A number of symptoms of Alzheimer’s disease are labeled as "psychotic," hallucinations being one of them. Around 18 percent of people with Alzheimer’s disease experience hallucinations, and they are more often reported in people with a later disease onset. For the majority these are visual, for others they are auditory, with some having both. Experiencing hallucinations normally lasts from one to two years and occurs in line with declining cognitive functions.
Lewy Bodies
Alzheimer’s disease brains show disc-shaped plaques outside brain cells called neurons, and neurofibrillary tangles inside them. However, there is debate about whether these are the cause of hallucinations. There is better linkage between hallucinations and "Lewy Bodies," round masses inside neurons. Debbie Tsuang, in the American Journal of Geriatric Psychiatry's April 2009 edition, found these in nearly 2/3 of patients with visual hallucinations. A review by Antony Harding in the February 2002 edition of Brain, detailed how Lewy Bodies were shown in brain areas affected by Alzheimer’s disease, such as the hippocampus and amygdala, which are involved in emotional interpretation. Lewy Bodies are more often seen in Parkinson’s disease and dementia with Lewy Bodies--where hallucinations are one symptom. Harding suggests people with Alzheimer’s disease with hallucinations may also have one of these disorders.
The Occipital Lobe
The occurrence of visual hallucinations is not related to defects in the eyes or retinal connections to the brain, although visual problems may exacerbate hallucinations. Shu-Han Lin discusses in the November-December 2006 edition of Clinical Imaging how instead hallucinations are associated with a decreased occipital lobe, which is involved in visual interpretation. This has led some, including Suzanne Holroyd in the Journal of Neuropsychiatry and Clinical Neurosciences Winter 2000 edition to propose that hallucinations are due to damage to brain regions involved in vision and those that interpret visual signals, including the occipital lobe, the amygdala and the hippocampus.
Genes
APOE4 is one form of the gene for the protein apolipoprotein E, normally involved in neuronal functioning. APOE4 is found in around 15 percent of people and causes functional problems with apolipoprotein E, leading to an eight-fold risk for developing Alzheimer’s disease. Study results are mixed regarding whether APOE4 is involved in the development of hallucinations. While the Tsuang study above didn’t find an association, another, by Kristina Zdanys in Neuropsychopharmacology's January 2006 edition, found APOE4 associated with an increased risk of “visual disturbances.”
Another gene possibly involved in hallucinations is for the protein brain-derived neurotrophic factor, or BDNF, which is involved in dynamic neuronal changes. There are decreased amounts of BDNF in Alzheimer’s disease, in line with disease severity. One form of the BDNF gene was reported by Kristina Zdanys in the Journal of Alzheimers Disease July 2009 edition to be significantly linked to increased occurrences of hallucination.
A third gene is for one of the neuronal receptors for the brain neurochemical serotonin, called 5HT2A. Stimulation of this receptor can cause hallucinations, and a study by Antonia Pritchard in Neurobiology of Aging's March 2008 edition found a small association between hallucinations and one form of the 5HT2A receptor.
References
- "American Journal of Psychiatry"; Epidemiology of and Risk Factors for Psychosis of Alzheimer's Disease: A Review of 55 Studies Published From 1990 to 2003; Susan Ropacki and Dilip Jeste; November 2005
- "American Journal of Geriatric Psychiatry"; Visual Hallucinations in Dementia: A Prospective Community-Based Study with Autopsy; Debby Tsuang et al; April 2009
- "Brain"; Visual Hallucinations in Lewy Body Disease Relate to Lewy Bodies in the Temporal Lobe; Antony Harding et al; February 2002
- "Clinical Imaging"; The Occipital White Matter Lesions in Alzheimer's Disease Patients with Visual Hallucinations; Shu-Han Lin et al; Nov.-Dec. 2006
- "Journal of Neuropsychiatry and Clinical Neurosciences"; Occipital Atrophy is Associated with Visual Hallucinations in Alzheimer's Disease; Suzanne Holroyd et al; Winter 2000
