Associative hallucinations result from stimulating left ventromedial temporal cortex

Abstract

Visual recognition requires connecting perceptual information with contextual information and existing knowledge. The ventromedial temporal cortex (VTC), including the medial fusiform, has been linked with object recognition, paired associate learning, contextual processing, and episodic memory, suggesting that this area may be critical in connecting visual processing, context, knowledge and experience. However, evidence for the link between associative processing, episodic memory, and visual recognition in VTC is currently lacking. Using electrocorticography in a single human patient, medial regions of the left VTC were found to be sensitive to the contextual associations of objects. Electrical brain stimulation of this part of the left VTC of the patient, functionally defined as sensitive to associative processing, caused memory related, associative visual hallucinations. This provides evidence of a relationship between visual recognition, associative processing, and episodic memory. These results suggest a potential role for abnormalities of these processes as part of a mechanism that gives rise to some visual hallucinations.

The Effects of Tryptamine Psychedelics in the Brain: A meta-Analysis of Functional and Review of Molecular Imaging Studies

“…These complex forms of hallucinogen-induced hallucination and visions, also lead the recruitment of higher level regions in the brain, given that psychedelic imagery is usually very structured, thematic and personal ( Kraehenmann, 2017 ). In accordance to our main results, studies have reported visual hallucinations caused by neuronal stimulation of PFC ( Blanke et al, 2000 ), temporal areas ( Mégevand et al, 2014 ; Aminoff et al, 2016 ) and increased functional connectivity between PFC and primary visual cortex ( Carhart-Harris et al, 2016b ). Furthermore, the review conducted by dos Santos et al (2016) , suggested that hallucinogens increase introspection and positive mood by modulating brain activity in the fronto-temporo-parieto-occipital cortices.…”

Insights into human cognition from intracranial EEG: A review of audition, memory, internal cognition, and causality

“…Relevant to memory (section 3), Aminoff and colleagues observed that stimulation of ventromedial temporal cortex, part of the ventral visual stream involved in object perception, elicited memoryrelated, visual hallucinations of objects that had been previously associated [173]. Indeed, studies of Penfield in the 1960s reported that intracranial stimulation of temporal cortex activated visual and auditory memory representations of past experiences [174], replicated in [175].…”

Dreams and Psychedelics: Neurophenomenological Comparison and Therapeutic Implications

“…However, contrary to the notion that psychedelic-induced visual hallucinations are caused by bottom-up driven neuronal activity, there is substantial evidence that psychedelics induce visual hallucinations primarily via neuronal activation of prefrontal cortical or temporal areas as well as top-down spreading of activation to parietal and primary visual regions – a mechanism that is also underlying visual mental imagery [ 82 - 84 ]: 1. classic psychedelics produce their effects primarily via activation of postsynaptic cortical serotonin 2A (5-HT2A) receptors on pyramidal neurons in layer V of the prefrontal cortex (PFC), leading to glutamate-dependent downstream activity changes [ 85 ]; 2. visual hallucinations may be caused by neuronal stimulation of PFC [ 86 ] or temporal lobe [ 37 , 87 ], and spreading activation to primary visual cortex; and 3. psychedelic hallucinations are related to increased functional connectivity between PFC and primary visual cortex [ 79 ], indicating that psychedelic hallucinations substantially depend on PFC regions, and not solely on primary visual regions. A third explanatory model for psychedelic hallucinations would be a mixed bottom-up/top-down model, where visual noise is fed into higher-level areas, which then interpret and make sense of the noise [ 88 ].…”