Posts Tagged ‘thalamus’

UNTHINKABLE

January 4, 2019

The title of this post is identical to the title of a book by Helen Thomson. The subtitle is “An Extraordinary Journey Through the World’s Strangest Brains.” In the opening chapter Ms. Thomson provides an overview of the brain. The most recognizable region of the human brain is the cerebral cortex. It forms the outside shell and is divided into two almost identical hemispheres. Each side of the cortex is divided into four lobes, which together are responsible for all our most impressive mental functions. If you touch your forehead, the lobe closest to your finger is called the frontal cortex and it allows us to make decisions, controls our emotions and helps us understand the actions of others. It gives us all sorts of aspects of our personality; our ambition, our foresight and our moral standards.

If you were to trace your finger around either side of your head toward your ear, you would find the temporal lobe, which helps us understand the meaning of words and speech and gives us the ability to recognize people’s faces.

Run you finger up toward the crown of your ear and you’ll reach the parietal lobe, which is involved in many of our senses, as well as certain aspects of language.

Low down toward the nape of the neck is the occipital lobe, whose primary concern is vision.

Hanging of the back of the brain we have a second “little brain,” a distinctive cauliflower-shaped mass. This is the cerebellum and it is vital for our balance, movement and posture. The vast majority of the cerebellum connects to regions of the cortex that are involved in cognition, perception, language and emotional processing.
A review of maps of the cerebellum built from functional MRI brain scans confirmed that all major cortical regions have loops of connections running to and from the cerebellum. The cerebellum has conversations with different areas of the cortex: taking information from them, transforming it and sending it back to where it came from. One of the more unexpected connections was with the prefrontal cortex, which lies far from the cerebellum at the front of the brain and has long been considered the most advanced part of the brain. This region is in charge of abilities such as planning, impulse control, and emotional intelligence. It is disproportionately large and complex in humans compared with our closest species. To learn more about the cerebellum see the healthy memory blog post “The Brain’s Secret Powerhouse That Makes Us Who We Are.”

If you were to pry open the two hemispheres, you would find the brain stem, the area that controls each breath and every heartbeat, as well as the thalamus, which acts as a grand central station, relaying information back and forth between all the other regions.
The brain is full of cells called neurons which are too small to be see with the naked eye. These cells pass messages from one side of the brain to the other in the form of electrical impulses. Neurons branch out forming connections with its neighbors. If you were to count one of these connections every second, it would take you three million years to finish.

Ms. Thomson writes, “We now know the mind arises from the precise physical state of these neurons at any one moment. It is from this chaotic activity that our emotions appear, our personalities are formed. and our imaginations are stirred. It is arguably one of the most impressive and complex phenomena known to man.

So it’s not surprising that sometimes it al goes wrong.”

The Seat of all Passions

March 9, 2018

The title of this post is the title of a section in Daniel Goleman’s book “Emotional Intelligence.” In humans the amygdala (from the Greek word for “almond’) is an almond -shaped cluster of interconnected clusters perched above the brainstem, near the bottom of the limbic ring. There are two amygdalae, one on each side of the brain nested toward the side of the head. Our amygdalae are relatively large compared to that of any of our closest evolutionary cousins, the primates.

The amygdalae and the hippocampi (there is also a hippocampus on each side of our brains) were the two key parts of the primitive “nose brain” that gave rise to the cortex and the neocortex. These limbic structures do much or most of the brain’s learning and remembering; the amygdalae is the specialist for emotional matters. If the amygdalae is severed from the rest of the brain, the result is a striking inability to gauge the emotional significance of events; this condition is sometimes called “affective blindness.”

Here please indulge a digression by HM to one of the projects he did as a graduate student. It involved conducting surgeries and implanting electrodes into the amygdalae of rats. These rats were deprived of water for 24 hours and then given an opportunity to drink. An electric current was applied to the amygdalae of some rats when they drank the water. The control rats were not shocked. The following day, the rats that had been shocked refused to drink, whereas the control rats, of course, drank. If you find this study troublesome, so does HM. But it did provide definitive evidence regarding the role of the amygdalae.

A fellow human had his amygdalae surgically removed to control severe seizures. He became completely uninterested in people, preferring to sit in isolation with no human contact. Although perfectly capable of conversation, he no longer recognized close friends, relatives, or even his mother, and remained impassive in the face of their anguish at his indifference. Absent the amygdalae, all recognition of feeling as well as any feeling about feelings is lost. Life without the amygdalae is life stripped of personal meanings.

All passion depends on the amygdalae. Animals that have their amygdalae removed or severed lack fear and rage, lose the urge to compete or cooperate, and no longer have any sense of their place in their kind’s social order; emotion is blunted or absent. As the amygdalae were not destroyed in HM’s rats, the stimulated rats returned to normal.

Tears, an emotional signal unique to humans, are triggered by the amygdala and a nearby structure, the cingulate gyrus. Being held, stroked, or otherwise comforted soothes these same brain regions, and stops the sobbing. Absent amygdalae, there are no tears of sorrow to soothe.

Goleman writes, “the workings of the amygdala and its interplay with the neocortex are at the heart of emotional intelligence. When impulsive feeling overrides the rational—the newly discovered role for the amygdala is pivotal. Incoming signals from the senses let the amygdala scan every experience for trouble. This puts the amygdala in a powerful position in mental life, something like a psychological sentinel, challenging every situation, every perception, with but one question in mind, the most primitive: “Is this something I hate? That hurts me? Something I fear?” If so—if the moment at hand somehow draws a “Yes”—the amygdala reacts instantaneously, line a neural tripwire, telegraphing a message of crisis to all parts of the brain.”

“When it sounds an alarm, it sends urgent messages to every major part of the brain: it triggers the secretion of the body’s fight-or-flight hormones, mobilizes the centers for movement and activates the cardiovascular system, the muscles, and the gut. Other circuits from the amygdala signal the secretion of emergency dollops of the hormone norepinephrine to heighten the reactivity of key brain areas, including those that made the senses more alert, in effect setting the brain on edge. Additional signals from the amygdala tell the brainstem to fix the face in a fearful expression, freeze unrelated movements the muscles had underway, raise heart rate and blood pressure, slow breathing. Others rivet attention on the source of the fear, and prepare the muscles to react accordingly. Simultaneously, cortical memory systems are shuffled to retrieve any knowledge relevant to the emergency at hand, taking precedence over other strands of thought.”

The extensive web of neural connections of the amygdalae allows them, during an emotional emergency, to capture and drive much of the rest of the brain—including the rational mind.

Research by LeDoux showed that sensory signals from the eye or ear travel first in the brain to the thalamus, and then—across a single synapse—to the amygdala; a second signal from the thalamus is routed to the neocortex—the thinking brain. So the amygdala can respond before the neocortex, which mulls information though several levels of brain circuits before it fully perceives and finally initiates its more finely tailored response.

LeDoux concluded, “Anatomically the emotional system can act independently of the neocortex. Some emotional reactions and emotional memories can be formed without any conscious cognitive participation at all.” LeDoux conducted an experiment in which people acquired a preference for oddly shaped geometric figures that had been flashed at them so quickly that they had no conscious awareness of having seen them at all. Nevertheless, our cognitive unconscious will still have formed an opinion as to whether we like it or not, not just the identity of what we’ve seen. Goleman notes that “our emotions have a mind of their own, one which can hold view quite independently of our rational mind.”

© Douglas Griffith and healthymemory.wordpress.com, 2018. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

How Placebos Could Change Research and Practice

March 29, 2015

The title was on the cover of the April 2015 Monitor on Psychology of the American Psychological Association.  Inside the issue was an article by Stacy Lu, “Great expectations:  New research is leading to an understanding of how placebos work—findings that may lead to more effective treatments and better drug research.  Our understanding and attitudes towards placebos is advancing.

In one study neuroscience researcher Shaffer and his colleagues asked participants to apply a “powerful analgesic” on their hands and arms.  Then the researchers administered small bursts of heat where the cream had been applied.  The cream was actually petroleum jelly, but participants reported that the s-called powerful cream protected them from feeling as much of a burn  as a control cream.  Even after the researchers showed them that the active cream was just petroleum jelly, it made little difference.  The participants still reported less pain from the heat when they were re-tested versus the control cream (The Journal of Pain, 2015).

Today scientists are studying  placebos as a psychobiological  phenomenon and the placebo response as a potentially important part of the success of many medical treatments.  Psychological assessments, brain scans, and genotyping are used  to understand better how placebo responses work and to identify who may be most likely to respond to them.  Placebos are similar to cognitive therapies in that they tap into people’s beliefs that there’s hope and that they will get better.

A meta-analysis of 25 neuroimaging studies of pain and placebos conducted by Wager and Atlas of the National Center for Complementary and Integrative Health (NCCIH) found that people who took placebos and expected have reduced pain had less activity in brain regions associated with pain processing, including the dorsal anterior cingulate, thamalus, and insula (Handbook of Experimental Pharmacology, 2014).

Research suggests that placebos have the greater effect in neural systems involved with processing reward seeking, motivation, and emotion.  Placebos seem to work especially well in patients with depression, Parkinson’s disease, and pain.  All three conditions involve the neurotransmitter dopamine.  These are also areas where people can consciously monitor their own treatment results.

In a study of patients with Parkinson’s disease Wager and colleagues found that simply expecting medication altered brain activity in the striatum and ventromedial prefrontal cortex in brain areas associated with reward learning in ways similar to actual dopaminergic medication (Nature Neuroscience, 2014).

In another study of people with migraines, placebos elicited a response without any verbal cue to effectiveness,   Slavenka Kam-Hansen and colleagues openly labeled placebo pills for some patients who reported as much pain relief as those who also got a placebo but had been told that they’d received real medication. (Science Translational Medicine, 2014).

Genetics research has found that participants with a specific genotype related to having more dopamine in the prefrontal cortex reported having a larger effect from a placebo  treatment  than participants with a genotype that produces less dopamine in the prefrontal cortex (PLOS ONE, 2012).

Children seem to respond especially well to placebos.  In one study their placebo response was 5.6 that of adults (The Journal of Pain, 2014).

Patients are interested and enthusiastic about placebo  treatments.  They are pleased to discover that they can contribute to their own healing.

Ischemic Stroke and Cognitive Function

February 25, 2015

This blog post is largely based on an article by Marina Fernandez-Andujar and eleven others titled, “Remote Thalamic MIcrostructural  Abnormalities Related to Cognitive Function in Ischemic-Stroke Patients,” published in Neuropsychology (2014), 984-996. Ischemic Stroke or Transient Ischemic Attack (TIA) is a brief period of lack of blood flow to an area of the brain.  This impairs the function of brain cells, so a person suffering from TIA develops symptoms of brain function impairment, such as
Weakness of the face and/or arm, and/or leg muscles on one side of the body
Numbness of face and/or arm and/or leg on one side of the body
Inability to understand spoken language
Inability to speak
Unexplained dizziness or vertigo
Loss of vision through one eye
Double vision or blurry vision
These symptoms of a mini stroke/TIA disappear completely within 24 hours.  Nevertheless, it is important to visit an emergency room as soon as possible.  Even if the event occurred a few days ago, medical attention should still be sought.

The thalamus is a midline symmetrical structure of two halves, within the vertebrate brain, situated between the cerebral cortex and the midbrain. Some of its functions are the relaying of sensory and motor signals to the cerebral cortex, and the regulation of consciousness, sleep, and alertness. The two parts of the thalamus surround the third ventricle. It is the main product of the embryonic diencephalon.
The study compared 17 patients who had suffered right hemisphere ischemic stroke three months previously with 17 controls matched for age, sex, and years of education.

In the interest of brevity, technical terms will not be defined and certain details will be omitted. However, this article reports the results of sophisticated brain imaging and contains a wealth of information for the technical specialist.  Stroke patients showed lower fractional anisotropy (FA) values and higher mean diffusivity (MD) values in specific areas of the right thalamus compared with  controls.  In patients, decreased FA values were associated with lower verbal fluency performance in the right thalamus, and the left thalamus after adjusting for diabetes mellitus.  Increased MD values were associated with lower verbal fluency performance in the right hemisphere after adjusting for diabetes mellitus. The FA and MD values were not related to any cognitive function in the control participants.

Alzheimer’s research has been largely focused on neurofibrillary tangles and amyloid plaques in spite of autopsies indicating the presence of these abnormalities, but not cognitive or behavioral of Alzheimer’s symptoms during the lifetimes of these individuals.  It is important to be aware that dementia can also result from ischemic strokes or Type II diabetes mellitus.