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Tuesday, May 21, 2019

Serotonin

Serotonin


Serotonin (5-hydroxytryptamine) is a neurotransmitter that is primarily involved in mood regulation. The neuromodulator is best known for its involvement in depression, although its malfunction has also been implicated in other psychiatric conditions, such as Generalized Anxiety Disorder, Obsessive-Compulsive Disorder, Attention-Deficit Hyperactivity Disorder, Borderline Personality Disorder, Post-Partum Blues, Autism, eating disorders, panic attacks, phobias and even Schizophrenia (an affliction also involving dopamine overabundance).

Patients with Major Depressive Disorder produce less serotonin as measured by neuroimaging techniques, and this finding is the basis for the common medications used to treat depression, selective serotonin reuptake inhibitors (SSRI). Perhaps the most famous SSRI is fluoxetine, brand name Prozac. The production of serotonin may depend on whether the individual is homozygous (two copies) or heterozygous (one copy) of the 5-HT short allele, homozygotes are more likely to succumb to depression even if under the same stressful circumstances than heterozygotes or those who have not inherited that allele at all (Caspi et al., 2003). Individuals with two copies of the long 5-HT allele are the least prone to developing the illness. Notwithstanding, in their meta-analysis across studies, Risch et al. (2009) found little evidence supporting this result.

According to Nugent et al. (2008), severe tryptophan depletion leads to a relapse of depressive symptoms. Tryptophan is an essential amino acid found in aliments such as pasta and turkey and a precursor to serotonin synthesis. In the experiment, subjects returned to normal as soon as tryptophan was reincorporated into their diet.

In their review of findings, Russo et al. (2009) cite several authors that have attested to serotonin mediating sleep, aggression, anxiety, thermoregulation, satiety and stress, Curiously, neurogenesis also seems to depend on serotonin. The reviewers also explain the brain reaction to low tryptophan blood plasma levels and “speculate about the possible survival value of this mechanism” (259).

Neurogenesis is the appearance of new brain cells (neurons) and Banasr et al. (2004) found that adult neurogenesis is enhanced by serotonin agonists (agonists stimulate, antagonists inhibit). Several receptor subtypes are implicated in the process, and the scientists came to the conclusion that serotonin was beneficial to adult cell proliferation, especially in the following brain regions: subgranular layer (SGL), subventricular zone (SVZ), dentate gyrus (DG) and olfactory bulb. A small reminder that gyrus (plural form gyri) refers to convex parts of the brain surface gray matter, while sulci (singular form sulcus) denote concave parts.

Dayan et al. (2008) suggest that serotonin deficiency mitigates impulse control by lowering inhibition, thus making the action with potentially adverse consequences more likely. The authors also discuss serotonergic pathways’ implication in thought processes related to aversive thought processes. Recalling that in encountering a new stimulus, an organism is often faced with an internal aversion versus approach conflict, the decision resting on whether the object in question poses a threat or promises a reward, respectively.

“Most people are about as happy as their self confidence will allow them to be.” (Shannon L. Alder). Illustration : Megan Jorgensen.

References:

  • Banasr, M., Hery, M., Printemps, R. & Daszuta, A. (2004). Neuropsychopharmacology, 29 (3): 450-60.
  • Caspi, A., Sugden, K., Moffitt, T. E., Taylor, A., Craig, I. W., Harrington, HL., McClay, J., Mill, J., Martin, J., Braithwaite, A. & Poulton, R. (2003). Influence of life stress on depression: Moderation by a polymorphism in the 5-HTT gene. Science, 301 (5631): 386-9.
  • Dayan, P.  & Huys, Q. J. M. (2008). Serotonin, inhibition and negative mood. PLoS Computational Biology, 4 (2): 0001-11.
  • Nugent, A. C, Neumeister, A., Goldman, D., Herscovitch, P., Charney, D. S. & Drevets, W. C. (2008). Serotonin transporter genotype and depressive phenotype determination by discriminant analysis of glucose metabolism under acute tryptophan depletion. Neuroimage, 43(4): 764–774
  • Risch, N., Herrell, R., Lehner, T., Liang, K. -Y., Eaves, L., Hoh, J., Griem, A., Kovacs, M., Ott, J. & Merikangas, K. R. (2009). Interaction between the serotonin transporter gene (5-HTTLPR), stressful life events and risk of depression: A meta-analysis. JAMA, 301(23): 2462–2471.
  • Russo, S., Kema, I. P., Bosker, F., Haavik, J. & Korf, J. (2009). Tryptophan as an evolutionary conserved signal to brain serotonin: Molecular evidence and psychiatric implications. The World Journal of Biological Psychiatry, 10: 258-68.

Murder in the Paradise

The Life and Death of Stars


Most processes occurring in the visible universe involve stars in some way. In fact, all elements, with just a few exceptions, were formed in the nuclear furnaces of stars. This includes the heavier elements such as oxygen and carbon, the main constituents of living organisms (among the exceptions we find lithium, deuterium, helium, hydrogen which were created in the big bang).

Astronomers classify stars using many schemas, including their color, brightness, size, temperature, mass, association with other stars. The system of magnitude of stars introduced by the Greek astronomer Hipparchus in the second century AD is still in use today. Hipparchus divided stars by visual brightness from magnitude 1 (brightest) to magnitude 6 (faintest). Each level represents a 2.5-fold change in brightness.

With the arrival of the telescope and later the camera, stars as faint as magnitude 30 became detectable. These stars are four billion times fainter than could be observed with the naked eye.

The modern and most meaningful way of characterizing and analyzing stars is by spectral class. We classify them by the letters OBAFGKM (the famous mnemonic for remembering this sequence is Oh, Be A Fine Girl, Kiss Me). A star’s spectral class is defined by its characteristics of temperature, size, and density. The hottest and most massive stars are in the O and B classes and typically emit blue to white light. Stars of intermediate temperature and mass range from A- to G-type and emit white to yellow light. The coolest, least massive stars are K- and M-type and emit orange to red light. In fact, two new classes have been added (L and T) to account for the discovery of very low-mass stars.

The lifetime of a star is directly related to its mass. Indeed, stars that are actively fusing hydrogen to helium, such as our Sun, are called main-sequence stars. We know that stars generally spend about 90 percent of their lives on the main sequence. And when stars exhaust their hydrogen fuel, they begin the inevitable process of stellar death.

At the point of “stellar death” in their evolution, stars begin to leave the main sequence.

Thus the most massive stars rapidly use up their fuel and may live only a few million years. This is in contrast to lower-mass stars, such as the Sun, which may enjoy a main-sequence life of over ten billion years.

As a sun-like star exhausts its hydrogen core and begins to die, a new process begins. Helium fuses to carbon and later to oxygen, which will sustain the star for a short period but at the expense of further core collapse, higher core temperatures, and continued surface expansion. The surface of the star, no longer checked by gravity, bloats and cools. At this stage, the star is referred as a red giant and the bloated diameter can exceed ten times that of our Sun. The star begins a futile cycle of further core collapse and surface expansion that can end either passively as a white dwarf surrounded by a planetary nebula or, for more massive stars, in a cataclysmic explosion known as a supernova.

Steller death is an inevitable stage in the evolution of every star. Image by © Megan Jorgensen.

Lost

Lost

By Gregory Maguire


Waugh was an overweight estate agent with a belt made of rattlesnake skin. He huffed and panted as he led Winnie toward the back of the flat where a man and a woman where muttering to themselves in disagreement. “My clients are nearly through here but we have another place to see down on Honeybourn Road,” said Kendall Waugh. “Let me just answer their questions, Miss Prizzy, and then I'll show you round quickly.”

“I can have a look myself,” she said. She was looking as she spoke. The layout of the flat for sale was identical to John's flat above, and, she assumed, to Mrs Maddingly's flat below. These small rooms in the older building, facing Weatherhall Walk, two additional rooms snugly joined to her newer house behind. The flat had belonged to Mrs. Maddingly several decades ago, but there was no sign of her whimsical disarray. The place was empty of furniture and sorely need of sprucing up. The coping was dingy. But Winnie wasn't in the market for a flat, she was supposed to be hunting for some natural cause of the unnatural disasters occurring in John's flat upstairs.

She could see nothing of interest. The chimney stack rose from below and continued above, exactly as geometry and architecture would have it. In the large room it had once heated and lit, the chimney breast was boarded over. “Could this fireplace be opened up and made to work?” she said to Kendall Waugh.

“I'll just finish here if I may have a moment, one moment,” he called, affecting patience, but unconvincingly. Winnie stood in the gloom, in a box of cold room, and heard the voices in the annex. In certain sorts of rain, when the clouds came down close as they were today, it was sometimes hard to keep the mind fixed to the current year.

She's noticed the syndrome mostly on gray February days, back when she was living in the more expensive and so more thinly developed Boston suburbs. The wet tree trunks, the low sky the color of tarnished silver, the muted smoky green of of yews and white pines and arborvitae, the retracting mounds of dirty snow, the skin of the world pulling in phlegmy puddles, the occasional stab of red in holly berries, it was the same cold world of the Wampanoags, the Puritans, the colonists and revolutionaries, the Federalists, and revivalists, and Victorians, and so on.

Similarly, in London, the wind bullied the windows in their casing as rattingly as it must have done all through the past three hundred years and more. The gray skies drawn in over the mighty and inattentive Atlantic were the very same gray, corrected for reduction of pollution from coal fires, of course, thanks to the Clean Air Act.

She roused herself back to whatever of the here and now she could still trust, or care about. She heard Kenndall Waugh answering a question. ”That, I can tell you actually. We've got at the office a very fine pamphlet that talks about this street and actually mentions the structure. It was put up in the early nineteenth century, which makes it almost two hundred years old of course as you know, by a merchant named Rudge. Rudge House and all that. He was in imports, the tea trade.”

Lost. Photo by Elena.

Dopamine

Dopamine


Dopamine is one of the major excitatory neurotransmitters in the brain. The neurochemical of the catecholamine group has been associated with reward mechanisms, novelty seeking, addiction and other behavioral and biological phenomena.

Too much dopamine has been linked to schizophrenia, too little to Parkinson’s disease (which is why patients taking antipsychotics would usually not be prescribed dopamine agonists, while patients with Parkinson’s disease are given L-Dopa, a dopamine precursor).

The present paper will attempt to highlight some of the repercussions dopamine has on the human experience. The involvement of dopamine in reward anticipation has largely been established. Ikemoto (2007) reviews scientific literature to arrive at a better understanding of the dopamine reward circuitry. For example, laboratory rats and mice learn to self-administer drugs of abuse unless they were given dopamine blockers (for a list of works see Ikemoto, 2007).

There are several types of dopamine receptors (D1, D2, D3, D4 and D5), persons with pathological overeating features have been found to have abnormally low quantities of D2 type receptors. Wang et al., (2001) used PET (positron emission tomography) scans to measure D2 receptors distribution in obese subjects compared to controls.

Too much dopamine has been linked to schizophrenia, too little to Parkinson’s disease. Photo by Elena.

The number of receptors correlated negatively with BMI (i.e. as recorded BMI increased, listed D2 numbers decreased; body mass index, underweight below 18.5, obese above 30). The authors hypothesized that since dopamine is responsible for motivation and reward feelings, individuals lacking dopamine may be overindulging to fill the chemical messenger void. Thus, by enhancing dopamine activity in persons with the condition, it may be possible to stop overeating in such cases.

Conversely, the opposite is true in patients with schizophrenia, they have an abnormally high D2 activity, which is predicted by the classic hypothesis that schizophrenia is related to dopamine hyperactivity leading to the logical consequence that all antipsychotics act as dopamine antagonists. Interestingly, in their article, Seeman & Kapur (2000) expose the contradiction that surrounds D2 receptors and the mental illness.

Some previous studies in vivo have found abnormalities, some failed to do so. Further, the authors caution that since most studies that have found increased D2 population in the striata of patients with schizophrenia postmortem were done following antipsychotic use, the drugs may have influenced the outcomes. In reviewing a vast array of literature, Huey et al. (2006) came to the conclusion that patients with frontotemporal dementia (FTD) exhibited a dopaminergic deficiency.

Other neurotransmitter circuits they covered in their meta-analysis were serotonin, also deficient, and acetylcholine, appearing undamaged in FTD. However, they warn that the studies surveyed were challenged in sample size and lacked control groups, a potential limitation of the comparison. Loss of dopamine producing neurons is a distinctive feature of Parkinson’s disease (Lotharius & Brundin, 2002). As expected, the personality trait of novelty seeking, prompted by dopamine, is diminished in patients with the illness (Menza et al., 1993). Still it is unclear whether such conservatism is due to dopamine deficiency or reclusiveness brought on by the confines caused by the disease.

Benjamin et al. (1996) found that having two copies of the long allele of the D4DR gene led to higher scores on the NEO-PI-R personality questionnaire in areas coding for novelty seeking, and its components: exploratory excitability, extravagance and disorderliness. The conscientiousness (lower) and extraversion (higher) dimension were also correlated with the genotype. However, the experimenters remark that the polymorphism accounts for only part of the story since other genes are similarly involved in producing the phenotypes.

The five types of dopamine receptors are D1, D2, D3, D4 and D5. The neurotransmitter is associated interalia, with reward. Image: Elena.

References:


  • Benjamin, J., Li, L., Patterson, C., Greenberg, B.D., Murphy, D.L. & Hamer, D.H. (1996). Population and familial association between the D4 dopamine receptor gene and measures of Novelty Seeking. Nature Genetics, 12  (January): 81-4.
  • Huey, E.D., Putnam, K.T. & Grafman, J. (2006). A systematic review of neurotransmitter deficits and treatments in frontotemporal dementia. Neurology, 66 (1): 17-22.
  • Ikemoto, S. (2007). Dopamine reward circuitry: Two projection systems form the ventral midbrain to the nucleus accumbens-olfactory tubercle complex. Brain Research Reviews, 56 (1): 27-78.
  • Lotharuis, J. & Brundin, P. (2002). Pathogenesis of Parkinson’s disease: Dopamine, Vesicles and -synuclein. Nature Reviews Neuroscience, 3 (12): 932-42.
  • Menza, M.A., Golbe, L.I., Cody, R.A. & Forman, N.E. (1993). Dopamine-related personality traits in Parkinson’s disease. Neurology, 43 (3): 505-508.
  • Seeman, P. & Kapur, S. (2000). Schizophrenia: More dopamine, more D2 receptors. Proceedings of the National Academy of Sciences of the United States of America, 97 (14): 7673-75.
  • Wang, G. -J., Volkow, N.D., Logan, J., Pappas, N.R., Wong, C.T., Zhu, W., Netusil, N. & Fowler, J.S. (2001). Brain dopamine and obesity. The Lancet, 357 (9253): 354-57.

Monday, May 20, 2019

Computational Psychology

Computational Psychology


Psychology is everywhere. Body language analysis is one such example. You know… that if a person’s feet are pointed away from you, then they do not like you or that if their arms are closed, any potential deal if off. Psychology graduates often end up in business jobs and careers, no surprise there, given the overlapping fields of organizational behaviour, industrial relations and occupational psychology.

Computational neuroscience studies the information systems of the brain, the neural transduction of electrical current into meaningful concepts. Psychology is like the Borg (Star trek cybernetic race). Psychology assimilates and resistance is futile. The field may be roughly pictured as psychology assimilating engineering and computer science. Well, we’re sure you get the idea.

Developmental psychology, also called child psychology, follows the individual throughout the lifespan. Computational modelling is of great service to the discipline (Mareschal & Thomas, 2007). An advantage of the approach is that it eliminates mandatory reliance on subjective views.

The science itself debuted in the 70s and 80s, while the appearance of the connectionist model explaining cognitive, perceptive and linguistic phenomena quickly followed. The authors testify that intelligent computers are indeed upon us. In effect, the first intelligent computer was Logic Theorist, the first one such machine able to process symbols. Olsson (2008) reasserts that no existing model can not only compute but also explain all learning.

Computational psychology. Illustration by Elena.

Computational psychology and neuroscience have greatly contributed to the elucidation of nature’s mysteries. Computational psychology is closely related to linguistics. One of the best-known figures in linguistics is Noam Chomsky; some of his material is also used in the psychological fields of memory, learning and behaviour. The overlap occurs naturally since psychologists are interested in the acquisition, use and preservation of language.

Mysterians believe that despite all the computations that can be modelled, the true essence of the mind will remain infinitely elusive. The mind modularity theorem and computationalism, paint a picture where files are stored and retrieved. Connectionism stems from the mental schema of conceptualizing brain processing as a computer web.

But how exactly does the cognitive science study the mind computationally? Sun (2008) provides the answer:

Research in computational cognitive modeling, or simply computational psychology, explores the essence of cognition (broadly defined, including motivation, emotion, perception, and so on) and various cognitive functionalities through developing detailed, process-based understanding by specifying corresponding computational models (in a broad sense) of representations, mechanisms, and processes.

Computational psychology greatly overlaps, even in its very definition, with cognitive science. Cognitive science in turn, relies on artificial intelligence and psychology among others to achieve its scientific goals. Ideally, future technological advances will permit to the related discipline to progress in its own way.

References:


  • Mareschal, D. & Thomas, M. S. C. (2007). Computational modelling in developmental psychology. IEEE Transactions of Evolutionary Computation, 11 (2): 1-14.
  • Olsson, S. (2008). Computational models of skill acquisition. In Sun, R. Ed., The Cambridge handbook of computational psychology. Cambridge University Press: Cambridge, UK.
  • Sun, R. (2008). Introduction to computational cognitive modelling. In Sun, R. Ed., The Cambridge handbook of computational psychology. Cambridge University Press: Cambridge, UK.

“Enlightenment is not imagining figures of light but making the darkness conscious.” Carl Gustav Jung, Swiss psychiatrist, psychologist, Founder of the Analytic Psychology (1875-1961). Photo : © Megan Jorgensen.