Posts Tagged ‘fMRI’

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

Distractibility is Reflected in the Structure and Function of the Parietal Cortex

08/05/2011 6 comments

Sustaining attention and blocking goal-irrelevant information is a crucial function in everyday life. Kanai and colleagues combining neuroimaging, self-report judgements and TMS found evidence that indicates that a region of the left superior parietal cortex mediates this function.

The ability to avoid distractibility varies across individuals as measured by the Cognitive Failures Questionnaire (CFQ) (Broadbent et al., 1982). Studies on twins and families have showed that the ability to maintain attention in the presence of distractors is highly heritable (Boomsma, 1998). High degree of heritability suggests that the variability might be mediated by genetic influences on the brain, which may be expressed via variability in brain structure.

This hypothesis was tested by Kanai et al. by scanning 145 healthy adult individuals and obtaining their CFQ scores. They used voxel-based morphometry (VBM) to examine whether distractibility scores predicted brain structure. Their results revealed that the level of an individual’s distractibility in everyday life was predicted by variability in regional grey matter density of the left superior parietal lobe (SPL). Highly distractable individuals had larger grey matter density at the left SPL. This particular region has been implicated in top-down attentional control in previous studies (Mevorach et al., 2009). To examine whether there is a causal relationship between this region and distractibility, Kanai et al. applied transcranial magnetic stimulation (TMS) over the left SPL of the participants while they were performing an attentional capture paradigm. The results of the experiment suggest that the left SPL plays a role in suppressing distraction from task-irrelevant salient distractors in both visual fields.

ResearchBlogging.orgKanai R, Dong MY, Bahrami B, & Rees G (2011). Distractibility in daily life is reflected in the structure and function of human parietal cortex. The Journal of neuroscience : the official journal of the Society for Neuroscience, 31 (18), 6620-6 PMID: 21543590

Boomsma, D. I. (1998). Genetic analysis of cognitive failures (CFQ): a study of dutch adolescent twins and their parents. Eur. J. Pers., 12(5):321-330.

Broadbent, D. E., Cooper, P. F., FitzGerald, P., and Parkes, K. R. (1982). The cognitive failures questionnaire (CFQ) and its correlates. The British journal of clinical psychology / the British Psychological Society, 21 (Pt 1):1-16.

Mevorach, C., Shalev, L., Allen, H. A., and Humphreys, G. W. (2009). The left intraparietal sulcus modulates the selection of low salient stimuli. Journal of cognitive neuroscience, 21(2):303-315.

Your brain on improv

08/01/2011 3 comments

Charles Limb is a surgeon and musician who is investigating the neural correlates of musical creativity. You might remember his very cool fMRI study of jazz improvisation. You can read it here. He talks about this and other projects he’s working on in his recent TED talk. We need more studies like these!

Future Imagining And Episodic Memory

27/08/2010 2 comments

Neuroimaging and lesion studies suggest that imagining the future (i.e. envision future personal experiences) is strongly connected with retrospective memory (i.e. remembering past experiences). Two recent papers published on Neuropsychologia investigated the relationship of retrospective memory and future imagining, as well as their common neural correlates.

Kwan, Carson, Addis, and Rosenbaum (2010) report the case of H.C., a young woman with developmental amnesia associated with bilateral hippocampal loss. Episodic memory seems to depend on hippocampal function (Yancey & Phelps, 2001; Maguire, 2001). Compared to matched controls H.C. was found to be impaired both in tasks requiring past and future event generation. Her performance was similarly deficient in both tasks. According to Kwan and colleagues:

These results indicate that mental time travel can be compromised in hippocampal amnesia, whether acquired in early or later life, possibly as a result of a deficit in reassembling and binding together details of stored information from earlier episodes

Maguire, Vargha-Khadem, and Hassabis (2010) report the cases of two patients (P01 and Jon) with dense amnesia and 50% volume loss in both hippocampi. P01 suffered from adult-acquired amnesia, but unlike previously reported cases was found to be unimpaired at future imagining tasks. The authors suggested that P01 could have been an atypical case, and in order to investigate this they identified another patient with similar neuropsychological profile, Jon. In spite of his dense amnesia, Jon was able to imagine future experiences in a comparable manner to control participants. According to one of the possible explanations proposed by Maguire and colleagues:

Activity in their residual hippocampal tissue supports the ability to imagine new scenarios, and that this is the key feature. Residual hippocampal tissue was active in both patients and in similar circumstances to control participants. Whilst we cannot definitely relate function to these hippocampal activations, we suggest the activations might indicate some preserved hippocampal function which is also sufficient to support their preserved ability to imagine scenarios

ResearchBlogging.orgKwan, D., Carson, N., Addis, D., & Rosenbaum, R. (2010). Deficits in past remembering extend to future imagining in a case of developmental amnesia Neuropsychologia, 48 (11), 3179-3186 DOI: 10.1016/j.neuropsychologia.2010.06.011

Maguire, E., Vargha-Khadem, F., & Hassabis, D. (2010). Imagining fictitious and future experiences: Evidence from developmental amnesia Neuropsychologia, 48 (11), 3187-3192 DOI: 10.1016/j.neuropsychologia.2010.06.037

Decoding Mental States

Internet is a wonderful place.. During a google search, I came across these very interesting videos on information-based analysis and decoding mental states and processes:

Decoding mental states from human brain activity

John-Dylan Haynes

Overview of decoding of mental states and processes

Tom Mitchell

Exploring human object-vision with hi-res fMRI and information-based analysis

Nikolaus Kriegeskorte

fMRI Limitations And Criticism

10/11/2009 1 comment

FMRI-scan_sectie_85Fancy images, impressive results, but can we really trust the reports of the majority of the neuroimaging studies out there? Here’s a couple of papers discussing the limitations of fMRI that you can read, if you’re interested in learning more about this method:

1. a great review by Nikos K. Logothetis published in Nature a year ago. Here’s the abstract:

Here I give an overview of the current state of fMRI, and draw on neuroimaging and physiological data to present the current understanding of the haemodynamic signals and the constraints they impose on neuroimaging data interpretation. Functional magnetic resonance imaging (fMRI) is currently the mainstay of neuroimaging in cognitive neuroscience.
Advances in scanner technology, image acquisition protocols, experimental design, and analysis methods promise to push forward fMRI from mere cartography to the true study of brain organization. However, fundamental questions concerning the interpretation of fMRI data abound, as the conclusions drawn often ignore the actual limitations of the methodology.”

2. Professor D. Attwell questions the neural basis of functional brain imaging signals:

“The haemodynamic responses to neural activity that underlie the blood-oxygen-level-dependent (BOLD) signal used in functional magnetic resonance imaging (fMRI) of the brain are often assumed to be driven by energy use, particularly in presynaptic terminals or glia.However, recent work has suggested that most brain energy is used to power postsynaptic currents and action potentials rather than presynaptic or glial activity and, furthermore, that haemodynamic responses are driven by neurotransmitter-related signalling and not directly by the local energy needs of the brain. A firm understanding of the BOLD response will require investigation to be focussed on the neural signalling mechanisms controlling blood flow rather than on the locus of energy use.”

P.S: For an introduction to fMRI, visit fMRI 4 Newbies website.

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