High resolution human brain atlas

This project aims to create a high resolution atlas of the human brain. We are using 7T MRI and multiple sequences to gather hundreds of images of the living human brain.

A BOLD approach to natural scene statistics

Given the vast diversity of natural scenes, which can range from a sparse desert to dense foliage, it is not immediately obvious what property the visual system may have become tuned to. However, in the last few decades, many statistical properties have been discovered across natural scenes which may have been exploited by the visual system throughout evolution.

One such property is the 1/f a amplitude spectrum which describes a distribution of luminance intensities across spatial and temporal scales (i.e. pixels close to each other in space and time are more likely to have similar intensity values compared to pixels further away from each other). This property is also considered to underlie the scale-invariant, fractal properties of natural scenes (i.e. the branching pattern of a tree is self-similar from the largest branch to the smallest twig).

Research has been conducted in an attempt to determine the extent in which the visual system is tuned to such properties. However, at present, most of this work has been conducted at the behavioural level using psychophysics, while little has been done at the cortical level.

For this project we use both psychophysics and fMRI to measure responses to highly controlled synthetic noise stimuli, which only differ in their 1/f a amplitude spectrum (manipulation of a) or their fractal dimension (fractal D). By measuring discrimination sensitivity and BOLD activity, we aim to better understand the degree in which behaviour matches activity in early visual cortex toward the 1/f a amplitude spectrum and its underlying fractal properties.

Vascular effects on the BOLD response

Venous contributions to the BOLD signal in fMRI are currently not completely understood.

This project uses fMRI to elucidate the retinotopic organisation of human V4 (hV4) after decades of experiment and debate. The prevalence of apparently 'incomplete' maps of hV4 has yet to be thoroughly explained however, it is likely that a variety of factors contribute to difficulty in accurately mapping this region, in particular artefact from nearby veins.

We use a combination of novel techniques to examine and correct retinotopic maps of hV4, including depth-dependent fMRI, susceptibility artefact correction and inverted voxel correction.

Correcting susceptibility artefacts in fMRI

In this project we try to correct the susceptibility artefact in fMRI images, especially in high-resolution images in which the distortions are severe. We developed a susceptibility artefact method by using a T1w anatomy image and two fMRI images acquired using the identical sequences but with opposite polarities of the phase-encoding gradient.

The proposed method is called anatomy-guided inverse-gradient susceptibility artefact (AISAC). The proposed AISAC method was demonstrated that it is more robust, less blurred and run faster than the existing susceptibility artefact.

The interaction of function and anatomy in early visual cortex

The tuning of the visual system to the movement of natural scenes

How is the visual system tuned to the movement of natural scenes? It has been robustly observed that visual sensitivity is optimal when still images share similar statistical properties to those that exist in natural scenes. What underlying features drive this sensitivity?

This project aims to demonstrate the sensitivity of the visual system to stimuli that approximate natural movement and understand which structural properties inherent in moving, natural images play a key role in visual perception.

The sensitivity of echo-planar imaging to magnetic field inhomogeneities

Magnetic field inhomogeneities are common in the pre-frontal cortex due to differences in magnetic susceptibility between air-filled cavities and tissue/bone in the front of the human head.

Due to individual differences in sinus anatomy and relative position to the pre-frontal cortex, artefact correction must be performed on a subject-to-subject basis. This project aims to test the efficacy of the Anatomy-guided Inverse Gradient Susceptibility Artefact Correction method in pre-frontal cortex.