Amalia Papanikolaou

My PhD research has mainly focused on the ability of the visual cortex to reorganize following injury of the visual pathways. Damage to the primary visual cortex (V1) or its postchiasmatic inputs as a result of stroke or other brain diseases can lead to a loss of conscious vision in the contralateral visual hemifield. There are currently no widely accepted treatment options available for people with visual cortical damage. Understanding brain repair processes is an important step in the effort to design treatments aimed at enhancing the ability of the nervous system to recover after injury. In attempting to achieve this, it is important to study in detail how the adult human brain reorganizes after injury.

We propose to perform a systematic study of visual cortical plasticity in a cohort of adult human patients with carefully selected cortical pathology like stroke,

This will be done by: 1) Mapping changes in human visual cortex organization using functional magnetic imaging (fMRI) and comparing both with the intact hemispheres in the same patients and with control subjects without lesion and 2) Determine whether rehabilitative training increases the degree of cortical reorganization.

Personal website:

Population receptive field mapping in human subjects with visual cortical lesions.

Introduction

Damage to the primary visual cortex (V1) as a result of stroke typically leads to the inability to perceive visual stimuli in the affected region of the contralateral visual hemifield (scotoma). However, in spite of this, several higher visual areas have been shown to be modulated by visual stimuli presented inside the scotoma. A much debated issue is whether adult visual cortex is able to reorganize after injury, and if so, what is the extent and the mechanism of the observed reorganization.

Goals

We propose to perform a systematic study of visual cortical plasticity in a cohort of adult human patients with carefully selected cortical pathology like stroke. This will be done by: 1) Mapping changes in human visual cortex organization and comparing both with the intact hemispheres in the same patients and with control subjects without lesion. 2) Determine whether rehabilitative training increases the degree of cortical reorganization.

Methods

We have used functional magnetic resonance imaging (fMRI) methods to study visual cortex reorganization after injury in adult human subjects. To this end we applied a method introduced by Dumoulin and Wandell [1],  which uses functional magnetic resonance imaging (fMRI) to measure the aggregate receptive field properties of neuronal populations voxel by voxel in the visual cortex. FMRI measurements were obtained during the presentation of a moving bar stimulus which traversed the visual field while the subjects were fixating and these measurements were used to derive an estimate of the voxel based population receptive field center and radius. We studied several subjects with quadrandanopsia and hemianopsia resulting from  cortical lesions and compared them to the range of measurements obtained from a group of  normal controls.

Initial results and conclusions

There appear to be no significant retinotopic map alteration in the early visual areas of patients suffering from V1 lesions. However, there is a change in the distribution of receptive field centers in higher visual areas like hV5/MT+. This may in part reflect the fact that some of the input to hV5/MT+ receptive fields has been lost with the V1+ lesion, but is also suggesting that they receive contributions from a V1 bypassing pathway which could be enhanced after training. Gathering information about the role that specific networks of brain areas play in cortical reorganization and recovery following injury will allow us to generate concrete hypotheses about how modulating the activity of these networks may enhance recovery.

References

1.      Dumoulin, S.O., Wandell, B.A. (2008). Population receptive field estimates in human visual cortex, Neuroimage 39.

Supervisor

Prof. Stelios Smirnakis

Collaborators

Dr. Georgios Keliris

Yibin Shao