An uncle starts believing all your sarcastic comments. Or a kindhearted friend never understands anymore how you feel. These people may not just be momentarily off. Recent research indicates they may be exhibiting early signals that something is going awry in their brains.

Changes in social behavior, such as difficulty detecting insincere comments or feeling empathy, can be a window into our neurological health, scientists say. That is because how we interact with other people is one of the more complex functions the brain must perform. It requires a symphony of neurons firing throughout the brain and working together in networks so that we can detect, decode and interpret social signals. Deterioration in social functioning can begin even while executive functions like planning and organizing remain intact during the early stages of mental disorders.

Recognizing social changes that previously might have been shrugged off could allow for earlier diagnosis of a disorder and treatment, doctors say. It also could give families more time to prepare for long-term care.

With some childhood conditions, like autism or attention-deficit hyperactivity disorder, social problems are one of the primary characteristics of the disorder. In other conditions in which social problems aren't the main symptoms, including dementia, depression and schizophrenia, early clues may come from changes to a person's normal personality, such as becoming less friendly, understanding or attentive, or more paranoid.

'Whenever we see someone with an emotional or social symptom we always say, 'What's going on in the brain?'' says Katherine Rankin, a neurology professor at the University of California, San Francisco. Dr. Rankin and other scientists at UCSF, Stanford University and other institutions are studying the underlying neurobiology of social behavior. They are seeking to understand how these neural networks functionnormally and how changes in the anatomical structures and functioning can shed light on the progression of disease.

Social peculiarities can be subtle or drastic, ranging from a lack of interest in spending time with other people to problems reading social etiquette and emotionally inappropriate behaviors. Other social deficits that could signal a problem include the inabilities to focus attention on what other people are noticing or to imagine what another person is thinking.

Researchers believe there are several networks made up of different brain parts communicating with one another that are critical to social behavior. Some networks act as emotional brakes and others as the gas. Everyone has a different balance of these networks, which contributes to our personalities, emotions and behaviors. But with disease, the parts of the brain or how they communicate with other areas can be dramatically disrupted.

People are unlikely to observe social changes in themselves. So it is often up to family members to report their concerns to a doctor, says Dr. Rankin. She recommends people over the age of 40 or 50 see a neurologist if they experience changes in social or emotional functioning, or language or memory problems. An evaluation for an adult might include a physical examination, questions about changes in mood and activity levels, and assessments of cognitive functioning. For a child, there may also be questions about developmental milestones.

Dr. Rankin says the family of an older man she treated recently brought him in for an evaluation after watching him eat. During meals, the man would finish all the food on his plate, then pick it up and begin licking. It turned out the man had frontotemporal dementia, damage to the frontal lobe of the brain, for which he is now taking medication to treat symptoms, she says.

One critical brain pathway is called the ventral-salience network, which filters incoming information for that which is personally important. The network appears to be significant in helping determine people's emotional awareness. It also helps them evaluate the potential for social punishment. Then, the task-control network tells the brain to pay attention to the important information and to process it. The semantic-appraisal network adds our emotionalinterpretation to the situation. Together, these networks and others help us understand the context for social or emotional situations, say researchers.

When one or more of the networks go awry, we often lose the ability to empathize, which is one of the most complex social behaviors, says Dr. Rankin, who treats and studies dementia patients. To truly empathize, we need to correctly read meaningful emotional information and to figure out what an appropriateresponse is, which sometimes might not match what the other person is feeling, she says.

People with autism and schizophrenia tend to have difficulty with empathy. Stanford University researchers have suggested that a lack of response to emotionally meaningful information in the insula, a brain region at the hub of the salience network, can lead to a cascade of effects that result in inappropriate emotional displays.

Lucina Uddin, a cognitive neuroscientist at Stanford, and her colleagues are now studying whether brain imaging of this network can serve as a biological marker of autism in kids. 'The answer looks like yes,' says Dr. Uddin, who plans to publish the research soon.

The salience detection network also may go awry in anxiety, schizophrenia and other conditions, says Dr. Uddin. In anxiety, too much environmental stimuli registers in the brain as important and thus becomes overwhelming. People with schizophrenia may have difficulty figuring out what to attend to.

The ability to detect and understand insincerity is another basic social deficit that can occur with disease. In a study published last year in the journal Cortex, Dr. Rankin and her colleagues studied the ability to detect sarcasm in 102 patients who had been diagnosed with four progressive diseases that lead to memory loss: frontotemporal dementia, Alzheimer's disease, progressive supranuclear palsy and vascular-cognitive impairment. They compared the results with those of 77 healthy older people. Detecting such insincere forms of communication require many brain functions, including the ability to read emotion, see the world from another person's perspective and understand others' intentions.

In the study, participants viewed 16 videos in which they watched clips of people interacting in which some lied and others were sarcastic. All participants were able to understand sincere comments, but patients with frontotemporal dementia had trouble understanding lies and sarcasm. The other patients' ability to understand depended on the severity of their disease.

Bradford Dickerson, a neurology professor at Harvard Medical School, and colleagues have shown in studies that the size of certain parts of the brain important to emotional processing is associated with how many friends we have. 'More connected individuals might be better equipped to perceive social cues like facial expression' and might derive more positive experience from social interaction, writes Dr. Dickerson in a recent paper.