Research Officer, National Health and Medical Research Council (NHMRC), Visual and Cognitive Neuroscience Laboratory, Department of Optometry & Vision Sciences and Mel-bourne Brain Centre, University of Melbourne, Parkville, Vic 3010, AustraliaAustralia
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Our perception of vision is largely as a result of the signals conveyed from the eye to the brain via the retino-thalamo-cortical pathway. Visual signals within this pathway originate from three cone photoreceptors (responsible for day vision) and one scotopic receptor, the rods. The cones are classified according to their spectral sensitivity peaks as Long(L), Medium(M) and Short(S) wavelength sensitive cones. Our chromatic perception is dependent upon how the brain processes variations in the activity among these photoreceptors. Chromatic signals are generally thought to be processed by two parallel streams, the red-green system by the parvocellular system1,2 and the blue-yellow system by the koniocellular system.3,4 A large body of work has already been documented to identify these streams within the retina and the main thalamic visual nucleus, the Lateral Geniculate Nucleus (LGN). However, our knowledge about the processing of the chromatic signal within the visual brain, particularly the pathways taken by the blue-yellow colour signals within the brain is at its infancy
Keywords: Geniculate; koniocellular; parvocellular
NEURO ISSN 2377-1607 http://dx.doi.org/10.17140/NOJ-2-e002 Open Journal Editorial Blue Cone Signals in the Extra Striate * *Corresponding author Cortex: Explanation for Blind Sight?
Jaikishan Jayakumar, PhD Research Officer National Health and Medical Research * Council (NHMRC) Jaikishan Jayakumar Visual and Cognitive Neuroscience Laboratory Research Officer, National Health and Medical Research Council (NHMRC), Visual and Department of Optometry & Vision Sciences and Melbourne Brain Centre Cognitive Neuroscience Laboratory, Department of Optometry & Vision Sciences and Mel- University of Melbourne bourne Brain Centre, University of Melbourne, Parkville, Vic 3010, Australia Parkville, Vic 3010, Australia E-mail: jja@unimelb.edu.au Our perception of vision is largely as a result of the signals conveyed from the eye to Volume 2 : Issue 1 the brain via the retino-thalamo-cortical pathway. Visual signals within this pathway originate Article Ref. #: 1000NOJ2e002 from three cone photoreceptors (responsible for day vision) and one scotopic receptor, the rods. The cones are classified according to their spectral sensitivity peaks as Long(L), Medium(M) Article History and Short(S) wavelength sensitive cones. Our chromatic perception is dependent upon how the th brain processes variations in the activity among these photoreceptors. Chromatic signals are Received: July 10 , 2015 th generally thought to be processed by two parallel streams, the red-green system by the parvo- Accepted: July 10 , 2015 th 1,2 3,4 Published: July 13 , 2015 cellular system and the blue-yellow system by the koniocellular system. A large body of work has already been documented to identify these streams within the retina and the main tha- lamic visual nucleus, the Lateral Geniculate Nucleus (LGN). However, our knowledge about Citation the processing of the chromatic signal within the visual brain, particularly the pathways taken Jayakumar J. Blue cone signals in the by the blue-yellow colour signals within the brain is at its infancy.
extra striate cortex: explanation for blind sight? Neuro Open J. 2015; 2(1): e2-e3. doi: 10.17140/NOJ-2-e002 Majority of relay cells within the LGN project to the primary Visual cortex (V1) and hence is considered vital for our visual perception. However, in some clinical cases, even after extensive damage to V1, patients have some residual vision. This phenomenon is called 5,6 “blind sight”.5,6 The patients usually exhibit little or no awareness of visual stimuli, however can perform tasks that seemingly needs vision such as navigation. Most common hypothesis that has been postulated explaining this phenomenon is that blindsight is mediated by inputs 7,8 to middle temporal area or area MT that bypass V1.7,8 Area MT remains active even after com- 9 10 plete ablation9 or reversible inactivation10 of V1, suggesting that there are alternative pathways that bypass V1 to reach MT. Experiments with inactivation of the superior colliculus showed that one such pathway exists via the colliculus.11 Whether there is any evidence that blindsight is made up of chromatic signals is still unresolved. The perception of colour is usually associ- ated with the “what” pathway as evident from area V412 often considered to be the area that processes color information and for being the gateway to the ventral pathway. Area MT, an extrastriate visual area is considered to be part of the “ where” pathway and until recently was not considered to receive any colour signals but see Conway13 for a review of color signals in 14,15 the dorsal and ventral pathways. However, more recent studies have shown that this area 15 16 receives robust chromatic signal not only via V1 but also bypassing V1.15 Other studies16 have also shown that in subjects with blindsight found that within the hemianopic field, S-cone modulating stimuli were very effective in eliciting visual performance, and in fact in one pa- tient presentation of narrow band blue stimuli (427 nm) led to excellent performance but not red stimuli (peaking at 630 nm). Thus, there is increasing evidence that S-cone signals reach Copyright area MT via a more direct route that bypasses V1 and providing an alternate explanation of ©2015 Jayakumar J. This is an blindsight in humans.
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