Activation of striate cortex in the absence of visual stimulation: an fMRI study of synesthesia

Alemán, André; Rutten, Geert‐Jan; Sitskoorn, Margriet M.; Dautzenberg, Géraud; Ramsey, Nick F.

doi:10.1097/00001756-200109170-00015

Cited by 56 publications

(37 citation statements)

References 13 publications

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“…Increased GM for projectors compared with associators was also found in superior precuneus cortex. Increased activation in V1 has previously been found only in a case study (Aleman et al, 2001); unfortunately it is not clear whether this particular female with colored-hearing had projector-type experiences. The current finding of increased GM in V1 is in line with the notion of Ward et al (2007) that the defining feature of projectors is binding of color to the location of an object in external space.…”

Section: Projector Synesthetesmentioning

confidence: 76%

“…Previous studies found activation of prefrontal brain areas during synesthesia (Paulesu et al, 1995;Schiltz et al, 1999;Aleman et al, 2001;Nunn et al, 2002;Sperling et al, 2006;Beeli et al, 2008). One possible explanation is that prefrontal and modality-specific brain areas interact in creating the synesthetic experiences.…”

Section: Projector Grapheme-color Synesthesiamentioning

confidence: 93%

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Neural Basis of Individual Differences in Synesthetic Experiences

Rouw¹,

Scholte²

2010

J. Neurosci.

126

146

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Little is known about how the properties of our private mental world relate to the physical and functional properties of our brain. Studying synesthesia, where a particular experience evokes a separate additional sensory experience, offers the unique opportunity to study phenomenological experiences as a stable trait in healthy subjects. A common form of synesthesia is grapheme-color synesthesia, where a particular letter or number evokes a particular color experience. We studied the neural basis of qualitative different properties of the synesthetic experience by using individual differences in grapheme-color synesthesia. Specifically, the synesthetic color can be experienced "in the mind" (associator synesthetes) or "in the outside world" (projector synesthetes). Gray matter structure and functioning (imaged using voxel-based morphometry and functional magnetic resonance imaging, respectively) were examined in grapheme-color synesthetes (N ϭ 42, 16 projectors and 26 associators) and nonsynesthetes. Results indicated partly shared mechanisms for all grapheme-color synesthetes, particularly in posterior superior parietal lobe, which is involved in the integration of sensory information. In addition, the nature of synesthetic experience was found to be mediated by distinct neural mechanisms. The outside-world experience is related to brain areas involved in perceiving and acting in the outside world (visual cortex, auditory cortex, motor cortex) as well as frontal brain areas. In contrast, the in-the-mind experience is related to the hippocampus and parahippocampal gyrus, known for their role in memory. Thus, the different subjective experiences are related to distinct neural mechanisms. Moreover, the properties of subjective experiences are in accordance with functional properties of the mediating brain mechanisms.

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Section: Projector Synesthetesmentioning

confidence: 76%

Section: Projector Grapheme-color Synesthesiamentioning

confidence: 93%

Neural Basis of Individual Differences in Synesthetic Experiences

Rouw¹,

Scholte²

2010

J. Neurosci.

126

146

View full text Add to dashboard Cite

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“…Similarly, in a case study of a synesthete who experiences colors for people's names, Weiss et al [40] report that hearing names that elicited synesthetic colors led to activity in left extra-striate cortex (near to V4), but not V1. However, in another case study of an auditory word → color synesthete, Aleman et al [41] report activation of (anatomically defined) primary visual cortex but were unable to determine if area V4 was active in this single subject. I return to potential statistical and methodological reasons for some of these differences below.…”

Section: Word → Color Synesthesiamentioning

confidence: 87%

Neurophysiology of synesthesia

Hubbard

2007

Curr Psychiatry Rep

102

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[150 words]Synesthesia is an experience in which stimulation in one sensory or cognitive stream leads to associated experiences in a second, unstimulated stream. Although synesthesia is often referred to as a "neurological condition", is not listed in the DSM-IV or the ICD classifications, since it generally does not interfere with normal daily functioning. However, its high prevelance rate (1 in 23) means that synesthesia may be reported by patients who present with other psychiatric symptoms. In this review, I focus on recent research examining the neural basis of the two most intensively studied forms of synesthesia, grapheme → color synesthesia and tone → color synesthesia. These data suggest that these forms of synesthesia are elicited through anomalous activation of color selective areas, perhaps in concert with hyper-binding mediated by the parietal cortex. I then turn to questions for future research, and the implications of these models for other forms of synesthesia.

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“…Synaesthesia is automatic and consistent throughout life, and on the surface seems to be a case of feature binding that does not require attention. Functional imaging studies have shown that areas within the ventral pathway that normally register shape, colour and words are activated in synaesthetes, but in addition, there is also parietal activity, which for the most part has been downplayed [67][68][69] . Some have argued that the automaticity and consistency of the synaesthetic experience represent direct connections between cortical feature maps 13 , perhaps through synaptic connections that fail to undergo normal synaptic pruning during development 70,71 .…”

Section: Synaesthetic Bindingmentioning

confidence: 99%

Binding, spatial attention and perceptual awareness

2003

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The world is experienced as a unified whole, but sensory systems do not deliver it to the brain in this way. Signals from different sensory modalities are initially registered in separate brain areas -even within a modality, features of the sensory mosaic such as colour, size, shape and motion are fragmented and registered in specialized areas of the cortex. How does this information become bound together in experience? Findings from the study of abnormal binding -for example, after stroke -and unusual binding -as in synaesthesia -might help us to understand the cognitive and neural mechanisms that contribute to solving this 'binding problem'.Different areas of the cortex receive sensory information through different receptors (for example, the eyes, ears or touch receptors), showing that different areas of the cortex respond to different features of the sensory mosaic. Investigations of multimodal integration have a long history, but a particularly interesting binding problem arose when reliable evidence began to emerge that, within the brain, different areas are specialized for encoding different features of the visual modality, such as colour, shape, size and motion in vision 1 . Electrophysiological recordings from monkey cortices showed that visual neurons in different areas responded with different strengths to different features 2 . This specialization has received support from functional imaging studies in humans 3 . Moreover, this evidence is consistent with more than a hundred years of neuropsychological reports that lesions in different areas of the human brain can result in relatively isolated deficits in visual processing -for example, ACHROMATOPSIA or visual NEGLECT 4,5 . This modular organization of the brain led to the question of how features that are registered separately are reunited to produce our unified experience of the world 6,7 . Some researchers have argued that this type of 'binding problem' is not a problem at all 8,9 , but recent evidence has shown that it can become a real problem in everyday life when certain areas of the brain are no longer functioning 10 .In this review, I will discuss evidence -from both normal perceivers and neurological patients -that binding features within vision is a problem in humans, and is not just a theoretical construct. I will then describe the role that spatial attention is believed to have in this type of binding, emphasizing the spatial functions of the parietal lobes 11 . Finally, I will explore how binding might change if two or more specialized FEATURE MAPS were to merge. This final issue has been approached within a cognitive neuroscience perspective by testing shape/colour synaesthetes -otherwise normal individuals who perceive internally generated colours (induced by particular visual shapes) as if they were being received by sensory receptors (so that the colours are perceived as 'out there') 12 . For instance, the letter A might induce a certain shade of blue. It has been hypothesized that synaesthesia results from developmentally a...

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Activation of striate cortex in the absence of visual stimulation: an fMRI study of synesthesia

Cited by 56 publications

References 13 publications

Neural Basis of Individual Differences in Synesthetic Experiences

Neural Basis of Individual Differences in Synesthetic Experiences

Neurophysiology of synesthesia

Binding, spatial attention and perceptual awareness

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