Some take the tube, others the train…The Amazing Race in the brain
It makes sense that we need to process and respond to some stuff we see quicker than other stuff we see. Take for instance a lion versus a lollipop. This paper by Pessoa and Adolphs explores the mechanisms behind emotional processing of visual stimuli, and more specifically provides us with compelling evidence for a new way of thinking about it.
Regarding the processing of affective visual stimuli, there is a standard hypothesis: A sub-cortical pathway (quicker than any cortical route) from the superior colliculus to the pulvinar nucleus of the thalamus to the amygdala plays a prominent role in the processing of affective visual stimuli – that is, stimuli that are emotionally meaningful . This has been regarded as a fast and efficient process for information with survival value (the nearby lion). The information in the pathway is processed automatically—that is, independently of attention and awareness .
But here is a different view: We shouldn’t be so quick to discount the cortex in visual information processing. It is not that much slower than sub-cortical processing. What’s important is the point we can reliably discern between affective and non-affective stimuli, rather than simply the timing of our initial response. And in light of some of the literature in visual task performance, the authors state that the processing of affective visual stimuli is no faster than processing of other visual stimuli.
The authors challenge the notion that processing of affective visual stimulus is carried out independently of awareness and attention. And they question whether the amygdala is essential for this . An emphasis is instead placed on the pulvinar nucleus. The what? The pulvinar. PULL. VIN. AAAAAAGH. Well, the pulvinar WAS considered just a relay station, but these guys suggest it is a key component of visual circuitry. Their proposal seems sensible – most pulvinar nuclei are involved in thalamo-cortical loops, connecting with numerous sites on the cortex, not just the colliculus. Finally, and most interestingly I think, the pulvinar may have a role in filtering out distractions and finding what is salient in a visual scene . Relay station! Ha!
A multiple-waves model is suggested; numerous alternatives (with an emphasis on cortical) to the colliculus—pulvinar—amygdala pathway make for fast, albeit coarse, visual processing of affective stimuli. And what parts do the pulvinar and the amygdala play in this model? Well most of the input to the pulvinar comes from the cortex. The pulvinar, together with its cortically connected sites, determines the behavioural relevance of a stimulus, then amplifies responses to those survival-significant stimuli (usually the lions as opposed to the lollipops). And the amygdala’s role is a modulatory one, much better reflected by its numerous cortical connections than its sub-cortical connections . It’s proposed that the amygdala has a role in prioritising information processing; in light of its broad connectivity it determines the allocation of ‘processing resources’ to stimuli that are biologically relevant.
So it seems that it comes down to ‘survival processing’ rather than emotion processing. The quickest way of relaying such information is not necessarily in the sub-cortex, and probably not confined to one typical pathway. And I can’t help thinking that if it’s all about self-preservation, it is possible that people in pain may in fact process body-related information differently to the rest of us – do they take the tube or the train?
Flavia Di Pietro is a PhD student in the Moseley Group investigating the development of Complex Regional Pain Syndrome (CRPS) after wrist fracture. Flavia’s PhD focuses on the early detection of brain changes in CRPS using fMRI. But get this – Flavia did Physiotherapy Honours degree at Notre Dame and completely cleaned up – Brian Edwards Memorial Award, Physio Research Foundation Award, Dean’s Award. Now, these things mean that she is not only ticking the academic boxes but all the other fluffy stuff too. No surprises that the NHMRC of Australia jumped to support her PhD. So she has come over from Perth where she has been working as a physiotherapist. All her achievements, however, pale in comparison to her celebrated status as the best Shoe Salesperson south of Milano, as evidenced by her taking out the 2006 and 2008 Diana Ferrari Golden Boot Award. Clearly, she did not write this bio.
* One of the awards in Flavia’s bio is fictitious.
 Morris, J. (1999). A subcortical pathway to the right amygdala mediating “unseen” fear Proc. Natl Acad. Sci. USA , 96 (4), 1680-1685 DOI: 10.1073/pnas.96.4.1680
 Pessoa, L. (2005). To what extent are emotional visual stimuli processed without attention and awareness? Current Opinion in Neurobiology, 15 (2), 188-196 DOI: 10.1016/j.conb.2005.03.002
 Tsuchiya N, Moradi F, Felsen C, Yamazaki M, & Adolphs R (2009). Intact rapid detection of fearful faces in the absence of the amygdala. Nature neuroscience, 12 (10), 1224-5 PMID: 19718036
 Ungerleider LG, & Christensen CA (1979). Pulvinar lesions in monkeys produce abnormal scanning of a complex visual array. Neuropsychologia, 17 (5), 493-501 PMID: 117393
 Vuilleumier P, Richardson MP, Armony JL, Driver J, & Dolan RJ (2004). Distant influences of amygdala lesion on visual cortical activation during emotional face processing. Nature neuroscience, 7 (11), 1271-8 PMID: 15494727