Brain and Psychiatric Disorders

Major Depressive Disorder/Clinical Depression

Involve depression and/or anhedonia (inability to experience pleasure) lasting for more than 2 weeks

-Sleep disturbances, thoughts of suicide, difficulty meeting requirements of daily living (jobs, healthy diet, hygiene, social contact)

Types of MDD

1. Reactive Depression - Triggered by a negative experience

2. Endogenous Depression - Triggered by no apparent cause

Brain Differences in Depressive Disorders

Reduced grey matter of the prefrontal cortex, hippocampus, amygdala, and the cingulate cortex

-Reduced white matter within the frontal cortex

Also has atypical activity in frontal cortex, cingulate cortex, insular cortex, amygdala, thalamus, and the striatum

-Connectivity (communication) between brain regions are also altered

Theories of Depression

Monoamine Theory of Depression

Depressive Disorders arise as a result of reduced activity of the serotonin and norepinephrine (monoamines) synapses

-Explains the up-regulation of the serotonin and norepinephrine receptors in depressed individuals

Neuroplastic Theory of Depression

Depression arises as a result of a reduction in neurotrophin synthesis and neurogenesis in the hippocampus resulting in neuronal loss and neuropathology

-Since the effects of anti-depressant drugs only manifest after a few weeks, this means the drugs induce downstream changes that result in neuroplastic changes

-Anti-depressant drugs enhance neuroplastic processes, resulting in increases synthesis of neurotrophins and neurogenesis in the hippocampas

BDNF

Brain-Derived-Neurotrophic-Factor, reduced levels of BDNF serves as a biomarker for depression

-Anti-depressants increase BDNF which increases certain neuroplastic processes (neurogenesis, neurotrophin synthesis) that alleviates depression

Bipolar Disorders

Psychiatric disorder that involves alternating bouts of depression and hypomania/mania

-Hypomania involves a reduced need for sleep, high energy, and positive affect

-Mania is the extreme version of hypomania (delusions of grandeur, overconfidence, impulsivity, distractibility and psychosis)

Types of Bipolar Disorders

Type 1 - Involves depression and mania and hypomania, or just mania

Type 2 - Involves depression and ONLY hypomania

Brain Differences in Bipolar Disorders

Reduced grey matter in the medial prefrontal cortex, left anterior cingulate cortex, left superior temporal gyrus, certain regions of the prefrontal cortex and the hippocampus

-Along with atypical activation within the frontal lobe, medial temporal lobe structures, and the basal ganglia and atypical functional connectivity between some of them

Theories of Bipolar Disorders

1. Dysregulation of the hypothalamic pituitary adrenal axis

2. Disruption in the circadian rhythm

3. Changes in the neurotransmission of GABA, glutamate and dopamine

4. Low levels of BDNF

5. Reward-Hyper Sensitivity Theory of Depression

Reward Hyper Sensitivity Theory of Depression

Bipolar disorder results from a dysfunctional brain-reward system, reward system over-reacts to rewards or over-reacts to a lack of reward

-Repeatedly rewards individuals for their activities, leading to excessive goal seeking (hypomania or mania)

-As a result, when individuals fail to achieve the goal it leads to an excessive decrease in reward seeking (depression)

Increase in activity of the prefrontal/striatal reward circuits within depressive/manic states is evidence of the theory

Anxiety Disorders

Involve chronic fear in the absence of any direct threat, common psychological correlate of stress

-Anxiety can be adaptive if it motivates effective coping behaviours; when it disrupts functioning it becomes a disorder

Types of Anxiety Disorders

-All involve rapid heart rate, high blood pressure, nausea, breathing difficulties, sleep disturbances, a high levels of stress hormones (glucocorticoid hormones)

1. Generalized Anxiety Disorder - Extreme feelings of anxiety and worry about general life events

2. Specific Phobias - Strong Fear/anxiety over a specific object/situation

3. Agoraphobia - Fear of public places and open spaces, separate from phobias since it is more incapacitating than most phobias

4. Panic Disorder - Recurrent and rapid onset of extreme fear and severe symptoms of stress called Panic Attacks (choking, heart palpitations, shortness of breath)

• Panic Attacks can occur in cases of Generalized Anxiety Disorder, a specific phobias, and agoraphobia

Neural Basis of Anxiety Disorders

1. Deficits in GABAergic and Serotonergic transmission

2. Atypical acitivties of the Prefrontal cortex, Hippocampus and Amygdala

Tourettes Disorder

Disorder of tics (involuntary repetitive stereotyped movements or vocalizations)

-Motor Tics involve movements, whereas Verbal tics involve vocalization

Common motor tics include hitting, touching objects, squatting, twirling and lewd gestures

Common verbal tics include inarticulate sounds (barking, coughing, grunting, repeating words) and uttering curses

-Symptoms gradually subside as the patient matures

Neural Basis of Tourettes Disorder

-Involves a smaller volume of the Striatum

-Suppression of tics results in activity in the prefrontal cortex and the caudate, indicating dysfunctional caudate unable to suppress unwanted movements

-Dysfunctional dopaminergic and GABAergic signaling in brain circuits involved in habit-formation (cortex, striatum and the thalamus)

-Thinning of the gray matter of the sensory motor cortex that controls the face, mouth and voice-box