of angular velocities.

Visual motion stimulation, but not visually induced perception of self-motion, biases the perceived direction of verticality.

Large-field torsional optokinetic stimulation is known to affect the perceived direction of gravity with verticality judgements deviating towards the direction of visual stimulus rotation. The present study aimed to replicate this effect and to examine it further by subjecting participants to optokinetic stimulation in roll, resulting in spontaneous alternations between the perception of object-motion and that of contradirectional self-motion (vection), as reported by the subjects. Simultaneously, subjects were oscillated laterally in a flight simulator and indicated their perception of postural verticality.

Vision: when the clock appears to stop.

Eye movements produce a temporary loss of visual sensitivity known as saccadic suppression, and a distortion of space perception known as saccadic compression. A new study has reported a seemingly related phenomenon --chronostasis---in which one's perception of time also undergoes an illusory distortion during rapid movements of the eyes.