Thursday, September 27, 2007

Language In Our Life And Its Role In Our Brain

The early studies done in this area were by Broca (1861) and Wernicke
(1874). Broca's work included the patient, now known as "tan", who
could only say the word "tan", although his speech comprehension
stayed in tact. The patient died shortly afterwards and autopsy
revealed that he had been damaged in the lower part of the left
frontal lobe. Broca collected eight more cases and concluded that the
identified area was essential in the production and comprehension of
speech. The area is called Broca's area and the condition of damage to
it is called Broca's aphasia.

Wernicke reported a different aphasia. Patients could speak in
organized and grammatical sentences, although what they said seemed to
have little to do with the on going conversation. On the other hand
they seemed to have no understanding of what was spoken to them. On
autopsy, they all had damage to an area at the top of the left
temporal lobe, now known as Wernicke's area.

These speech zones also tally with the sensory and motor cortical
mechanisms. For example, Wernicke's aphasia represents a problem with
speech processing. The spoken word is a sound stimulus which enters
our ear and in transferred as an electrical signal through our nerves
until it reaches the primary auditory cortex in the temporal lobe.
This area is close to Wernicke's area which contains the "word
analyzer". The word analyzer contains the sound patterns of words
that are essential in converting speech into words. If Wernicke's are
damaged the sounds cannot be identified as speech and comprehended.

We humans have a wonderful opportunity to communicate with each other both spoken and written languages, unlike our "smaller brothers" from animal world who can only use some specific signals which are recognized by them only. Language is a very powerful tool that enables us not only to communicate, but also plays a vital part in our brain's development and simply "working'.

Broca's area is in the frontal lobe and contains the motor cortex.
Speech is a motor process requiring sophisticated control over muscles
of the throat, lips and mouth. Broca's area contains the motor plans
for words. When Broca's damaged the plans cannot be activated
even though the motor cortex is intact.

Speech, reading and writing are also language functions that have a
role in the human brain. Aphasia study showed that the condition was
more common in left hemisphere damage than in right. In contrast to
the symmetry of sensory and motor functions, language functions are
asymmetrical, being more dominant in the left hemisphere. Global
aphasia is when both Broca's and Wernicke's areas are damaged and
"shadowing" experiments in which words are spoken to a subject quickly
and they must repeat them back quickly suggest that a global aphasic
will be unable to "shadow". The accurate fasciculus's the direct
pathway from Wernicke's to Broca's area. If this is damaged then
conduction aphasia results, which is severe impairment of repetition or
"shadowing". However, normal speech production and comprehension are
less affected. This implies other less direct pathways exist apart
from the direct pathway of accurate fascicules.

Writing, as a motor process is produced from the motor cortex under
the control of the planning centre in Broca's area. The input system,
reading, involves the visual system and a region that contains the
visual pattern of words and is capable of converting visual input into
words. The key region for reading and writing is the angular gyros, on
the borders of the temporal and parietal lobes.

This region contains visual word patterns, the visual pattern is
transmitted to Wernicke's area, where it arouses the auditory form of
the word and comprehension occurs. Pure word blindness occurs when we
have someone able to write a page of coherent and fluent prose, but
who cannot read it back. This syndrome is known as alexia without