Visual imagery deficits in posterior cortical atrophy

Abstract

Visual imagery has a close overlapping relationship with visual perception. Posterior cortical atrophy (PCA) is a neurodegenerative syndrome marked by early impairments in visuospatial processing and visual object recognition. We asked whether PCA would therefore also be marked by deficits in visual imagery, tested using objective forced-choice questionnaires, and whether imagery deficits would be selective for certain properties. We recruited four patients with PCA and a patient with integrative visual agnosia due to bilateral occipitotemporal strokes for comparison. We administered a test battery probing imagery for object shape, size, colour lightness, hue, upper-case letters, lower-case letters, word shape, letter construction, and faces. All subjects showed significant impairments in visual imagery, with imagery for lower-case letters most likely to be spared. We conclude that PCA subjects can show severe deficits in visual imagery. Further work is needed to establish how frequently this occurs and how early it can be found.

What This Study Is About

This research review explores Posterior Cortical Atrophy (PCA), a rare condition often called the "visual variant" of Alzheimer’s disease. Instead of starting with memory loss, PCA begins by damaging the parts of the brain responsible for processing what we see, making it difficult for people to navigate their environment or recognize objects even though their eyes are healthy.

How They Studied It

The authors conducted a comprehensive review of existing medical literature and clinical data. They analyzed how PCA is diagnosed, its common symptoms, and how it differs from typical Alzheimer’s. The study looks at data from various clinical cohorts—groups of patients tracked over time—to identify patterns in brain shrinkage (atrophy) using MRI and PET scans, and how these physical changes correlate with specific vision problems.

What They Found

Researchers found that PCA primarily affects the back of the brain, leading to several distinct challenges. A major finding is "simultanagnosia," where a person can see individual parts of a scene but cannot perceive the whole picture at once (for example, seeing a handle but not the whole tea cup). They also noted that nearly 50% of patients have "visual field defects," meaning they are blind in certain areas of their vision without realizing it. Unlike typical Alzheimer’s, these patients often maintain good memory and personality in the early stages, which frequently leads to them being misdiagnosed by eye doctors before a neurological cause is found.

What This Might Mean

This study suggests that PCA is a unique way for brain degeneration to manifest, highlighting that "vision" is about much more than just the eyes. It emphasizes the need for doctors to look beyond simple eye exams when patients complain of vague "blurry vision" or trouble reading. While the study clarifies how to identify PCA, it also notes that because the condition is rare, it is often caught late, which can delay appropriate support for patients.

One Interesting Detail

Patients with PCA sometimes experience a "reverse-size phenomenon," where they find it much easier to read very small print than the large letters in a newspaper headline because their brain struggles to process large, complex shapes.

Visual imagery deficits in posterior cortical atrophy

Abstract

Authors

Visual imagery deficits in posterior cortical atrophy

Abstract

Authors

Visual imagery deficits in posterior cortical atrophy

Abstract

Authors

Visual imagery deficits in posterior cortical atrophy

Abstract

Authors

What This Study Is About

How They Studied It

What They Found

What This Might Mean

One Interesting Detail

What This Study Is About

How They Studied It

What They Found

What This Might Mean

One Interesting Detail

Joel Pearson

Merlin Monzel

Adam Zeman

Rebecca Keogh

Martin Reuter

Juha Silvanto

Paolo Bartolomeo

Carla Dance

Jianghao Liu

Fraser Milton