Unfortunately, there is little published scientific literature that specifically addresses the impact of gentamicin poisoning on concentration or memory, although a very common complaint of gentamicin poisoning victims is a frustrating lack of concentration and ability to plan and carry out complex tasks, coupled with short-term memory loss.
According to the Vestibular Disorders Association, the cognitive and psychological symptoms of vestibular disorders can include:
- Difficulty concentrating and paying attention; easily distracted
- Forgetfulness and short-term memory lapses
- Confusion, disorientation, difficulty comprehending directions or instructions
- Difficulty following speakers in conversations, meetings, etc., especially when there is background noise or movement
- Mental and/or physical fatigue out of proportion to activity
- Loss of self-reliance, self-confidence, self-esteem
- Anxiety, panic
Dr. Timothy Hain, a neurologist at Northwestern University in Chicago who has studied balance disorders and gentamicin ototoxity extensively, notes on his website:
Many people with bilateral vestibulopathy complain of a mild confusion or "brain fog", which is attributed to the increased attention needed to maintain balance and good vision, due to loss of vestibular input. Others call it "inability to multi-task". It is thought that in persons with bilateral vestibular loss, the ongoing extra effort needed to keep ones balance reduces the amount of attention that is available for other thinking tasks. Considerable evidence for this can be found in the recent literature (Andersson et al, 2003; Pellecchia, 2003; Redfern et al, 2003). Persons with other vestibular disorders often complain of difficulty concentrating and mental fatigue (Yardley et al. 1998).
Complete web page here.
The references he cites are set forth below:
Anderson G and others. Dual-Task study of cognitive and postural interference in patients with vestibular disorders. Otol Neurotol 24:289-293, 2003. Abstract
Pellechia GL. Postural sway increases with attentional demands of concurrent cognitive task. Gait and Posture 18(2003), 29-34 Abstract
Redfern MS and others, Cognitive influences in postural control of patients with unilateral vestibular loss. Gait and Posture, 2003, Abstract
Yardley L, Burgneay J, Nazareth I and Luxon L (1998). "Neuro-otological and psychiatric abnormalities in a community sample of people with dizziness: a blind, controlled investigation." J Neurol Neurosurg Psychiatry 65(5): 679-84. Abstract
In my medical-legal review of over 70 cases of gentamicin ototoxicity, I believe that at least 85-90% of these clients reported some form of concentration or memory problems secondary to gentamicin administration. It is often the most frustrating aspect of gentamicin poisoning: persons who had skilled desk jobs, or who were professionals that did not require much in the way of physical activity to perform their jobs could no longer function at work in any meaningful capacity. Persons who once prided themselves on being very organized and remembering everything could not remember what was told them 5 minutes before, or what they had just read.
The most simplistic explanation for lack of concentration and short-term memory loss is that the brain of a person suffering from gentamicin poisoning is totally overloaded with keeping the body upright and functioning in 3 dimensional space.
Although not sufficient to conclusively prove that the oscillopsia and balance disorder associated with gentamicin ototoxicity affects cognitive function, the following studies are supportive of the notion in general.
Yardley L, Papo D, Bronstein A, Gresty M, Gardner M, Lavie N, and Luxon L. Attentional demands of continuously monitoring orientation using vestibular information. Neuropsychologia. 2002;40(4):373-83 Abstract
A study has demonstrated specific neurochemical changes to the hippocampus, a portion of the brain directly associated with memory, when rat vestibular systems have been destroyed. (Zheng Y, Horii A, Appleton I, Darlington CL, and Smith PF. Damage to the vestibular inner ear causes long-term changes in neuronal nitric oxide synthase expression in the rat hippocampus. Neuroscience. 2001;105(1):1-5. Abstract )
When rats were given a bilateral labyrinthectomy (a surgical procedure which destroys the vestibular system of the inner ear, just as gentamicin does), a long term deficit in object recognition occurred. This is very supportive of the notion that vestibular information may contribute to non-spatial memory to some extent, and that lack of vestibular information directly causes a deficit in non-apatial memory. (Zheng Y, Darlington CL, and Smith PF. Bilateral labyrinthectomy causes long-term deficit in object recognition in rat. Neuroreport. 2004 Aug 26;15(12):1913-6. Abstract)