The subcortical structures come into play when one feels that they are under threat or in a dangerous situation. When fear is induced in an individual numerous hormones are released that send information to the amygdala – which in turn, trigger what is know as the ‘fight or flight’ response. It is thought that there are two distinct pathways in the fear system, which are the cortical pathway, and the subcortical pathway (Datta, 2006). To find out if all processing in the subcortical system is unconscious one could look at the cortical system which is thought to be the more rational part of the conscious pathway in response to a ‘fight or flight’ situation. Both, the cortical and the subcortical pathways are linked to the visual structures of the brain; the former being more ‘direct’ and using the visual cortex and the latter being ‘indirect’ but still using the visual system. Understanding why there are two fear systems and the processes of these systems will give a better insight into whether all processing carried out by the subcortical system is strictly an ‘indirect’ and unconscious process. One should bear in mind that unconsciousness is tricky to study because it is subjective to the individual. If one is asked to perform a task in an unconscious state they will consciously be aware of trying to reach that unconscious state.
The subcortical system is dubbed the dirty pathway due to fact it sends less information about stimuli from the visual sensory input to the thalamus, and then the amygdala without any rationalisation from the individual due to it being processed unconsciously (Datta, 2006). Consequently, working almost instantaneously, this could facilitate a life saving response by individual, but on the other hand, it could also create an inappropriate response to harmless stimuli due to lack of reasoning. Conversely, the more conscious cortical pathway can add a delay somewhere in the region of one hundred to five hundred milliseconds (Datta, 2006). This is due to the cortical system consciously sending more information about visual stimuli from the visual sensory input to the thalamus, then to the visual cortex, and finally to the amygdala (Datta, 2006). By the time the conscious and more rational cortical system has kicked in the individual has already reacted unconsciously to the affects of the subcortical system. The possible explanation of the purpose of the cortical pathway could be so that the individual can gauge the situation in a more rational manner in the event that danger is still in play and act accordingly in the environmental settings. Thusly, it could also help with emotional responses to fearful and dangerous situations. Both pathways might work synergistically, or one pathway may set off the other. Looking at studies and experiments of visual face masking and also visual blindsight can help gain a better understanding of these different pathways.
An experiment was carried out to test whether participants would react to subliminal pictures of different emotive faces and how this would subsequently affect their reaction afterwards. Happy, angry and neutral faces where displayed for sixteen milliseconds and then a neutral face was finally shown for 400 milliseconds. The patients were asked to perform an unrelated task. How they responded to the task was wholly dependent on which subliminal picture they had seen. Subsequently, the participants had emotionally engaged with the different emotions of the subliminal photos unconsciously. Essentially what this indicates is that, what they saw visually – which was a neutral face – did not correspond to the emotional engagement that they were subjected to unconsciously. Also, similar studies on patients with lesions to the primary visual cortex (V1) have shown similar results. Thusly, these have shown that individuals with a blind field of vision still have an unconscious visual function and are able to point to and describe objects in their blind field of vision. This has led to the phenomenon being called affective blindsight. Henceforth, it could be possible that visual processing is separate from conscious awareness. Furthermore, It has been suggested that the subcortical pathway processes visual information independently of the cortical face processing areas that are necessary of conscious awareness (Morris, Ohman & Dolan, 1999).
To conclude, the subcortical system mediates the cortical system and this separates visual processing from conscious awareness. It could be said that the subcortical pathway is processed unconsciously as it sends information to the amygdala and the cortical pathway is processed consciously. This would make sense in an evolutionary aspect as fight or flight situations with any slight delay could mean life or death tactics. There is evidence that backs these claims, but one must be aware that lesions in brain-damaged patients are different in every case study and there are different changes and neural processes after damage. Therefore continued study in this area would be beneficial.
Datta, S. (2006) ‘Introduction to Brains, Mind and Consciousness’, in Bearman, G., Graham, R., Riley, G. & Wardell, P. (eds) From Cells To Consciousness, pp. 140 – 57, The Open University.
Morris, J.S., Ohman, A., and Dolan, R.J. (1998). Conscious and unconscious emotional learning in the human amygdala. Nature, 393, 467-470.