Prospection: simulation of future unique to humans

Gilbert and Wilson offer a concise review of our unique human ability to simulate the future, covering brain regions involved and stereotyped errors that occur (PDF here). (I did a series of posts in June, 2006 abstracting Gilberts book "Stumbling on Happiness." You can use the blog search box to find them by entering the word "stumbling.") Here are some clips:

Prefeelings will be reliable predictors of subsequent hedonic experiences when two conditions are met. As the figure shows, when we are in the present (T₁) attempting to predict our hedonic reaction to an event in the future (H₂), our present hedonic experience (H₁) is influenced by our simulation of the future event (e₁) as well as by contextual factors (₁), such as the events that are occurring in the present, the thoughts we are having in the present, our present bodily states, and so on. We feel better when we imagine going to the theater than to the dentist, but we feel better imagining either event on a sunny day than on a rainy day, or when we are well rather than ill. Similarly, our future hedonic experience (H₂) will be influenced both by our perception of the event (e₂) and by contextual factors (₂). Because our hedonic experiences are influenced both by our mental representation of the event and by contextual factors, our present hedonic experience will be a reliable predictor of our future hedonic experience if and only if (i) our simulation of the event at T₁ exerts the same influence on our hedonic experience at T₁ as our perception of the event at T₂ exerts on our hedonic experience at T₂, and (ii) contextual factors at T₁ exert the same influence on our hedonic experience at T₁ as contextual factors at T₂ exert on our hedonic experience at T₂. In other words, H₁ = H₂ if and only if e₁ = e₂ and ₁ = ₂. Errors in prospection arise from the fact that people use their prefeelings to make hedonic predictions even when one or both of these conditions is not met. These errors are of four kinds.

Simulations are unrepresentative. We naturally imagine our next dental appointment by remembering our last one.... research suggests that people often use unrepresentative memories as a basis for simulation. For example, when people who have missed trains in the past are asked to imagine missing a train in the future, they tend to remember their worst train-missing experience rather than their typical train-missing experience.

Simulations are essentialized. When we imagine "going to the theater next week," we don't imagine every detail of the event, but rather, we imagine the essential features that define it. We imagine seeing a stage filled with actors but we do not imagine parking the car, checking our coat, or finding our seat. The problem with omitting inessential features from simulations is that such features can profoundly influence our subsequent hedonic experience... Because simulations omit inessential features, people tend to predict that good events will be better and bad events will be worse than they actually turn out to be. The young couple who simulate the joys of parenthood but fail to simulate the drudgery of diapers are unlikely to have the hedonic experience they imagined.

Simulations are abbreviated. If we imagined each and every moment of the events we were simulating, our simulations would take as long as the events themselves. Simulations are naturally abbreviated and represent just a few, select moments of a future event. The moments they select tend to be the early ones. When people imagine what their lives would be like if they won the lottery or became paraplegic, they are more likely to imagine the first day than the two-hundred-and-ninety-seventh. The problem with imagining only the early moments of an event is that hedonic reactions to events typically dissipate over time, which means that mental simulations tend to the moments that evoke the most intense pleasure or pain.

Simulations are decontextualized. Research shows that people often do not consider the potentially significant differences between contextual factors at T1 and T2 when using their present hedonic state to predict their future hedonic state. For example, hungry people mistakenly expect to like eating spaghetti for breakfast the next day, and sated people mistakenly expect to dislike eating it for dinner the next day. People who have just exercised mistakenly expect to enjoy drinking water the next day more than do people who are about to exercise (53). In both cases, people do not seem to realize that their present hunger and thirst are influencing their hedonic reactions to simulated future consumption. They ignore the fact that the contextual factors that are presently exerting an influence at T1 (i.e., hunger and thirst) will not exert the same influence at T2.

Their conclusion makes a nice summary of how modern and ancient brain systems interact in imagining possible future feelings:

Mental simulation is the means by which the brain discovers what it already knows. When faced with decisions about future events, the cortex generates simulations, briefly tricking subcortical systems into believing that those events are unfolding in the present and then taking note of the feelings these systems produce. The cortex is interested in feelings because they encode the wisdom that our species has acquired over millennia about the adaptive significance of the events we are perceiving. Alas, actually perceiving a bear is a potentially expensive way to learn about its adaptive significance, and thus evolution has provided us with a method for getting this information in advance of the encounter. When we preview the future and prefeel its consequences, we are soliciting advice from our ancestors.

This method is ingenious but imperfect. The cortex attempts to trick the rest of the brain by impersonating a sensory system. It simulates future events to find out what subcortical structures know, but try as it might, the cortex cannot generate simulations that have all the richness and reality of genuine perceptions. Its simulations are deficient because they are based on a small number of memories, they omit large numbers of features, they do not sustain themselves over time, and they lack context. Compared to sensory perceptions, mental simulations are mere cardboard cut-outs of reality. They are convincing enough to elicit brief hedonic reactions from subcortical systems, but because they differ from perceptions in such fundamental ways, the reactions they elicit may differ as well. Although prospection allows us to navigate time in a way that no other animal can, we still see more than we foresaw.

Evolving size of the social brain.

Dunbar and Shultz ask why primates have such large brains, compared to their body mass, compared with other animals. Here is their abstract, followed by a central clip from their article:

The evolution of unusually large brains in some groups of animals, notably primates, has long been a puzzle. Although early explanations tended to emphasize the brain's role in sensory or technical competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains. However, recent analyses suggest that it may have been the particular demands of the more intense forms of pairbonding that was the critical factor that triggered this evolutionary development. This may explain why primate sociality seems to be so different from that found in most other birds and mammals: Primate sociality is based on bonded relationships of a kind that are found only in pairbonds in other taxa.

Figure - In anthropoid primates, mean social group size increases with relative neocortex volume (indexed as the ratio of neocortex volume to the volume of the rest of the brain). Solid circles, monkeys; open circles, apes. Regression lines are reduced major axis fits.


The important issue in the present context is the marked contrast between anthropoid primates and all other mammalian and avian taxa (including, incidentally, prosimian primates): Only anthropoid primates exhibit a correlation between social group size and relative brain (or neocortex) size. This quantitative relationship is extremely robust; no matter how we analyze the data (with or without phylogenetic correction, using raw volumes, or residuals or ratios against any number of alternative body or brain baselines) or which brain data set we use (histological or magnetic resonance imaging derived, for whole brain, neocortex, or just the frontal lobes), the same quantitative relationship always emerges. This suggests that, at some early point in their evolutionary history, anthropoid primates used the kinds of cognitive skills used for pairbonded relationships by vertebrates to create relationships between individuals who are not reproductive partners. In other words, in primates, individuals of the same sex as well as members of the opposite sex could form just as intense and focused a relationship as do reproductive mates in nonprimates. Given that the number of possible relationships is limited only by the number of animals in the group, primates naturally exhibit a positive correlation between group size and brain size. This would explain why, as primatologists have argued for decades, the nature of primate sociality seems to be qualitatively different from that found in most other mammals and birds. The reason is that the everyday relationships of anthropoid primates involve a form of "bondedness" that is only found elsewhere in reproductive pairbonds.

MindBlog's home this morning...

The 1860 stone schoolhouse with its satellite dishes.

Nonhuman primates perceive human goals

Hauser and collaborators do a clever experiment to demonstrate that several primates can make inferences about a human experimenters goal that cannot be explained by simple associative learning. This means that our capacity to infer rational, goal-directed action derives from capabilities present in monkeys ~40 million years ago. Here is their abstract and a figure showing the basic idea of the experiment.

Humans are capable of making inferences about other individuals' intentions and goals by evaluating their actions in relation to the constraints imposed by the environment. This capacity enables humans to go beyond the surface appearance of behavior to draw inferences about an individual's mental states. Presently unclear is whether this capacity is uniquely human or is shared with other animals. We show that cotton-top tamarins, rhesus macaques, and chimpanzees all make spontaneous inferences about a human experimenter's goal by attending to the environmental constraints that guide rational action. These findings rule out simple associative accounts of action perception and show that our capacity to infer rational, goal-directed action likely arose at least as far back as the New World monkeys, some 40 million years ago.


Figure: During each trial, an experimenter presented subjects with two potential food containers, performed an action on one, and then allowed the subject to select one of the containers. In the intentional condition, the experimenter reached directly for and grasped the container. In the accidental condition, the experimenter flopped his hand onto the container with palm facing upwards in a manner that appeared, from a human perspective, accidental and non–goal-directed (13). If non-human primates fail to distinguish between intentional and accidental actions when making inferences about others' goals, attending to the mere association of the hand and container, then they should show the same pattern of searching in both conditions—that is, approach the experimenter-contacted container. However, if they distinguish between intentional and accidental actions, then they should selectively inspect the container targeted by the experimenter'sintentional action but not that targeted by accidental action.

A "language gene" in echolocating bats

Slightly altered abstract from Li et al.:

FOXP2 is a transcription factor implicated in the development and neural control of orofacial coordination, particularly with respect to vocalisation. [Thus, it is not really a "language gene" as indicated in many popular press reports.] Observations that orthologues show almost no variation across vertebrates yet differ by two amino acids between humans and chimpanzees have led to speculation that recent evolutionary changes might relate to the emergence of language. Echolocating bats face especially challenging sensorimotor demands, using vocal signals for orientation and often for prey capture. To determine whether mutations in the FoxP2 gene could be associated with echolocation, we sequenced FoxP2 from echolocating and non-echolocating bats as well as a range of other mammal species. We found that contrary to previous reports, FoxP2 is not highly conserved across all nonhuman mammals but is extremely diverse in echolocating bats. We detected divergent selection (a change in selective pressure) at FoxP2 between bats with contrasting sonar systems, suggesting the intriguing possibility of a role for FoxP2 in the evolution and development of echolocation. We speculate that observed accelerated evolution of FoxP2 in bats supports a previously proposed function in sensorimotor coordination.

Naturopathy wins over physical therapy advice?

Chronic lower back pain is perhaps the most commonly reported workplace disability. Szczurko et al. conducted a randomized clinical trial of 75 postal service employees experiencing more than six weeks of chronic back pain, dividing them to receive Naturopathic care (n = 39) or standardized physiotherapy (n = 36) over a period of 12 weeks. The study was conducted in clinics on-site in postal outlets. Participants in the Naturopathic care group received dietary counseling, deep breathing relaxation techniques and acupuncture. The control intervention received education and instruction on physiotherapy exercises using an approved education booklet. The authors suggest that naturopathic care provided statistically significant greater improvement than physiotherapy advice.

The naturopathic route involved hands-on intervention (acupuncture), and there is this curious point suggesting some rather significant motivational differences:

Data was available on 100% (39) of the naturopathic care group at week 8 and 75% (27) of the control group at week 8. Complete data on participants at week 12 was available on 92% and 63% respectfully.

Social cognitive skills unique to humans...

From Tomasello's group in Leipzig comes an article (PDF here), arguing for a distinctively human social cognitive intelligence rather a more "general intelligence" as distinguishing humans from the great apes. Here is their abstract:

Humans have many cognitive skills not possessed by their nearest primate relatives. The cultural intelligence hypothesis argues that this is mainly due to a species-specific set of social-cognitive skills, emerging early in ontogeny, for participating and exchanging knowledge in cultural groups. We tested this hypothesis by giving a comprehensive battery of cognitive tests to large numbers of two of humans' closest primate relatives, chimpanzees and orangutans, as well as to 2.5-year-old human children before literacy and schooling. Supporting the cultural intelligence hypothesis and contradicting the hypothesis that humans simply have more "general intelligence," we found that the children and chimpanzees had very similar cognitive skills for dealing with the physical world but that the children had more sophisticated cognitive skills than either of the ape species for dealing with the social world.

The decline of memory

J.L. Bader notes that Britney Spear's memory lapse while she was lip-synching during the recent MTV music video awards is a reflection of the general decline of dependence on memory in our culture. Why remember anything, when you can always google or wikipedia it; and all your contacts and phone numbers are stored in your cell phone? (And yes, I was one of the $200 beta testers of the Apple iPhone.) Some clips:

Oration and recitation, once staples of the American school system, have largely been phased out. Rhetoric programs at universities have narrowed, merged with communications departments, or been eliminated altogether...“We don’t have that kind of oral culture anymore,” said Prof. James Engell, author of “The Committed Word: Literature and Public Values,” who teaches a rhetoric course at Harvard. “We are in a culture that devalues our sense of memory.” Back when John Quincy Adams was teaching it, Mr. Engell said, “rhetoric was an umbrella where you got moral philosophy, the development of literary taste, intellectual prose, aesthetic appreciation, memorization and oral presentation. The ultimate object of this was what the Greeks called phronesis, or practical wisdom.”

...But contemporary scientists have discovered that memorization exercises can stave off dementia, introducing a new world of “neurobics.” Memory needs a workout as much as the abs do. Researchers have even shown that reciting poetry in dactylic hexameter can help synchronize heartbeats with breathing.

Lucid Dreaming makes the Styles section...

My, my, my..... how rapidly esoteric mind things become trendy. The lead article of the Sunday Styles section of the Sept 16 NY Times featured lucid dreaming. I've been to several consciousness meeting in which whole sessions were devoted to this capability. Actually it is not that esoteric...you probably have had experiences of being aware you were dreaming, of watching the action as a observer. The capability can be trained, and one can sometimes direct the action (even to the extent of indulging in some sexual fantasies that may not exactly be playing out in real life). I have played with this capability in my own dreaming, and find it to be much easier and cheaper than getting into computer facilitated alternative realities such as Second Life (I tried that too, felt like a dunce, and can't imagine how anyone finds the time.....).

Did Alex really "want" a cracker?

New York Times science writer George Johnson, who is one very intelligent guy, has done a nice piece on the capabilities and history of Alex the parrot (PDF here). I was unaware of several of the behaviors that had been noted in Alex:

“Want a nut!” Alex demanded. The interview was over. “Want a nut!” he repeated. “Nnn ... uh ... tuh.”...Dr. Pepperberg was flabbergasted. “Not only could you imagine him thinking, ‘Hey, stupid, do I have to spell it for you?’ ” she said. “This was in a sense his way of saying to us, ‘I know where you’re headed! Let’s get on with it.’ ”....She is quick to concede the impossibility of proving that the bird was actually verbalizing its internal deliberations. Only Alex knew for sure.

Next to infinity, one of the hardest concepts to grasp is zero. Toward the end of his life Alex may have been coming close. In a carnival shell game, an experimenter would put a nut under one of three cups and then shuffle them around. Alex would pick up the cup where the prize was supposed to be. If it wasn’t there he’d go a little berserk — a small step, maybe, toward understanding nothingness.

A bigger leap came in an experiment about numbers, in which the parrot was shown groups of two, three and six objects. The objects within each set were colored identically, and Alex was asked, “What color three?”.... “Five,” he replied perversely (he was having a bad attitude day), repeating the answer until the experimenter finally asked, “O.K., Alex, tell me, ‘What color five?’ ”....“None,” the parrot said....Bingo. There was no group of five on the tray. It was another of those high huneker moments. Alex had learned the word “none” years before in a different context. Now he seemed to be using it more abstractly....Dr. Pepperberg reported the result with appropriate understatement: “That zero was represented in some way by a parrot, with a walnut-sized brain whose ancestral evolutionary history with humans likely dates from the dinosaurs, is striking.”

This week's music - Debussy, Minuette from Suite Bergmanesque

Recorded Sept. 13 on my Steinway B at Twin Valley.

Let the kids decide.....

Placebo effect on human opiod pain system

A recent issue of Nature Reviews Neuroscience points to an interesting article by Wagner et al.
(open access).

The mere expectancy of pain relief has been shown to reduce pain in a manner that is reversible by opioid antagonists. Using positron-emission tomography and a mu-opioid-receptor selective radiotracer, Wagner et al. were able to measure the placebo-induced activation of the opioid system in specific brain regions. They found an increase in opioid neurotransmission in regions that have a central role in pain processing, demonstrating that placebo analgesic treatments potentiate the endogenous opioid response to painful stimuli.

Figure - Connectivity analysis of opioid binding potential. (A) 3D rendering of connectivity among regions that show placebo opioid responses.

The five "most popular" consciousness papers for August 2007

I pass on the report from the ASSC (Assoc. for Sci. Study of Cons.) of the papers most downloaded from their eprint archives in August:

1. Mashour, George A. (2007) Inverse Zombies, Anesthesia Awareness, and the
Hard Problem of Unconsciousness. In: 11th Annual Meeting of the ASSC, Las
Vegas.
(936 downloads from 21 countries). http://eprints.assc.caltech.edu/294/
2. Windt, Jennifer Michelle and Metzinger, Thomas (2006) The philosophy of
dreaming and self-consciousness: What happens to the experiential subject
during the dream state? In: The new science of dreaming (928 downloads from
19 countries). http://eprints.assc.caltech.edu/200/
3. Koriat, A. (2006) Metacognition and Consciousness. In: Cambridge handbook
of consciousness. CUP (801 downloads from 18 countries)
http://eprints.assc.caltech.edu/175/
4. Rosenthal, David (2007) Consciousness and its function. In: 11th annual
meeting of the Association for the Scientific Study of Consciousness, 22-25
June 2007, Las Vegas, USA. (741 downloads from 19 countries).
http://eprints.assc.caltech.edu/293/
5. Rosen, Alan and Rosen, David B. (2006) The Design of a
Sensation-generating Mechanism in the Brain: A first step towards a
quantitative definition of consciousness. Consciousness and Cognition,
CONCOG-06-00174 (596 downloads from 18 countries).
http://eprints.assc.caltech.edu/195/

Mind Over Manual

This is the title of an Op-Ed piece in the 9/13/2007 NY Times by Sally Satel which describes the difficulties and issues faced by the forthcoming revision (due in 2012) of the Diagnostic and Statistical Manual of Mental Disorders (PDF here). It faces issue such as the 40-fold jump in diagnosis of childhood bipolar disorder from 1994 to 2003. Some clips from the article:

We still don’t know how much of this increase represents long-overdue care of mentally ill youth and how much comes from facile labeling of youngsters who are merely irritable and moody...Part of the confusion stems from the lack of a discrete definition of juvenile bipolar illness in the diagnostic manual. But there is a deeper problem: despite the great progress being made in neuroscience, we still don’t have a clear picture of the brain mechanisms underlying bipolar illness — or most other mental illnesses... many patients meet several diagnostic definitions at once. Roughly half of adults with clinical depression, for example, also have symptoms that fit the definition of an anxiety disorder...the link between diagnosis and treatment is relatively weak. Antidepressants like Prozac help treat not only depression but also panic disorder, obsessive-compulsive disorder, bulimia and social phobia. This explains why clinicians often treat by symptom rather than diagnosis. Paranoia, for example, is treated with an antipsychotic drug whether it occurs in the context of schizophrenia, bipolar illness or methamphetamine use.

An updated manual..is unlikely to transform treatment substantially — after all, revising diagnoses is still just another way to describe mental conditions we don’t fully understand. But these refinements may well stimulate valuable new inquiry, enabling swifter progress in understanding the mechanisms of disease, better deployment of treatments we have and more efficient discovery of new ones.

Walking the Walk

A new study of human locomotion shows a pattern of changes in independent neural controllers for left and right legs. Here is the abstract from Choi and Bastian and a summary figure from the review by Miall.

Human walking is remarkably adaptable on short and long timescales. We can immediately transition between directions and gait patterns, and we can adaptively learn accurate calibrations for different walking contexts. Here we studied the degree to which different motor patterns can adapt independently. We used a split-belt treadmill to adapt the right and left legs to different speeds and in different directions (forward versus backward). To our surprise, adults could easily walk with their legs moving in opposite directions. Analysis of aftereffects showed that walking adaptations are stored independently for each leg and do not transfer across directions. Thus, there are separate functional networks controlling forward and backward walking in humans, and the circuits controlling the right and left legs can be trained individually. Such training could provide a new therapeutic approach for correcting various walking asymmetries.

Four neural systems are postulated, controlling forward (FW) and backward (BW) walking in left and right legs.
(a) In forward split-belt training, indicated by the dashed box, the right belt is faster than the left, inducing relative changes in the left and right forward-walking circuits (dotted circles). When walking on the tied-belt was tested after adaptation, an aftereffect was seen in forward walking, but not in backward walking. (b,c) In hybrid adaptive walking (b, diagonal dashed box), the left leg is on the slow backward belt and the right leg on the fast forward belt. This induced changes that were evident as aftereffects in both forward and backward walking, and that were compatible with this model of four functionally separate controllers, but were incompatible with a model (c, arrows) in which functional connections between these controllers are modified by learning.

Roles of parietal and prefrontal cortex in working memory

Champod and Petrides distinguish monitoring and manipulation tasks carried out by working memory and demonstrate different brain correlates. Their abstract, and a figure:

Numerous functional neuroimaging studies reported increased activity in the middorsolateral prefrontal cortex (MDLFC) and the posterior parietal cortex (PPC) during the performance of working memory tasks. However, the role of the PPC in working memory is not understood and, although there is strong evidence that the MDLFC is involved in the monitoring of information in working memory, it is also often stated that it is involved in the manipulation of such information. This event-related functional magnetic resonance imaging study compared brain activity during the performance of working memory trials in which either monitoring or manipulation of information was required. The results show that the PPC is centrally involved in manipulation processes, whereas activation of the MDLFC is related to the monitoring of the information that is being manipulated. This study provides dissociation of activation in these two regions and, thus, succeeds in further specifying their relative contribution to working memory.

Figure: Activity in the manipulation minus monitoring and in the monitoring minus manipulation comparisons. Cortical surface renderings in standard stereotaxic space of a subject's brain are shown on the left. (a) Increased activity in the left IPS obtained from the manipulation minus monitoring comparison. The vertical blue line on the left hemisphere cortical surface rendering indicates the anteroposterior level of the coronal section illustrated on the right. (b) Increased activity in the right MDLFC obtained from the monitoring minus manipulation comparison. The vertical green line on the right hemisphere cortical surface rendering indicates the anteroposterior level of the coronal section illustrated on the right side. CS, central sulcus; PoCS, postcentral sulcus; PCS, precentral sulcus; SFS, superior frontal sulcus; IFS, inferior frontal sulcus; MFS, middle frontal sulcus.

The obsession with inhibiting aging...

Coming upon the website of the Methuselah Foundation and the Methuselah Mouse prize begins to bring out the curmudgeon in me. I'm fine with prolonging vitality thought better understanding of the chemistry of aging (check out BrainReady.com, and previous lists of anti-aging sites I've put on the blog, check blog category "aging"), but fantasies about immortality strike me a pure hubris. Contra Dylan Thomas, I think we bloody ought to go gently into that good night, once we've done a good turn here....

Daytime sleep consolidates motor memory

Here is the abstract from Korman et al. :

Two behavioral phenomena characterize human motor memory consolidation: diminishing susceptibility to interference by a subsequent experience and the emergence of delayed, offline gains in performance. A recent model proposes that the sleep-independent reduction in interference is followed by the sleep-dependent expression of offline gains. Here, using the finger-opposition sequence–learning task, we show that an interference experienced at 2 h, but not 8 h, following the initial training prevented the expression of delayed gains at 24 h post-training. However, a 90-min nap, immediately post-training, markedly reduced the susceptibility to interference, with robust delayed gains expressed overnight, despite interference at 2 h post-training. With no interference, a nap resulted in much earlier expression of delayed gains, within 8 h post-training. These results suggest that the evolution of robustness to interference and the evolution of delayed gains can coincide immediately post-training and that both effects reflect sleep-sensitive processes.

And here is a graphic summarizing the results from the review by Diekelmann and Born:

Two ways of consolidating memory of finger tapping skill.
(a) Evolution of finger-to-thumb tapping skill under three experimental key conditions. From top to bottom: after training a specific sequence (Sequence A) in the morning and a first retest 8 h later, a distinct gain in performance developed at the second retest following overnight sleep (purple). Interference by training on a different sequence (Sequence B) 2 h after training of Sequence A completely abolished any sleep-dependent overnight gain developing between the first and second retest (blue). This overnight gain was restored when subjects napped for 90 min between training of Sequence A and interference training on Sequence B (green). (b) Model of skill memory consolidation. Representations of finger tapping skill are encoded in a temporary store. Stabilization (resistance to interference) of the representation can be achieved either through time-dependent synaptic consolidation (dark green) in the temporary buffer or through sleep-dependent system consolidation (red) that leads to a redistribution of the representation to different neuronal networks for long-term storage. Memory enhancement (delayed gains in performance) requires sleep-dependent system consolidation.

Fly brains/Human brains - similarities in sleep induction

Some membrane signaling pathways important in initiating sleep appeared in a common ancestor of humans and insects! Here is the abstract from Foltenyi et al. (the pathways are complicated, but you can get the over all idea):

Epidermal growth factor receptor (EGFR) signaling in the mammalian hypothalamus is important in the circadian regulation of activity. We have examined the role of this pathway in the regulation of sleep in Drosophila melanogaster. Our results demonstrate that rhomboid (Rho)- and Star-mediated [ed. note - these are proteases] activation of EGFR and ERK signaling increases sleep in a dose-dependent manner, and that blockade of rhomboid (rho) expression in the nervous system decreases sleep. The requirement of rho for sleep localized to the pars intercerebralis, a part of the fly brain that is developmentally and functionally analogous to the hypothalamus in vertebrates. These results suggest that sleep and its regulation by EGFR signaling may be ancestral to insects and mammals.

And a graphic from the review by Colwell:

Proposed role of extracellular signal–regulated kinase (ERK) in the regulation of sleep in Drosophila.
(a) Rho-mediated activation of ERK signaling increases sleep duration. During the night, Rho activation in the pars intercerebralis (PI) leads to the production and secretion of an EGFR ligand. The resulting phosphorylation of EGFR activates ERK in the tritocerebrum (TriC). Although the final targets of this signaling pathway are not known, the phosphorylated ERK seems to stay in the processes of the TriC neurons and may well regulate electrical activity and synaptic transmission in these neurons. (b) During wakefulness, Rho signaling in the PI is proposed to be downregulated, resulting in basal levels of ERK signaling. Inhibition of Rho expression in PI neurons results in decreased sleep levels, with short, fragmented sleep bouts. This observation suggests that these mutant flies have an increased need for sleep but are unable to stay asleep (making them a fly model of insomnia).