Summary: Researchers identified specific brain network connections associated with anosognosia, a condition where patients are unaware of their neurological or psychiatric deficits.
Using a technique called lesion network mapping, they identified separate networks linked to visual and motor anosognosia and a shared network responsible for awareness of these deficits. The shared network converged on the hippocampus and precuneus, both associated with memory.
This is the first systematic analysis to highlight the role of the hippocampus in visual anosognosia.
- Lesion network mapping was the key technique used by researchers to analyze the connectivity patterns of 267 lesion locations associated with vision loss or weakness (with and without awareness).
- Visual anosognosia, also known as Anton syndrome, involves complete cortical blindness and unawareness of this vision loss.
- The study identified the role of the hippocampus in visual anosognosia for the first time, suggesting that memory-associated structures are necessary to recognize a deficit by comparing current visual inputs to prior information stored in memory.
Source: Brigham and Women’s Hospital
Anosognosia is a condition in which a patient is unaware of their neurological deficit or psychiatric condition. Visual anosognosia, also called Anton syndrome, is associated with complete cortical blindness and unawareness of vision loss.
Researchers from Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system, sought to identify brain network connections associated with anosognosia.
The investigators analyzed the connectivity patterns of 267 lesion locations associated with either vision loss (with and without awareness) or weakness (with and without awareness).
Researchers used a recently validated technique termed lesion network mapping to test whether these lesion-induced deficits map to specific brain networks. They were able to identify distinct network connections associated with visual anosognosia and motor anosognosia as well as a shared network for awareness of these deficits.
The visual anosognosia network was defined by connectivity to visual and metacognitive processing regions while the shared network for awareness converged on the hippocampus and precuneus—brain structures that are associated with memory.
“Despite being described more than 100 years ago, visual anosognosia has had little formal analysis,” said corresponding author Isaiah Kletenik, MD, an investigator at Brigham’s Division of Cognitive and Behavioral Neurology and the Center for Brain Circuit Therapeutics.
“Our results are the first to identify the role of the hippocampus in a systematic analysis of visual anosognosia.
“Memory-associated structures are necessary to recognize a deficit by comparing visual inputs to prior information stored in memory while updating self-knowledge about performance compared to previous abilities.”
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Original Research: Closed access.
“Network Localization of Awareness in Visual and Motor Anosognosia” by Isaiah Kletenik et al. Annals of Neurology
Network Localization of Awareness in Visual and Motor Anosognosia
Unawareness of a deficit, anosognosia, can occur for visual or motor deficits and lends insight into awareness itself; however, lesions associated with anosognosia occur in many different brain locations.
We analyzed 267 lesion locations associated with either vision loss (with and without awareness) or weakness (with and without awareness). The network of brain regions connected to each lesion location was computed using resting-state functional connectivity from 1,000 healthy subjects. Both domain specific and cross-modal associations with awareness were identified.
The domain-specific network for visual anosognosia demonstrated connectivity to visual association cortex and posterior cingulate while motor anosognosia was defined by insula, supplementary motor area, and anterior cingulate connectivity. A cross-modal anosognosia network was defined by connectivity to the hippocampus and precuneus (false discovery rate p < 0.05).
Our results identify distinct network connections associated with visual and motor anosognosia and a shared, cross-modal network for awareness of deficits centered on memory-related brain structures.