Related Experiment Video
Updated: May 9, 2026
07:11
Functional Magnetic Resonance Imaging (fMRI) of the Visual Cortex with Wide-View Retinotopic Stimulation
Published on: December 8, 2023
Structural and functional changes across the visual cortex of a patient with visual form agnosia
Holly Bridge1, Owen M Thomas, Loredana Minini
1Functional MRI of the Brain Centre, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.
Summary
Visual-form agnosia impairs object recognition but not visually guided actions. This study uses MRI to reveal structural and functional brain changes in patient DF, highlighting preserved visual pathways for action.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Neuroimaging
Background:
- Visual-form agnosia is characterized by a loss of shape recognition, yet visually guided actions remain intact.
- This dissociation supports the dual visual systems hypothesis: one for perception and one for action.
- Patient DF exhibits persistent visual-form agnosia following carbon monoxide exposure.
Purpose of the Study:
- To investigate the structural and functional brain changes in patient DF using high-resolution MRI.
- To quantify cortical thickness changes in the occipital cortex.
- To correlate structural damage with functional activity and preserved visual abilities.
Main Methods:
- High-resolution structural and functional Magnetic Resonance Imaging (MRI) of the brain.
- Quantification of cortical thickness, particularly in the occipital cortex.
- Topographic mapping of visual areas (V1, V2, V3, hV4) to assess retinotopic order.
- Assessment of white matter connections.
Main Results:
- Significant cortical thinning was observed in the lateral occipital cortex (LOC), a key area for object recognition.
- Reduced white matter connectivity between LOC and other brain regions was identified.
- Despite structural damage, functional imaging revealed surviving activity in some damaged areas.
- Ordered retinotopic maps were present in ventral visual areas (V1-V4) but not consistently in dorsal V2 and V3.
- Preserved visual pathways supporting visually guided actions were highlighted.
Conclusions:
- Understanding visual-form agnosia requires integrating both structural and functional neuroimaging data.
- DF's case demonstrates specific cortical alterations underlying the perception-action dissociation.
- The study identifies critical cortical routes enabling visually guided actions despite severe object recognition deficits.
Related Concept Videos
01:12Visual Agnosia
Visual agnosia is a condition characterized by the inability to recognize visually presented objects despite having normal vision. For instance, a person with visual agnosia can describe the shape and color of an object but cannot identify or name it. This impairment does not affect their visual field, acuity, color vision, brightness discrimination, language, or memory. An example of this condition in a social setting is someone at a dinner party asking for "that silver thing with a round end"...
01:24Prosopagnosia
Prosopagnosia, also known as face blindness, is the inability to recognize faces. In severe cases, individuals with prosopagnosia may not recognize close family members, including parents and spouses, by their faces. For instance, someone with prosopagnosia might walk past their child in a crowd, only realizing their mistake upon noticing their child's distinctive backpack or favorite jacket. Prosopagnosia specifically impairs facial recognition, while the recognition of other objects or...
01:21Association Areas of the Cortex
Association areas are regions of the cerebral cortex that do not have a specific sensory or motor function. Instead, they integrate and interpret information from various sources to enable higher cognitive processes such as memory, learning, and decision-making. Some key association areas include the following:
Prefrontal Association Area: This area is located in the frontal lobe and is involved in planning, decision-making, and moderating social behavior. It connects with primary motor areas,...
Prefrontal Association Area: This area is located in the frontal lobe and is involved in planning, decision-making, and moderating social behavior. It connects with primary motor areas,...
01:24Vision
Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.
01:22Photoreceptors and Visual Pathways
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
01:26Visual System
Light enters the eye through the cornea, a transparent, dome-shaped surface covering the surface of the eyeball that helps to direct and focus incoming light. This light is then channeled toward the pupil, an adjustable opening whose size is controlled by the iris. The iris, a pigmented muscle, regulates the amount of light entering the eye by contracting or dilating the pupil, thereby ensuring optimal light levels for clear vision.
Once through the pupil, the light passes through the lens, a...
Once through the pupil, the light passes through the lens, a...