Posts Tagged ‘perception’

Investigating the Anatomical Relationship Between Primary Sensory and Prefrontal Cortices in the Human Brain

11/10/2011 1 comment

People experience the world in slightly different ways. Philosophers have been writing about this for years and, recently, studies using psychophysics and neuroimaging provide further support for this. A classic example is the way we perceive visual illusions; there is variability in the responses of people about the extent they experience various illusions. Schwarzkopf et al. (2010) showed that inter-individual differences in the surface area of V1 predict individual differences in conscious perception, such as how big something looks.

A study by Chen et al. that was published on the  JoN used a novel approach that combined non-invasive cortical functional mapping with whole-brain voxel-based morphometric analyses to investigate the anatomical relationship between the functionally mapped visual cortices and other cortical structures in healthy humans. Chen et al. found an interesting correlation between the size of V1 and primary auditory cortex. This relationship could be explained in terms of our everyday multisensory experience of the world. However, the size of those areas was anticorrelated with the size of the anterior prefrontal cortex (aPFC), the frontopolar part of the frontal cortex. In a few words, individuals with larger primary visual cortex had larger primary auditory cortex but smaller aPFC. This anticorrelation was only found for the primary sensory cortices and not for other visual cortices (e.g. V2, V3).

According to Chen et al.

…while one might expect a positive correlation between the whole-brain gray matter volume and the volume of its components, instead we found a striking anticorrelation for primary visual cortex: individuals with larger brains tended to have smaller primary visual cortices. In contrast, anterior prefrontal cortex was the single most enlarged region in a larger brain.

The aPFC is a particularly fascinating area. Apart from having many names (anterior PFC, the frontal pole, frontopolar cortex, rostral prefrontal cortex, BA 10…), aPFC is larger relative to the rest of the brain (Semendeferi et al., 2001) and is significantly different in humans compared to other primates (Semendeferi et al., 2001), suggesting that this region may contribute to the unique human behaviour. Furthermore, it is one of the last brain areas to mature in humans (Dumontheil et al., 2008) and has been recently identified as the region with the greatest relative prediction power about brain maturity over development (Dosenbach et al., 2011). Evidence from previous studies suggest that this particular area has a role in higher-order cognitive functions (including prospective memory)

The pairing between the expansion of anterior prefrontal cortex and the contraction of primary sensory cortices reflects a common ground for the formation of anatomically and phylogenetically remote cortical regions, and suggests the existence of a reciprocal link between high-order cognition and low-level sensation.

Future studies will attempt to further investigate this relationship and examine what the effects of these structural differences are on function and performance on various tests thought to tap on those areas.

ResearchBlogging.orgSong C, Schwarzkopf DS, Kanai R, & Rees G (2011). Reciprocal anatomical relationship between primary sensory and prefrontal cortices in the human brain. The Journal of neuroscience : the official journal of the Society for Neuroscience, 31 (26), 9472-80 PMID: 21715612

Schwarzkopf DS, Song C, & Rees G (2011). The surface area of human V1 predicts the subjective experience of object size. Nature neuroscience, 14 (1), 28-30 PMID: 21131954

Coren S, & Porac C (1987). Individual differences in visual-geometric illusions: predictions from measures of spatial cognitive abilities. Perception & psychophysics, 41 (3), 211-9 PMID: 3575080

Dumontheil I, Burgess PW, & Blakemore SJ (2008). Development of rostral prefrontal cortex and cognitive and behavioural disorders. Developmental medicine and child neurology, 50 (3), 168-81 PMID: 18190537

Semendeferi, K., Armstrong, E., Schleicher, A., Zilles, K., & Van Hoesen, G. W. (2001). Prefrontal cortex in humans and apes: a comparative study of area 10 American journal of physical anthropology, 3 (114), 224-241

Dosenbach NU, Nardos B, Cohen AL, Fair DA, Power JD, Church JA, Nelson SM, Wig GS, Vogel AC, Lessov-Schlaggar CN, Barnes KA, Dubis JW, Feczko E, Coalson RS, Pruett JR Jr, Barch DM, Petersen SE, & Schlaggar BL (2010). Prediction of individual brain maturity using fMRI. Science (New York, N.Y.), 329 (5997), 1358-61 PMID: 20829489

Blindsight: The Blind Man Who Can See..

Blindsight is rare and strange condition. People suffering from blindsight respond to visual stimuli without consciously perceiving them.  V. S. Ramachandran has an interesting theory about this:

Interesting links:

Short clip from Beatrice de Gelder’s famous Blindsight study
Blind, Yet Seeing: The Brain’s Subconscious Visual Sense – article
Seeing What You Don’t See
Mystery of “Blindsight” Lets Some Blind People “See,” Study Shows – National Geographic
Blindsight and Consciousness
Blindsight in monkeys
Blindsight revisited (pdf)

Does time really slow down during frightening events?

Overestimation of time duration is often reported during brief, dangerous or possibly life threatening events, like car accidents, robberies or attacks. Observers mention that time feels like slowing down and everything seems to move in slow motion. Does time resolution really increase during the event or is it all an illusion?

Chess Stetson, Matthew P. Fiesta and David M. Eagleman (2007) decided to test this hypothesis. Using a hand-held device to measure speed of visual perception, they made volunteers free fall for 31 m before landing safely in a net. This device displayed a series of digits in high speed, so that they couldn’t be read by the  by the participants. The idea was that if time really slows down while we experience a frightening event (free falling), the participants could successfully read some or all of the digits displayed on the device’s screen. In addition to that, after landing they were asked to make duration judgements about their fall and the fall of others.

Although the participants  free-falling from 50 meters experienced a duration expansion,  no evidence of increased temporal resolution was found. Contrary to the initial hypothesis, they failed to read the digits that were displayed on the hand-held device. The results of this study don’t support the hypothesis that subjective time as a whole runs in slow motion during frightening events. The researchers suggest that the slowing of time that’s reported is a function of our recollection and not perception:

“The involvement of the amygdala in emotional memory may lead to dilated
duration judgments retrospectively, due to a richer, and perhaps
secondary encoding of the memories. Upon later readout,
such highly salient events may be erroneously interpreted to have
spanned a greater period of time.”

You can read the original study here.

Further Reading:

Changing Time and Emotions – Pierre-Yves Geoffard & Stéphane Luchini (2007)
Time and the Brain: How Subjective Time Relates to Neural Time – David M. Eagleman, Peter U. Tse, Dean Buonomano, Peter Janssen, Anna Christina Nobre & Alex O. Holcombe (2005)

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