In this lesson, students will observe and count planaria (flatworms) movements with and without the addition of a plant extract. Plants and herbs have been used around the world for millennia to alter brain function; in most places, plants are used daily to alter mental function. For example, coffee and black tea help people to wake up in the morning and chamomile tea helps people to relax in the evening. Some people regularly use alcohol, nicotine, and illegal drugs such as cocaine; these drugs are derived from plants and have large effects on the human nervous system. Students will explore how plant extracts act as stimulants or depressants and affect planaria movement. Planaria are a widely used model organism.