The Half Decent Pharmaceutical Chemistry Blog

Language distinguishes humans from the other hominids (chimpanzees, gorillas, and orangutans). We can point out three major aspects of language: writing, reading and speaking, which is the easiest to explain, from a nonscientific point of view.

Interestingly, languages have some points in common in every culture: every person learns it at an early stage of life and every language presents its own syntax (subject, verb and complement: what varies is the order) and grammar (every language has rules).

Towards the end of the 19th century, Paul Broca and Carl Wernicke found the two, most important areas of human brain linked to the ability to speak.
Both studied a pathology generally called aphasia (inability to speak). It has to be pointed out that aphasia can mean either the inability to understand heard words or to speak. And that made a huge difference.
The two aphasias, in fact, depends on which of the two areas has been damaged: Wernicke's or Broca's area.

Both areas are in the left brain in right handed people. In 70% percent of left handed humans, they are on the same side, while the remaining 30% is divided into a 15% who has them on the right and a 15% in both hemispheres.

Wernicke's area is in the posterior temporal lobe and surrounds the primary auditory area. That is quite obvious, because of the links between listening and speaking.
Words reach A1 and, then, Wernicke's area, which contains sound images of heard words. Hence, thanks to this area, we can comprehend the words we hear.

The information is sent to the Broca's area by the arcuate fasciculus. Broca's area is situated in the left inferior frontal region and creates those programmes for moving the organs we use to articulate words (mouth, tongue, etc.).

It has to be said that there are other parts of our brain, which are involved in speaking: the supplementary language area and some zones of motor and somatosensory cortex.

For what concerns aphasias, according to the different functions of the damaged regions, we can explain the three different types: a damage of the Wernicke's area will result in a receptive aphasia (the patient can't understand any language) and one of the Broca's area in an expressive aphasia (the patient understand what heard but won't be able to repeat it or to reply).
A problem with the auxiliary areas causes a problem of speech arrest: the patient is likely to develop a variable inability to conclude phrases.

This is probably the first The-Half-Decent-Pharmaceutical-Chemistry-Blog-ish post. In fact, I put a nice artwork in order to smart up the whole thing.
You can say it's a double inspiration: Andy Warhol's Mao's portrait has been a frequent memory while studying how human brain analyzes colours.
So, this is my tribute to Andy Warhol: it's called Four Colours.

Atoms and molecules absorb light with a certain wavelength and the colour we perceive is its complementary. The object reflects or emits light with the remaining wavelengths.

Everybody knows we have two kinds of photoreceptors, namely cone and rod cells: cones are less common among the animals and fewer than rods in human retina.
Cones are concentrated in the part of the retina called fovea, which is the one we see with in daylight: we use to move it to focus our attention.
There are three different types of cones (Trichromatic Theory), generally referred as Blue, Green and Red. However, considering the sensitivity of their pigments, it is definitely more correct to name them S-, M- and L-cells (small, medium and long wavelength). Or, if you like colours, Blue, Bluish-Green and Yellowish-Green.

According to the wavelength of the light emitted by the object, the three cones are differently stimulated and their responses, in terms of frequency of action potential, vary.
Cone cells are connected to parvocellular ganglion cells only. The information, then, goes through magnocellular layers of the lateral geniculate nucleus and, reaches the primary visual cortex (V1).

Blobs are a group of cells of V1, located in the third layer. Blobs process colour information as cone cells, with the cells activated by specific wavelengths.
The information is sent to V2 rough stripes and, finally,the analysis of colour finishes in V4, where there are neurons which are sensitive to a small range of wavelength: this guarantees a very accurate analysis.
V4 cells are responsible for colour constancy too: looking at a complex scene (i.e. with varying lightning conditions), the colours of objects do not change.
In the end, the processed data are transmitted to the association temporal cortex.

Association areas are a distinctive characteristic of human brain. Many animals have motor and sensory cortex which are similar to ours.
What happens in these association regions of our brain is a complex interpretation of inner and outer information, which basically results in our own behaviour.

In particular, the temporal association cortex plays a key role in the identification and recognition of complicated stimuli.
This is not a surprise, considering that here is also located the so-called ventral stream, where our brain processes shape and colour of what the eyes see. In particular, the temporal lobe is the site of V3 and V4 areas.

As for most of the other regions of human brain, the function of the temporal association lobe has been understood with the help of patients who present specific issues in this part.
Prosopagnosis has been crucial, in this very case. This condition consists in the inability to recognize people, even very familiar to us, such as parents and relatives, and it's frequently a consequence of damages in the right inferior temporal lobe.

A milestone in the study of prosopagnosis is the article "CAN WE LOSE MEMORIES OF FACES - CONTENT SPECIFICITY AND AWARENESS IN A PROSOPAGNOSIC", ETCOFF NL; FREEMAN R; CAVE KR, JOURNAL OF COGNITIVE NEUROSCIENCE 3 (1): 25-41.
Here is described the case of patient, L.H., who developed prosopagnosis as a consequence of a severe head injury. He could recognize common objects, whether someone was a friend or not and, according to. voice, way of walking, posture, etc., he could even recognize someone's identity. However, when he had to use his visual memory only, he was at a loss.

Studies on monkeys have revealed that in the inferior temporal lobe there are groups of neurons whose frequency of action potentials is hugely increased when another monkey's face is shown.
These cells have the organization of those, simpler, present in the visual primary cortex (V1) for detecting the orientation of objects. Both types describes functional columns. It's easy to understand that, while the columns in V1 are innate, those which deal with faces develop according to our experiences (which, here, means life).
Each column, for example, have cells which are sensitive to the orientation of the face.

Interestingly, the studies with rhesus have shown that these cells won't increase their activity if we show the monkey an image containing parts of a real face and others, taken from, say, tools, in order to create a fake.

What is still unknown is how our brain actually recognize the different faces, but it's possible that different groups of neurons react varying their potential, according to the differences of shapes of our visage.

Boring Saturday night: staying home, watching the football match on TV (Italy v. Ukraine, I think) and trying to kill my headache.

Journalists are on strike here, so, the match is broadcasted without anyone telling exactly what you are seeing or giving you priceless information about players' nicknames.
This afternoon I studied how our auditory system works.
I find interesting the difference between sound wave and sound. Our brain detects the former, while sound should be defined as the perception of amplitude, frequency and  complexity of the wave.
To sum up, there is no sound without a centrel nervous system interpreting it. No music, no word, nothing.

Basically, the auditory system can be divided in three parts: ear, auditory nerve pathway and central auditory system.
Ear is composed by outer, middle and inner ear. Pinna and ear canal help sound waves to reach the inner parts. Then, these waves of pressure become liquid wave: the tympanum vibrates and, thanks to malleus, incus, and stapes, the stimulus is amplified.
Another membrane, called the oval window, allow the mechanical vibration to reach the cochlea, which is located in the labyrinth. Here is situated the organ of Corti: on top of it, there is a membrane, whose vibration moves hair cells.

These hair cells present mechanically gated ion channels: when they move, more potassium and calcium ions enter, resulting in a depolarization. This increases the quantity of neurotransmitters released, which react with the receptors on the membrane of primary sensory neurons (the ratio is 1:1).

Now, the mechanical stimulus has been converted into potential energy, which is carried by the vestibulocochlear nerve, until the left cochlear nucleus. Next step is the superior olive: from now on, the information goes to both brains (left and right, which has led to two theories that try to explain how we can understand where the sound came from).
Then, the message reaches the right inferior colliculus and, subsequently, medial geniculate nucleus.
The final step of this pathway is the temporal lobe, where, in the superior temporal gyrus, the primary auditory cortex is.

Frequency is determined by the position of the activated receptors: the closer to the oval window, the higher the frequency.
Amplitude by the amount of neurotransmitters. Complexity is analyzed by some of the cells of the primary auditory cortex, which have solely this task.

Oh, well, I've just realised, once again, I haven't talked about chemistry, but looking at the latest Nobel prize for chemistry...I'm probably on the right track for a successful career, eh?