West, G.L., Anderson, A.K., Bedwell, J.S., & Pratt, J. (2010). Red diffuse light suppresses the accelerated perception of fear. Psychological Science, 21, 992-9.

Prioritization of affective events may occur via two parallel pathways originating from the retina-a parvocellular (P) pathway projecting to ventral-stream structures responsible for object recognition or a faster and phylogenetically older magnocellular (M) pathway projecting to dorsal-stream structures responsible for localization and action. It has previously been demonstrated that retinal exposure to red diffuse light suppresses M-cell neural activity. We tested whether the fast propagation along the dorsal-action pathway drives an accelerated conduction of fear-based content. Using a visual prior-entry procedure, we assessed accelerated stimulus perception while either suppressing the M pathway with red diffuse light or leaving it unaffected with green diffuse light. We show that the encoding of fearful faces is accelerated, but not when M-channel activity is suppressed, revealing a dissociation that implicates a privileged neural link between emotion and action that begins at the retina.

The flat earth and geocentric world are examples of wrong scientific beliefs that were held for long periods. Can you name your favorite example and for extra credit why it was believed to be true?

This made me think of perhaps a less famous example, but one that tends to irk me when I encounter it (which is often) – the idea that Rapid Eye Movement (REM) sleep is synonymous with dreaming. This idea has persisted (and in some cases, still persists) for decades, despite clear evidence that it is not true.

How did the idea that REM=dreaming originate? As most people will know, sleep consists of distinct fluctuating stages. REM sleep is a stage that occupies roughly 20% of the average person’s sleep cycle. It occurs in most mammals and birds (there is some controversy over whether it exists in reptiles and other cold-blooded animals). REM is different from the other sleep stages in that monitoring of multiple physiological systems during this phase indicates clear signs of arousal. In fact, brain electrical signatures during this stage appear very similar to what is observed during wakefulness (so much so, that REM has been called ‘paradoxical’ sleep). Likewise breathing becomes quicker and other forms of arousal are evident – both female and male genitals become engorged with blood. Muscle tone changes due to paralysis of large muscle groups – an important exception being the muscles that control eye movement. In fact, the eye muscles are very active during this stage (thus the name, Rapid Eye Movement).

Early on, scientists noted that if you wake people from REM sleep versus other Non-REM (NREM) stages, they are much more likely to report dreams (traditional research has suggested that the ratio of dreaming in REM:NREM is about 8:2). Given the fallibility of memory for dreams, researchers at this point more or less equated REM with dreaming and NREM with a lack of it. Since the REM state can be clearly monitored by measuring physiological arousal and since it is highly conserved in mammals, this opened the door for scientists to begin investigating the exact brain mechanisms that generate REM sleeping (and, by proxy, dreaming).

The work of many fine scientists (a large portion of it on sleeping cats) identified the pons as critical for the onset of REM sleep. The pons is a structure that is located in the lower brainstem.
Destroying the pons leads to a loss of REM sleep. Scientists also showed that fluctuations between REM and NREM sleep are mediated by oscillations in circulating neurotransmitters – REM sleep is dominated by acetylcholine bursts, while NREM is punctuated by serotonin and norepinephrine (reciprocal-interaction between these neurochemicals leads to the iterative cycles REM/NREM).

At this point, sleep scientists were ready formulate a theory of dreaming on the basis of knowledge about the neurobiology of REM sleep. This became known as the activation-synthesis theory – the idea that during REM sleep, volleys of activity from the pons activate the forebrain (the activation part of the theory). The resultant random activations of the forebrain then require integrating and making sense of these essentially meaningless signals (the synthesis part). However, at this point, no one really thought to check the hypothesis that REM=dreaming (obviously, the animal researchers couldn’t ask the cats to report on their dreams). It actually took several decades before clinical reports of humans who had sustained damage to their pons were used to check the theory – despite the absence of REM sleep in these patients, they regularly reported having dreams! Amazingly, another source of evidence that was crucial to this puzzle was around all along – however, it was restricted to the psychiatric community and was never transferred to neuroscientists. This was the observation that among patients who had had a frontal leucotomy – a severing of connections between their frontal brain and the so-called ‘limbic zones’ – dreaming was almost invariably eliminated. The evidence began to pile that the pons was not the primary generator of dreams (though it was the generator of REM sleep).

Taken together with more recent neuroimaging studies, we now know that there appear to be several brain regions that are critical to dreaming (that is, if they are damaged, dreaming will cease). One of these is a region in the posterior part of the cerebral cortex that has to do with integrating information from multiple sensory modalities (visual, auditory, somatosensory). The other key structure is the limbic frontal white matter (which is destroyed by a frontal leucotomy). Subsequent research also showed that reports of dreams in NREM stages are far more common – especially during sleep onset and close to awakening. In fact, depending on how questions are phrased to research participants, up to 70% of NREM awakenings can lead to report of some sort of substantive conscious mental activity.

It is now clear that the reason that REM is correlated (but not causal!) of dreams is that dreaming requires some form of brain arousal. Pons activation provides such a ‘fuel’ but it is not the sought-for dream state ‘generator’ per se. Other forms of forebrain arousal that can lead to dreams in NREM states include hormonal surges as well as the residues of waking mental activity (the latter is especially the case for those dreams in the initial sleep onset stage).

However, in spite of conclusive evidence that REM can be disassociated from dreaming, the REM=dreaming hypothesis is remarkably prevalent – not only in popular science media but also in many academic textbooks!

“For any action we perform, we cannot justifiably claim to know, from the first-person perspective,whether our prior choices are among the actual causes of our action.”

He goes on to conclude that “…that we humans are unwitting hostages to those things that rise to conscious awareness, that we unwittingly
fail to credit much that does not come to conscious awareness, and that we are particularly oblivious to the effects that our ancestral
affective capacities exert upon our less-ancestral and less-affective capacities as practical agents.”

See link here. Self-organization is at it again.

This is a myth that, in my own experience, is held by almost no one who is actually a neuroscientist. Indeed, to hold up consciousness as the apex of neural evolution and function does a real disservice to all of the complex processes carried out by the brain (and the body) which keep us alive and working well from day to day. And yes these same blind processes do the lion’s share of the work when it comes to many of those phenomena that some would subsume under the general label ‘mind’. There are innumerable interesting scientific questions and programs in all areas of neuroscience that have nothing to do with consciousness. The origin of this myth may derive in part from the (mistaken) belief that all causally important streams of processing have to be funneled through consciousness. The first real challenge to this philosophical stance came from Freud’s psychoanalysis. The final nail in the coffin has come from cognitive neuroscience. If anything, consciousness is highly overrated.

Consciousness uniquely defines us, as humans

This myth is steadily eroding, at least among neuroscientists, but it still has more traction than it deserves or is justified by empiricism. [A corollary of this myth involves the idea that consciousness is somehow dependent on language]. Almost all scientists working on consciousness make a distinction between different grades/forms of the process – in its broadest sense, this ranges from ‘primary’ or core to ‘secondary’ or extended consciousness. The belief that consciousness is somehow unique to humans is really just confused thinking having to do with using the term in too restrictive of a fashion. Sure, ‘autobiographical selves’ are elaborated to a greater extent in humans, with our expanded frontal lobes, but this is really only icing on the cake of consciousness, so to speak – in a way, it is similar to how wine connoisseurs have a more recognizing palate than the rest of us. However, one should not be surprised that ‘primary’ consciousness is a more ancient property of neural tissue, that is probably (at the very least) present in all mammals. This conclusion follows quite naturally from a consideration of our evolutionary heritage. Interested readers are encouraged to read more about the work of Jaak Panksepp [Panksepp, J. (2005) Affective consciousness: Core emotional feelings in animals and humans. Consciousness and Cognition, 14, 30-80] and Derek Denton [Denton, D.A. et al. (2009). The role of primordial emotions in the evolutionary origin of consciousness. Consciousness and Cognition, 18, 500-514].

A scientific theory of consciousness should somehow simulate consciousness

This is a common point that seems implicit especially among philosophers who like to talk consciousness – some version of this argument is often told as the story of ‘Mary the Blind Neuroscientist’. If the ‘problem’ of consciousness is set up as: “Okay, you’ve told us about the properties of neural networks that are necessary for consciousness, but this still doesn’t EXPLAIN it!” then it’s creating an argument that can in principle never be closed. If you expect a scientific theory of consciousness to simulate the experience (the ‘qualia’) of being a conscious entity, then you may as well save your self a lot of effort and energy – it won’t happen…ever. This is a philosophical problem, not a scientific one.

Quantum physics is necessary for a scientific understanding of consciousness

Consciousness is fundamentally a biological property – and it is to be addressed through the methods of biology and neurophysiology. Quantum physics is as much necessary for a scientific understand of consciousness as it is for understanding how your alarm clock works. This sort of reminds me of when people taught that the methods of physics would be necessary to crack the DNA code – again, a scientific problem that was ultimately solved using biological tools and methods. Recommended reading – [Segalowitz, S.J. (2009). A quantum physics account for consciousness: Much less than meets the eye. Brain and Cognition, 71, 53.].

Consciousness is a ‘thing’

Consciousness is somehow the special property of a particular kind of neuron (or microtubule) or some special, perhaps as yet undiscovered brain region. Not sure if anyone really still believes in these sorts of arguments. Consciousness is undoubtedly a neurodynamic process, NOT a thing – what neuroanatomy does is to constrain and guide scientific theories of consciousness (e.g., we can look at the anatomy of cerebellar circuits and think about why their architecture is not well suited to support conscious processes – namely, it has to do with the lack of reentrant pathways] but it doesn’t hold the answer.