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Methamphetamine, also called meth or crystal meth, among other names, is a psychostimulant drug mainly known for its recreational use. Methamphetamine is chemically similar to amphetamine, a drug used to treat attention-deficit hyperactivity disorder, obesity and narcolepsy; but being more potent and highly addictive, methamphetamine is rarely prescribed for medical treatments. Most commonly, the drug is produced illegally, from pseudoephedrine, an ingredient in cold medicines. It can exist as white powder, pills, or bluish-white crystals, and can be consumed by swallowing, smoking, snorting, or injecting.
Methamphetamine acts to increase the amount of a neurotransmitter called dopamine in the brain. Dopamine is at the basis of the brain reward pathway, which is designed to “reward” the body for important behaviors that are essential for survival, such as feeding when hungry. Engaging in enjoyable activities causes dopamine release from dopamine-producing neurons into a space between neurons, where it binds to and stimulates its receptors on the neighboring neuron. This stimulation is believed to produce pleasurable feelings or rewarding effect.
Normally, dopamine molecules are promptly cleared from the synaptic space to ensure that the postsynaptic neurons are not over-stimulated. This is possible thanks to the action of dopamine-transporter, which channels dopamine back to the transmitting neuron.
Methamphetamine binds to dopamine-transporter and blocks dopamine re-uptake. In addition, it can enter the transmitting neuron and trigger more dopamine release. The result is that dopamine builds-up in the synapse to a much greater amount than normal. This produces a continuous over-stimulation of receiving neurons and is responsible for the prolonged and intense euphoria experienced by drug users.
At a low dose, methamphetamine stimulates the brain and can elevate mood and alertness; and by accelerating heart rate and breathing rate, it increases energy in fatigued individuals. It also reduces appetite and promotes weight loss. These seemingly “positive” effects keep users coming back for more, eventually leading to addiction and potential overdose. Long-term drug users may experience extreme weight loss, severe dental damage, and constant hyperactivity which results in anxiety, sleeping disorders and violent behaviors.
Overdose takes the drug’s effects to the extreme and can cause psychosis, heart attacks, seizures, strokes, organ failures, and even death.
Currently, there is no approved pharmacological treatment for methamphetamine addiction; the most effective treatments are cognitive behavioral therapies.

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Synesthesia is a phenomenon in which stimulation of a certain sensation leads to a simultaneous activation of another unrelated sensory pathway. For example, some synesthetes see colors when they hear sounds, while others can taste distinct flavors when they hear unrelated words. Remarkably, this involves not only the five senses, but also cognitive and mental experiences such as pattern recognition, spatial orientation or even emotions. Some forms of synesthesia involve more than two senses or experiences at a time.
In theory, there can be as many types of synesthesia as there are possible combinations of sensory or perceptual experiences, but some forms are much more common than others. These include: grapheme-to-color synesthesia, where individual letters and numbers are seen with a specific color; sound-to-color, or chromesthesia, where sounds produce colors; and spatial sequence synesthesia where elements of a sequence, such as days in a week, are assigned a specific location in a 3D arrangement around the person. It’s not uncommon for a person to experience more than one form.
Once thought to be rare, synesthesia is now estimated to be very common. The numbers are far from accurate, however, perhaps because most synesthetes have their experiences since a very young age and do not realize that anything is “unusual” until much later in life, at which point many tend to keep it a secret for fear of being different or diagnosed with mental illness. With today’s better understanding of the phenomenon, synesthetes are more likely to come forward sharing their experience. Despite being referred to as a neurological condition by some neurologists, synesthesia is not a disease; it is not associated with cognitive or mental disabilities. In fact synesthetes generally perform better in memory tests than an average person and tend to be more creative. They have built-in capabilities that are to their advantage: seeing colors when hearing musical notes can help achieve perfect pitch; automatically arranging items in space aids with memory; and having numbers color-coded can help quickly spot differences and patterns. Most synesthetes perceive their experiences as a gift rather than a handicap. Many tend to have inclination for creative, artistic professions.
A “true” synesthetic experience is automatic, involuntary and consistent over time. These experiences are the only way a synesthete perceives the world: a sound, or a letter, always gives the same color, every time without fail; and if they hear a new sound they never heard before, or see a new character they never seen before, a color will be automatically assigned to it.
Some drugs may produce synesthetic-like effects but these are not real synesthetic experience because they do not last.
Genetic make-up seems to have a role in predisposition to synesthesia as it tends to run in family, but family members can have different forms of synesthesia.
Mechanism of synesthesia is still poorly understood, but there is evidence that the cross-talk between various sensory pathways accounts for the experience. For example, with the help of brain imaging techniques, the brain V4 region responsible for color recognition can be seen activated when a sound-to-color synesthete is presented with auditory stimuli. Synesthetes also seem to have more grey matter in the implicated brain areas, as well as more white matter connecting them.
There is a theory that we are all born synesthetic, with all the connections between senses, but lose them, together with synesthetic ability, as our brain matures, while synesthetes retain it. This may explains why most people still have some degree of synesthesia as adults.

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Synaptic pruning is the process of synapse removal that takes place naturally, as part of brain maturation. A human brain starts its development in early embryonic stage and reaches the maximum number of synaptic connections sometime in early childhood, at which point it is about double of what is normally present in an adult brain. This is when the elimination of excess neuronal synapses, known as synaptic pruning, begins. The process removes roughly half of all synapses, and occurs mainly during adolescence, but may continue well into young adulthood. By getting rid of unnecessary connections, synaptic pruning helps to refine neural circuits and increase network efficiency.

Computational models suggest that learning performance is optimal when synaptic connections are first over-generated and then pruned. An analogy is the task of writing an essay: the easiest way is to put all possible ideas into a longer-than-needed first draft, then trim it to keep only the essential points to create an effective final message.

Synaptic pruning is activity-driven, and follows the “use it or lose it” rule – synapses that are rarely used are eliminated, while frequently used synapses are protected from removal.  In fact, it has been shown that activation of the glutamate receptor NMDA, a marker associated with long-term memory retention and learning, is the major protective factor for a synapse. Thus, active synapses are selectively stabilized, while superfluous synapses are eliminated.

While the mechanism underlying synaptic pruning is, in most part, still a mystery, recent studies have implicated the brain’s supportive cells, known as glial cells, or glia. Specifically, two types of glia – astrocytes and microglia – are responsible for identifying and removing unnecessary neural connections. A number of signaling molecules are involved in control of glial cell movement, target recognition and ingestion.

Given the important role of synaptic pruning in sculpturing and refining the brain’s neural circuits, it is plausible that aberrant synaptic pruning is associated with a number of neurological disorders such as schizophrenia, autism and epilepsy. Too much pruning results in shortage of connections and is thought to underlie schizophrenia. The first occurrence of schizophrenia symptoms, typically in late adolescence or early adulthood, coincides with the time when synaptic pruning is most prominent.

Too little pruning, on the other hand, leaves the brain with too many redundant connections, which can be confusing, inefficient and may limit learning potential. Excessive synapses are observed in autism spectrum disorders, and epilepsy.