Neuroscience: Cataloguing default mode network disruption in neurologic disorders

The default mode network, a network of brain regions primarily active during rest and involved in self-referential and introspective thought, has been found to be altered in various neurologic disorders. Understanding these changes has been crucial for both diagnosing and conceptualizing these disorders. Following are some specific neurologic disorders where alterations in the default mode network have been observed:

1. Alzheimer disease and other forms of dementia

• Decreased connectivity. Functional connectivity is reduced within the default mode network in Alzheimer disease, particularly between the posterior cingulate cortex and the medial prefrontal cortex. This disruption is thought to contribute to the cognitive and memory deficits characteristic of Alzheimer disease.
• Early biomarker. Changes in the default mode network can occur before the onset of clinical symptoms, making them a potential early biomarker for Alzheimer disease and other dementias.

2. Autism spectrum disorders

• Altered connectivity patterns. Individuals with autism spectrum disorder often show atypical connectivity within the default mode network. This can manifest as either hyperconnectivity or hypoconnectivity, depending on the individual and the specific regions of the default mode network examined.
• Relation to social deficits. These alterations in the default mode network have been linked to difficulties with social interaction and communication, core challenges in autism spectrum disorder.

3. Schizophrenia

• Disrupted default mode network activity. Schizophrenia is associated with disruptions in the default mode network, particularly reduced connectivity and activity. This disruption is believed to contribute to the characteristic symptoms of schizophrenia, such as impaired thought processes and a distorted sense of self.
• Link to hallucinations. Some studies suggest that hyperactivity in certain default mode network regions may be related to the auditory hallucinations experienced by some individuals with schizophrenia.

4. Major depressive disorder

• Increased default mode network activity. Increased activity and connectivity within the default mode network, especially in areas related to self-referential thought, are often observed in major depressive disorder. This is believed to be related to the rumination and excessive self-focus seen in depression.
• Connectivity with other networks. Altered connectivity between the default mode network and other brain networks, such as the affective network, has been observed in depression, possibly contributing to the dysregulation of mood and emotional responses.

5. Attention-deficit/hyperactivity disorder (ADHD)

• Reduced suppression of default mode network. In ADHD, there is often a failure to adequately suppress activity in the default mode network during task-focused activities. This lack of suppression may contribute to inattentiveness and difficulties in sustaining attention.

6. Traumatic brain injury and post-traumatic stress disorder

• Variable changes. Both traumatic brain injury and post-traumatic stress disorder can lead to changes in the default mode network, though these can vary widely among individuals. These changes are often associated with difficulties in cognitive function, emotional regulation, and memory.

7. Parkinson disease

• Connectivity changes. Parkinson disease, particularly as it progresses to involve cognitive impairment, has been associated with changes in the connectivity of the default mode network, which may be related to cognitive deficits seen in the disease.

Changes in the activity and connectivity of the default mode network can be both a cause and a consequence of various neurologic conditions. As neuroimaging techniques continue to advance, our understanding of these changes and their implications for diagnosis and treatment will likely become even more refined.

Related MedLink Neurology content: Neuroscience: Origins and relevance of the default mode network

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