 Welcome to part two of the brain's inner workings. Here we explore the neurobiological basis of higher brain function. Previously we examined how individual brain cells communicate through specialized connections called synapses. Now we can begin the fascinating look into how groups of neurons work together. Interconnected groups of neurons in the brain are responsible for higher order thinking and complex behavior. Through investigating the brain on the chemical, functional and anatomical level, scientists unravel the vast power of the brain and health as well as disease. Neurotransmitters are chemicals that give rise to our everyday life, our actions, our moods, and our behaviors. The chemicals pass from neuron to neuron via synapses. Within the synapse, the glucose metabolism of the mitochondria and the electrical impulse of the action potential cause the vacuoles to intersect with the cellular wall and release neurotransmitters between junction membranes. Different functions and behaviors are localized in certain brain regions. Using this knowledge, the brain's many different mental functions can be broken down into more easily approachable elements. By looking at these smaller parts of brain regions and activities, a more comprehensive understanding of overall brain function can be built. For example, the circuits involved in vision receive information from the retina. After initial processing, these circuits analyze information in different streams so that there's one stream of information describing what the visual object is and another stream is concerned with where the object is in space. Once function is understood in the less complicated elements of brain organization, then this information can be reassembled to help understand the workings of the whole brain. Laboratory rats guide researchers to form a better understanding of complicated brain processes. For example, studying the rat within a maze helps uncover general principles about learning that can be applied to many species, including humans. Rats are good at remembering where things are and how to get them. Here the rat has learned how to find a tasty treat each time he walks around the triangular maze. But there's a catch. He has to turn in the maze in the opposite direction from the last try in order to get his treat. First left, then right, then left, then right. Using sophisticated techniques, it's possible to listen to the sounds of groups of brain cells firing before the rat makes his left-right decisions. Listen to how the neurons fire very quickly just before he makes his turns. That is the sound of his brain cells remembering where the treat is and where to get it. The lessons learned from the rat can be used to understand a similar process in the human brain. To do that, scientists can use technologies developed in recent decades such as functional magnetic resonance imaging, or fMRI. This allows the imaging of functional activity in the living brain. The fMRI machine makes it possible to take pictures of activity within a living brain. This is not a picture of the neurons or pathways, but instead it's an image of the activity occurring among those neurons and pathways. This is an indirect approach as it uses a marker for neuronal firing. In this case, it detects blood flow and blood oxygenation to provide maps of brain activity. We can see the localized increases in blood flow as the brain capillaries expand in size. Blood flows more rapidly through a larger tube. This increase can be used to map brain activity in response to specific tasks and stimuli, like remembering. As with all other organs, the brain is subject to malfunction. Complex problems like understanding depression and schizophrenia can now be addressed using these and other techniques. Here's an example of the kind of information we get when comparing the brains of normal and mentally ill people. The image on the left is from a normal subject. On the right is a schizophrenia patient where we can see the vast differences in the amount and location of brain activity. Clearly, several systems including higher cognitive processes, hearing and movement, are impacted in this disease. Imaging provides a way to identify how the brain processes information differently in schizophrenia. As scientists are learning more about brain circuitry, they are learning more about which circuits are involved with specific tasks. This makes it possible to compare brain regions in healthy people and people with mental illnesses. However, mental disorders are very complicated and still not well understood. These disorders affect our most complex brain processes like thinking, mood and behavior. There are several factors that contribute to mental illnesses including environmental conditions, social events, genetics and large chemical imbalances. What is clear is that mental illnesses are as devastating as any physical illness. Ultimately, basic and clinical research will unlock the mysteries of mental illnesses.