Dinishak.com MindBlog

All things between psychology and technology

April 29th, 2012

Most humans have a clearly dominant hand (usually the right one). What is the lowest form of life that shows such a preference or dominance? Why are most people right-handed?

Birds, which have neuronal populations in the left hemisphere that regulate their song production, are the lowest phylum with a convincing laterality or dominance. The reason for dominance—-its evolutionary or survival advantage—-is unknown.

There are many theories to account for the existence of dominance, but none of them really makes much sense.

March 12th, 2011

It is usually considered that the sense of smell is poorly developed in humans, in comparison, for example, to lower vertebrates, such as rats and mice. However, in view of its evolutionary significance, it seems very unlikely that the sense of smell is trivial in guiding human behavior.

The fragility of the fibers in the olfactory mucosa of the nose, their delicate passage through the cribriform plate, and the course of the olfactory tract along the orbital surface of the brain underly the vulnerability of this sensory modality to external trauma—for example, from head injury. This is compounded by the locations of structures receiving the central representations of smell, such as, for example, the primary olfactory cortex and olfactory tubercle, which lie vulnerable on the undersurface of the brain overlying the anterior perforated space.

Smell sensations may occur as part of an aura in temporal lobe epilepsy. Traditionally referred to as uncinate seizures (simple partial seizures in today’s terminology), the seizure focus was thought to be in the uncus, overlying the amygdala. However, olfactory inputs also end in the anterior insula, which thus may be associated with the experience. These aurae therefore have some localizing value, but they are not of lateralizing significance.

The olfactory system is involved in several neuropsychiatric disorders. In depression, for example, the sense of smell can be diminished, as may be other sensory modalities, such as taste or touch. Diminished smell sensation also has been reported in Alzheimer’s disease and Parkinson’s disease, especially the Lewy body variant but not sufficiently reliably to be used in any diagnostic way (Hawkes, 2003). Diminished smell also may be observed early in the course of schizophrenia and may be associated with smaller perirhinal cortices as measured with MRI (Turetsky et al., 2003). Thus, disturbances of smell in such disorders may be associated with underlying neuroanatomical deficits, rather than being simply a manifestation of a psychosis or deteriorating intellect.

September 6th, 2010

One of the unsolved puzzles of the brain is the question which code is being used when nerve cells communicate with each other. It has been known for more than a century that the basic unit of communication within the nervous system is the pulse-like fluctuation in voltage at the membrane of neurons. But there is still a hot ongoing debate on how these so-called action potentials are combined to form a code for the actual processing and transmission of information. Two forms of coding are popular candidates: one is based on the rate of action potentials (rate coding) and the other relies on the timing of their occurrences (temporal coding).
Researchers now propose that under certain conditions, both forms of coding can in fact be employed simultaneously.
Here is the full article spiking activity propagation in neuronal networks

August 14th, 2010

Really nice newsletter in pdf format from the Harvard Mahoney Neuroscience Institute; site has back issues from 1992.