Agnosia in Canon: a Historical Issue

Agnosia is defined as a neurologic disorder through which the patient loses the ability to recognize persons, objects, shapes or sounds depending on the sense involved whereas the sense might not be defective and there might not be any memory loss (1). Chronologically, agnosia was first described by Carl Wernicke (1874) and Kuss-maul (1877) who tried to respectively explain receptive aphasia and word deafness via agnosia (2). Searching the Cannon of Avicenna (3), the author found that the book has elaborately described this neurologic phenomenon. Describing disorders resulting from imagination damages, Avicenna classifies the disorders as failure, disability, deterioration and exuding the norms. He further defines failure as a perceived sense that disappears and a veil of forgetfulness comes between mind and sense. In order to have a better understanding of the said definition, we should first find out what he means by imagination. Avicenna's explanation of imagination in Cannon is very interesting. He believes imagination keeps senses after coming together and preserves them in the absence of feelings. Therefore, imagination is different from panesthesia because the latter is the power that perceives senses and imagination make them occur even in the absence of senses. Avicenna provides a more precise definition of the how's of our relationship with the outside world that forms through senses. The senses are perceived by panesthesia but imagination has the capacity of preserving what is sensed even in the absence of the sensed object. In other words, imagination keeps feelings in mind. Imagination is not a fictitious entity; yet, the empirical view of Avicenna can define it physiologically. He believes that imagination is one of the actions of the brain, i.e. we can understand different states of brain through actions like imagination. So, it can be said that brain actions are actually brain functions like seeing, hearing, memorizing, etc. and as it was previously mentioned, Avicenna distinguishes sensing from keeping senses in mind. He mentions that failure of senses might not occur due to their disorder, but might be the result of a disorder in the brain. It means sense organs like eye, ear or skin may not be defective but an individual may have a problem with his senses. According to Avicenna, the disturbance happens in the brain. It is interesting that failure of senses is sub-categorized as sensory actions and Avicenna has separated it from imagination disturbance. This difference can be important for …