Introduction
For several decades, scientists considered the brain as a major organ of the human body that is conditionally set to perform specific functions. Each brain region was then regarded to play a specific role in human behavior and that no other section of the brain could replace that function. However, research in neurology and psychology showed that the brain has the ability to reassign its regions to particular functions and abilities. This revolutionary observation of brain plasticity thus became a focus for further investigations. Sensory deprivation pertains to the intentional removal of a sensation of an individual in order to determine the association of a stimulus with a sensory experience. Conditions utilizing sensory deprivation serve as human experimental settings that provide researchers an opportunity investigate how the human brain responds to the absence of a specific sensory facility. Several conditions have been employed to test sensory capabilities among human subjects. These include the simple utilization of blindfolds which can impede an individual from seeing, or the use of earmuffs to prevent a person from hearing. The reactions of the study participants are studied and analyzed by researchers and conclusions are eventually presented. In addition, sensory deprivation conditions are also administered as a complementary treatment in the practice of alternative medicine.
Body
The developmental stages of the human body are similar to the rest of the vertebrate species, wherein the brain is one of the first organs that arise in a developing fetus. Based on evolutionary corollaries, the brain is a body organ that is expected to sense different stimuli in order to live and survive in the environment. The ability of a biological species to feel different kinds of sensations helps in adjusting to the current conditions of the environment. In the case of sensory deprivation, the loss of a particular sensation thus provides scientists to determine whether an organism is still capable of performing its normal functions and activities in the absence of at least one sensory function. Several reports have been published with regards to such conditions, in both humans and other mammalian species. One common observation that is often described in sensory deprivation researches is that the absence of one sensory function results in an improved capability of another sensory function.
In a recent research report authored by Nava et al. (2008), the function of the temporal region of the brain was investigated in hearing impaired individuals. This investigation was conducted by providing the study participants with an experimental setting wherein they needed to judge the succession of events through the use of visual actions. The experimental setup was designed that the visual observation could be performed at either the center or perimeter of their fields of view. In one setup, the visual stimuli were positioned at the exact opposite points of the field of view of the study participant and the actual stimulus that was delivered first should thus be identified. The visual targets were designed that these were delivered at different times yet the time difference was so close that it would be difficult to know which stimulus commenced first. At the same time, 12 healthy individuals with normal hearing capabilities were employed as controls. The investigation of Nava et al. (2008) showed that there were no significant differences between the test and control study groups in determining which one of two visual targets which were positioned in the center of their field of view was delivered first. However, the authors were very interested in their other result that the hearing impaired or deaf study participants showed a greater ability to discriminate visual targets that were positioned at the opposite sides of their fields of view. This research article thus provided a divergent view on the capabilities of deaf individuals, wherein their brain capabilities are actually still the same as normal individuals and are actually even more enhanced because they have acquired the capability of sensing visual motions of two different actions that are positioned at opposite sides of their field of view. This capability required a more sensitive reactivity which is not generally observed in individuals with normal hearing capabilities.
In another recent research article, Alary et al. (2008) described the capabilities of blind individuals in processing objects that are positioned in space. Their investigation showed that blind subjects are extremely adept in determining objects based on the sounds that are emitted by these objects. In addition, these individuals had the ability of determining their distance from the object through acoustic features that they sense. The investigators suggested that this interesting capability was acquired based on the absence of the participants’ sight and thus the occipital region of their brains were reassigned to performed other sensory functions that would help them to continue on with their daily routine. The occipital region is known to be responsible for the sensory function of sight in normal healthy individuals. In the case of blind individuals, the occipital region could not be used for seeing hence this region was rewired to perform for hearing, thus enhancing the auditory capabilities of blind individuals. The research also explained that the additional capacity of blind individuals was acquired during early childhood, yet other study participants also presented the same enhanced capabilities even when their eyesight was lost at a later stage in life. This observation thus showed that the occipital section of the brain plays an essential function in spatial positioning and determination of location.
Such remarkable capabilities observed from sensory deprived individuals may thus be explained through anatomical differences of the brain. In a study conducted by Ptito et al. (2008) involving magnetic resonance imaging (MRI) of the brains of visually impaired and normal individuals, it was observed that the geniculo-striate region of the brains of blind individuals underwent extreme atrophy, even reaching the optic nerves which were associated for seeing. In addition, the volume of this particular brain section was reduced by 25%, thereby significantly altering the capacity for vision. The corpus callosum brain regions of the blind individuals were also altered, indicating that these brain parts are definitely incapable of functioning for visual perception. However, the research described that the loss of function of these sections of the brain provided a mechanism for the human body to reorganize its neural connections in order to compensate for this particular sensory deprivation.
It has been reported by Fischer et al. (2007) that visually deprived individuals may still acquire their ability for vision. Earlier notions of visually impaired individuals staying blind for the rest of their lives are now proven wrong and this has been credibly shown in both humans and murine species. The research article describes that the visual cortex of mammals is highly plastic, wherein deprivation of sight of one eye from birth can still hold a chance for sight recovery. The reactivation of the eye was performed through the introduction of stimuli that would trigger the functioning of the eye. Interestingly, the researchers described that the same stimulation did not illicit a response from the normal eye. Such particular improvement in vision showed that the visual capacity of both humans and mouse models is thus impossible, given the correct type and degree of stimulation.
Conclusion
It should be noted that there are also individuals that experience deprivation of two sensory functions such as sight and hearing. In these individuals, the common etiology of dual sensory deprivation is genetic, injury or medical disorder. In addition, it has been observed that dual sensory deprivation afflicts individuals at any particular age and there is no susceptible age range that suffers from this defect, unlike other cases wherein an individual was born blind or deaf (Brennan and Bally, 2007). Hearing deprivation is significant in the life of an individual because this impedes the capacity of a person to communicate with the rest of the members of society. The condition also worsens because hearing impairment is strongly correlated with speech disabilities, rendering these individuals to experience difficulty in participating in social interactions. The existence of a second sensory deprivation thus magnifies that incapacity of an individual because it enhances their chances of performing routine tasks. The safety of individuals suffering from dual sensory deprivation is also a concern because not only do they not see the activities around them, but that they are also do not see any actions, things or people around them. The simple action of crossing a street thus seems like a major task for them because they are oblivious to the traffic lights and the sound of car horns or the ongoing traffic. As the dual impaired individual ages, his life also worsens because additional medical disorders commence, such as cardiovascular diseases that are strongly linked to the aging process. Analysis of the biopsychosocial condition of these individuals showed that they underwent extensive adaptations in their lifestyle and behavior in order to cope with the physical inadequacies. The administration of rehabilitation therapies also augmented the lives of these individuals and this resulted in a more complete perception of life.
Recent research reports thus have indicated that sensory deprivation generally results in the reassignment of functions of specific brain and neural connections in the body. Such reorganization provides an effective mechanism for an individual to adapt and adjust, based on the remaining functions that are normally functioning in the body. Such enhancement of other faculties may compensate for the deficit that has been deprived in an individual. It is thus possible that the brain is highly plastic and can rewire itself to acquire or enhance additional capabilities in order for the individual to survive and cope with his condition. Neurological and psychological analyses have further strengthened such observations, showing that the absence of a sensory function is replaced by the enhancement of another perceptual faculty.
References
- Alary, F., Goldstein, R., Duquette, M., Chapman, C.E., Voss, P. & Lepore, F. (2008). Tactile acuity in the blind: A psychophysical study using a two-dimensional angle discrimination task. Experimental Brain Research, 187,587–594.
- Brennan, M. & and Bally, S.J. (2007). Psychosocial adaptations to dual sensory loss in middle and late adulthood. Trends in Amplification, 11,281-300.
- Fischer,Q.S., Aleem, S., Zhou, H. & Pham, H.A. (2007). Adult visual experience promotes recovery of primary visual cortex from long-term monocular deprivation. Learning and Memory, 14,573-580.
- Nava, E., Bottari, D., Zampini, M. & Pavani, F. (2008). Visual temporal order judgment in profoundly deaf individuals. Experimental Brain Research, 190,179–188.
- Ptito, M., Schneider, F.C.G., Paulson, O.B. & Kupers, R. (2008). Alterations of the visual pathways in congenital blindness. Experimental Brain Research, 187,41–49.