Anxiety is, generally speaking, a feeling of fear, tension and apprehension. It is completely normal to experience anxiety based on an actual threat, but people who experience extreme fear that is not proportionate to a threat may have clinical anxiety. Anxiety can present itself in many forms including panic disorder, obsessive compulsive disorder, generalized anxiety disorder, post-traumatic stress disorder and social anxiety. Anxiety has many potential causes--including genetics, environment and stress--and it affects several parts of the brain at once, according to the Mayo Clinic.
Neurotransmitters
While not all of the factors contributing to anxiety are understood, the Mayo Clinic asserts that malfunctions in certain neurotransmitters are likely involved. These include disruptions of naturally occurring brain neurotransmitters like dopamine, nor-epinephrine, serotonin and GABA. In some cases, the brain may not produce enough of a certain neurotransmitter; in other cases the brain's reuptake of the neurotransmitter may be overactive. The discovery that selective serotonin reuptake inhibitors (SSRIs) are useful in treating mood and anxiety disorders led to the hypothesis that serotonin is an especially important factor in anxiety, according to The Franklin Institute.
The Limbic System
The forebrain is the area most affected in people with anxiety disorders, according to The Franklin Institute. This limbic system located there is important in memory storage and creating emotions. This system is thought to process anxiety-related input and assess the severity of threats.
The Hippocampus
The hippocampus and amygdala are likely involved in anxiety as they as they are interconnected to both subcortical and cortical nuclei, according to The Franklin Institute. People with post-traumatic stress disorder sometimes exhibit a smaller hippocampus on brain scans. It's possible that due to stress there is a degeneration of dendrites in this region.
The Hypothalamus
The hypothalamus, which is important in controlling emotion, may also play a part in anxiety disorders. In patients with panic disorder, the hypothalamus, as well as other parts of the brain, display hyperactive neurotransmitter circuits. The autonomic nervous system, through connections with the locus coeruleus and hypothalamus, are meant to calm the panic response, according to CNS Forum.
The Basil Nuclei
Patients who suffer from obsessive-compulsive disorder often show increased activity in the basal nuclei and other areas of the forebrain, according to The Franklin Institute. Increased activity in the basal ganglia is also seen in patients with generalized anxiety disorder (GAD) during "vigilance" tasks, according to CNS Forum, and this suggests various hyperactive brain circuits in relation to GAD.
