Whoever fights monsters...

Capgras’ Syndrome

This delusional misidentification phenomenon causes the afflicted individual to believe others to be, or experiences others as, imposters who have impersonated or replaced familiar individuals. Capgras’ Syndrome is common in patients with Alzheimer’s. 

Example: An older man, finding his wife sitting in their kitchen, orders her out of his house, accuses her of pretending to be his wife, and demands to be taken to his real wife immediately.

Synaesthesia: 

a neurologically-based condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway.

The sensory links are intermixed. When a person senses something, automatically, another sensation lights up. For example patients see letters in different colors, some might see music, or taste words, days of the week have personalities, and some experience to see time, etc The picture depicts a synesthete being able to taste color.

Alien Hand Syndrome

A neurological disorder in which the person’s afflicted hand appears to take on a mind of its own. 

Alien hand syndrome is best documented in cases where a person has had the two hemispheres of their brain surgically separated, a procedure sometimes used to relieve the symptoms of extreme cases of epilepsy. It also occurs in some cases after other brain surgery, strokes, or infections.

The locus coeruleus (LC)  (also spelled locus caeruleus or locus ceruleus), is a nucleus in the brainstem involved with physiological responses to stress and panic.

As an important homeostatic control center of the body, the locus coeruleus receives afferents from the hypothalamus. The cingulate gyrus and the amygdala also innervate the LC, allowing emotional pain and stressors to trigger noradrenergic responses.

The locus coeruleus is responsible for mediating many of the sympathetic effects during stress. The locus coeruleus is activated by stress, and will respond by increasing norepinephrine secretion, which in turn will alter cognitive function (through the prefrontal cortex), increase motivation (through nucleus accumbens), activate the hypothalamic-pituitary-adrenal axis, and increase the sympathetic discharge/inhibit parasympathetic tone (through the brainstem). Specific to the activation of the hypothalamo-pituitary adrenal axis, norepinephrine will stimulate the secretion of corticotropin-releasing factor from the hypothalamus, which induces adrenocorticotropic hormone release from the anterior pituitary and subsequent cortisol synthesis in the adrenal glands. Norepinephrine released from locus coeruleus will feedback to inhibit its production, and corticotropin-releasing hormone will feedback to inhibit its production, while positively feeding to the locus coeruleus to increase norepinephrine production.

The LC’s role in cognitive function in relation to stress is complex and multi-modal. Norepinephrine released from the LC can act on α2 receptors to increase working memory, or an excess of NE may decrease working memory by binding to the lower affinity α1 receptors.

mindovermatterzine:

I realized that many of the things I want to write about on this blog mention, at least in passing, areas of the brain and how their functioning might influence our mental health. I set up Mind Over Matter in the hope of being able to provide a platform for patients, public & practitioners to engage in discussion of their experiences of mental health issues on a common level, but dropping neuroscience into this arena without explanation would put some of these groups at a disadvantage.  With that in mind, here follows a whistle-stop tour of the brain. I do not claim this to be an exhaustive explanation, merely a little introduction to the basics…

The pink area above is the cerebral cortex, which is split into lobes. The frontal lobe (at the front, surprisingly), is associated with the executive cognitive functions, such as planning and decision making, error correction, responses in novel situations and inhibition of prepotent responses. Some of these executive functions are thought to be impaired in several psychiatric disorders, such as schizophrenia, where these so-called ‘cognitive symptoms’ may sometimes be the first to emerge in the prodromal phase of the disorder (i.e. before specific, differentiating symptoms occur). 

The parietal lobe lies behind it and combines sensory information from different modalities.  Some people with borderline personality disorder describe multi-modal hallucinations and can show impaired visuospatial capacity, which suggests some kind of different processing here.  

The occipital lobe lies at the back of the brain and contains the visual cortex for processing of visual information from the optic nerve. I can’t think of anything off the top of my head about this lobe that would be relevant to psychiatry.  

Last but not least is the temporal lobe, which we can’t actually see on this diagram because it is a sagittal section of the brain (dividing it from front to back into left and right portions) but, as the name suggests, it lies at the temples of the head.  This area contains the auditory cortex and is thought to be associated with the auditory hallucinations common in schizophrenia.  Interestingly, epilepsy in this area often leads to religious or spiritual sensations.  It also contains the hippocampus and amygdala (see below).

The corpus callosum is a collection of about a quarter of a billion neuronal fibers connecting the left and right hemispheres.  It is sometimes surgically severed in patients with intractable epilepsy to stop the massive seizures spreading from one half of the brain to the other & thus to minimise the damage involved.  It was found that many of these patients showed an odd phenomenon after surgery of ‘split consciousness’. 

The ventricles form a system of four communicating cavities that are continuous with the central canal of the spinal cord.  It has been consistently shown that the lateral ventricles of schizophrenics are larger than controls, which relates to a lateral displacement of the corpus callosum in these individuals too.

Above we zoom in to view the hypothalamus, which controls body temperature, hunger, thirst, fatigue, sleep and the circadian cycles.  The lateral hypothalamus is associated with hunger: lesioning this area causes a decrease in food intake & stimulating it causes an increase.  The opposite pattern is found for the ventromedial hypothalamis, which is therefore identified as the ‘satiety centre’ of the brain.  Because of its association with food intake, the hypothalamus is of great interest to researchers looking at a possible cause of eating disorders.  It also forms part of the HPA axis (hypothalamic pituitary adrenal axis), which controls bodily responses to stress and is thought to be implicated in mood and anxiety disorders.

Above is the hippocampus.  It is actually so named because it looks like a seahorse (hippocampe in French) - allegedly, but I struggle to see it. It plays an important role in long term memory and spatial navigation, but crops up in the literature concerning many psychiatric disorders too.  It contains an area called the dentate gyrus, which is one of only a few areas in which adult neurogenesis (the birth of new neurons) occurs in humans.

Very near to this area is the amygdala, which is particularly involved in emotional learning and fear conditioning.  This structure seems to be particularly sensitive in the anxious.

That was all highly generalised, but it was fun to try to write off the top of my head. Obviously there are hundreds more structures in the brain but I hope that this was a passable introduction!