They may be reaching out for interaction and connection with others. As the disease worsens, communication needs change. People may lose their ability to express themselves before they lose their ability to understand. Non-verbal communication will become more important as time passes. Pay attention to feelings.
Reminiscence can be very useful and validating - memories of the past remain intact longer.
Be aware of how your own behavior or emotions affect the person with dementia. Don't place unreasonable demands on the person. Don't expect them to regain lost skills - encourage remaining capabilities. Suspiciousness is often one of the symptoms of this disease. Reassurance and distraction may be helpful.