Specific Brain Areas for Sex, Money

This image illustrates the dissociation between primary and secondary rewards in the orbitofrontal cortex, a frontal region of the brain that is known to play a role in the evaluation of gratification. The more primitive region (in the back, shown in yellow) represents the value of erotic images shown to the participants, while the most recent region (in the front, in blue) represents the value of monetary prizes won by the volunteers in the experiment. Credit: © Sescousse / Dreher

A team of French researchers headed by Jean-Claude Dreher of the Centre de Neuroscience Cognitive in Lyon, France, has provided the first evidence that the orbitofrontal cortex (located in the anterior ventral part of the brain) contains distinct regions that respond to secondary rewards like money as well as more primary gratifications like erotic images. These findings, published in The Journal of Neuroscience, open new perspectives in the understanding of certain pathologies, such as gambling addiction, and the study of the neural networks involved in motivation and learning.

In our everyday lives, we often encounter various types of "rewards": a 20-euro bill, a chocolate bar, a glass of good wine... Moreover, we must often choose between them, or trade one for another. To do this, we must be able to compare their relative value on a single consistent scale, which suggests that all types of rewards are assessed in the same brain areas. At the same time it is possible that, due to their individual characteristics, different rewards may activate distinct cerebral regions. In particular, there could be a dissociation between so-called "primary" gratifications such as food or sex, which satisfy basic vital needs and have an innate value, and more "secondary" rewards such as money or power, which are not essential for survival and whose value is assessed by association with primary gratifications.

To verify these hypotheses, Jean-Claude Dreher and Guillaume Sescousse conducted an original experiment in the form of a game that rewarded 18 volunteers with money or erotic images, while their cerebral activity was monitored using an FMRI (functional magnetic resonance imaging) scanner.

The experiment showed that the rewards are indeed evaluated in partially shared cerebral regions, namely the ventral striatum, insula, mesencephalon and anterior cingulate cortex. The researchers have also confirmed that there is a dissociation between primary and secondary rewards in the orbitofrontal cortex. Its posterior region (more primitive) is specifically stimulated by erotic images (a primary reward), while its anterior region (which is more recent in man) is activated by monetary gain (a secondary reward). The more abstract and complex the reward, the more its representation stimulates the anterior regions of the orbitofrontal cortex.

The volunteers in the experiment played a game in which they could win money or view erotic images, while their cerebral activity was recorded using an FMRI scanner. Credit: © CERMEP - Imagerie du Vivant

These results provide the first evidence of a dissociation in the brain between two types of reward, suggesting the existence of distinct regions corresponding to various gratifications. Dreher and Sescousse's research could lead to a better understanding of certain psychiatric disorders, including gambling addiction.

More information: G. Sescousse, J. Redouté, J-C Dreher (2010) The architecture of reward value coding in the orbitofrontal cortex. J Neurosci, 30 (39)

Provided by CNRS

Journal Reference:

G. Sescousse, J. Redoute, J.-C. Dreher. The Architecture of Reward Value Coding in the Human Orbitofrontal Cortex. Journal of Neuroscience, 2010; 30 (39): 13095 DOI: 10.1523/JNEUROSCI.3501-10.2010

The Neural Basis of Synesthesia

Wikipedia has a page on the neural basis of synesthesia, but not yet described there is a new study in press by Vilayanur S. Ramachandran’s group that provides interesting insights.

Synesthesia is a neurological condition in which affected individuals experience one sense (e.g. hearing) as another sense (e.g. visual colours). Ramachandran’s latest study investigated grapheme-colour synesthetes who experience specific colours when they view specific graphemes (i.e., letters and numbers). The results demonstrate that two brain areas – for grapheme and colour representation respectively – are activated at virtually the same time in the brains of synesthetes who are viewing letters and numbers. On the other hand, normal controls viewing the same thing exhibit activity in the grapheme region but not the colour region.

This is the first study of synesthesia to demonstrate simultaneous activation of the two brain areas, known as the posterior temporal grapheme area (PTGA) and colour area V4 (pictured below in the brain of a representative synesthete). The finding was made possible because the researchers used a neuroimaging technique called magnetoencephalography (MEG) to measure weak magnetic fields emitted by specific areas of the brain while the subjects viewed graphemes. Compared to other neuroimaging techniques, such as fMRI and EEG, MEG offers the best combination of temporal and spatial precision in measuring brain activation.

If you read the Wikipedia page, you know that there are two main theories that attempt to explain how synesthesia occurs in the brain: the cross-activation theory and the disinhibited feedback theory. Let’s call them Theory 1 and Theory 2 for simplicity. Theory 1 posits that the grapheme and colour brain areas are ‘hyper-connected’ such that activity in the grapheme area evoked by viewing a letter or number immediately leads to activity in the colour area and conscious perception of colour. Theory 2 maintains that there are ‘executive’ brain areas that control the communication between the grapheme and  colour areas, and in synesthetes this control is disrupted. To reiterate, Theory 1 says that normal brains are anatomically different than synesthete brains, whereas Theory 2 says that normal brains are the same as synesthete brains but the two brains act differently.

The results of Ramachandran’s group support Theory 1, the cross-activation theory, since this model predicts that the colour and grapheme areas should be activated at roughly the same time in synesthetes looking at graphemes.

This is perhaps the strongest evidence for the cross-activation theory of synesthesia to date. But to complicate things, Ramachandran’s group proposed a new theory called ‘cascaded cross-tuning model,’ which is essentially a refinement of the cross-activation model (let’s call it Theory 1.1).

According to Theory 1.1, when a synesthete views a number, a series of simultaneous activations lead to perception of a colour. First, a subcomponent of the grapheme area responds to features of the number (e.g. the “o” that makes up the top of the number 9). This leads to activity in other subcomponents of the grapheme area representing possible numbers that the feature is part of (e.g. the “o” could be a component of the numbers 6, 8, or 9) as well as the colour area V4. At this point however, colour is not consciously perceived. Next, when the grapheme area identifies the number 6 (based on monitoring by other brain areas), activity in V4 is triggered, leading to conscious perception of the colour associated with the number 6.

Cool theory? Cool theory.

Note, however, that it only applies to ‘projector’ synesthetes who see colours in the outside world when they see numbers, but not ‘associator’ synesthetes who perceive the colours in the “mind’s eye.” Also, it doesn’t yet apply to other forms of synesthesia, such as acquired synesthesias (e.g. synesthesia for pain).

Yeah, it’s only a matter of time before Theory 1.2 takes over.

Reference:
Brang D, Hubbard EM, Coulson S, Huang M, & Ramachandran VS (2010). Magnetoencephalography reveals early activation of V4 in grapheme-color synesthesia. NeuroImage PMID: 20547226

An Old Illusion

The Monkey Business Illusion

 

"Imagine you are asked to watch a short video (above) in which six people-three in white shirts and three in black shirts-pass basketballs around. While you watch, you must keep a silent count of the number of passes made by the people in white shirts. At some point, a gorilla strolls into the middle of the action, faces the camera and thumps its chest, and then leaves, spending nine seconds on screen. Would you see the gorilla?

Almost everyone has the intuition that the answer is "yes, of course I would." How could something so obvious go completely unnoticed? But when we did this experiment at Harvard University several years ago, we found that half of the people who watched the video and counted the passes missed the gorilla. It was as though the gorilla was invisible.

This experiment reveals two things: that we are missing a lot of what goes on around us, and that we have no idea that we are missing so much. To our surprise, it has become one of the best-known experiments in psychology. It is described in most introductory textbooks and is featured in more than a dozen science museums. It has been used by everyone from preachers and teachers to corporate trainers and terrorist hunters, not to mention characters on the TV show C.S.I., to help explain what we see and what we don't see. And it got us thinking that many other intuitive beliefs that we have about our own minds might be just as wrong. We wrote The Invisible Gorilla to explore the limits of human intuition and what they mean for ourselves and our world. We hope you read it, and if you do, we would love to hear what you think."

-Christopher Chabris and Daniel Simons 

www.theinvisiblegorilla.com