Repeated visual hallucinations in Parkinson's disease as disturbed external/internal perceptions: Focused review and a new integrative model

Abstract

Visual hallucinations (VH) in Parkinson's disease (PD) are a chronic complication in 30 to 60% of treated patients and have a multifaceted phenomenology. Flickering, faultive impressions, and illusionary misperceptions precede the core syndrome of stereotyped, colorful images. The patient variably recognizes these images as hallucinations, being rarely irritated or frightened and more often amused as a bystander. Although studies on VH in PD focus on several research domains, no comprehensive, unified theory has been developed to study their pathophysiology. We have adapted Hobson's work on the states of consciousness and propose a model integrating seemingly disparate data on VH. We suggest that VH should be considered as a dysregulation of the gating and filtering of external perception and internal image production. Contributive elements and anatomical links for the model include poor primary vision, reduced activation of primary visual cortex, aberrant activation of associative visual and frontal cortex, lack of suppression or spontaneous emergence of internally generated imagery through the ponto-geniculo-occipital system, intrusion of rapid eye movement dreaming imagery into wakefulness, errative changes of the brainstem filtering capacities through fluctuating vigilance, and medication-related overactivation of mesolimbic systems. Different etiologies likely produce different phenomenologies and the prognosis may not be uniform. This new conceptual framework permits an anatomical view of VH and suggests new, testable hypotheses regarding their pathophysiology and therapy.

Visual Hallucinations in PD and Lewy Body Dementias: Old and New Hypotheses

“…Various descriptions report inanimate objects (leaves on the wall) [48], animated figures (children playing) [48], normal size figures [16,17,49,50], miniature people and animals [45,51], images from daily life experience [16,52], and images from TV programs [16].…”

“…One model described by Diedrich et al [49] encompassed the occurrence of VH inside Hobson's schemata of mental states [121] where states of cerebral activity are schematised in the so-called Activation-Input Source-Modulation (AIM) model. Activation reflects the rate at which the mind can process information, input source is a measure of the level to which the brain processes external sensory data (in waking) or internal perception or information and modulation is the ratio of aminergic (noradrenergic and serotoninergic) predominance in waking to cholinergic predominance in REM sleep.…”

Visual Priming and Visual Hallucinations in Parkinson’s Disease. Evidence for Normal Top-Down Processes

“…2 A second model has proposed that poor visual input and processing in combination with defective central visual monitoring produces partial visual deprivation. 4 Hence, visual input cannot be interpreted, allowing the deblocking of visual memory contents as a release phenomenon. 4 A third model has hypothesized that VH in PD were due to an inability to recruit the visually mediated dorsal attentional network in the presence of ambiguous percepts, leading to an overreliance on networks such as the default node network to interpret the stimuli.…”

Haliucinacijų etiologijos aspektai

“…Neretai regos haliucinacijoms būdingas "prodromo sindromas", kuomet ligoniai jaučia kažkieno buvimą kambaryje, už nugaros, judėjimą periferijoje, taip pat patiria miego sutrikimus, sapnuoja itin ryškius sapnus. Yra iškelta keletas galimų priežasčių, kodėl vystosi regos haliucinacijos: ilgalaikio dopamino agonistų ir levodopos sukeltas šalutinis poveikis, neuronų, sekretuojančių acetilcholiną, hipofunkcija, serotoninerginių neuronų disfunkcijos (12). Regos haliucinacijos taip pat gali vystytis pagal štai tokią schemą: 1) sumažinamas ir supaprastinamas informacijos apie esamą aplinką kiekis, 2) sutrikęs vidinis gebėjimas stebėti aplinką, 3) silpstanti atmintis, 4) panaudojamos schemos ir vaizdai iš vis dar egzistuojančių prisiminimų ir atminties, kurie tariamai galė-tų užpildyti matomų, tačiau nesuvokiamų dalykų spragas, todėl ligoniams sunku diferencijuoti, ar vaizdas kilo esant aplinkos, ar vidiniam dirginimui (13).…”