Brain States

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Parenting Behaviors are Controlled by Specific Neurons in Mice


Parents of newborns can likely sympathize with the diametrically opposed behaviors that mice and rats display towards young pups. On one hand, there is the urge to care for the pups by nesting with and grooming them. On the other hand, there is a darker urge: to go on the attack.

For laboratory mice, the urge that wins out is largely determined by both sex and mating status. Both virgin and mated adult females primarily care for young with very little attacking. This is true for males that have mated, too- especially if it has been about three weeks since they mated, which coincides with the gestation period for mice. Virgin males, however, are more moved by the darker urges- and with solid evolutionary reason. If they haven’t mated, then there is no possibility that the pups are theirs.

At Harvard University, Zheng Wu and his colleagues set out to find the neural circuits that control these behaviors. Their results were published this week in the journal Nature.

Mice, like many other species, use the vomeronasal organ to sense pheromones given off by others of their species, and pheromones can be a powerful cue in motivating social behaviors.  Wu and his colleagues tested the idea that these pheromonal inputs could be triggering the pup-directed aggression in virgin males.  They compared virgin males with intact, healthy vomeronasal organs to males who had impaired vomeronasal function thanks to a genetic mutation in a key pheromone receptor. Amazingly, they found that the virgin males who couldn’t smell the pheromones were not aggressive toward pups, and actually started to build nests and care for them.

The researchers next wanted to find the neural populations that could underlie parenting behaviors. They identified a set of neurons in the medial preoptic area that became active in females and sexually experienced males after they started parenting. These same neurons stayed silent in virgin males. The medial preoptic area is a part of the hypothalamus, which is one of the areas that the vomeronasal organ sends information to.

Although the medial preoptic area is small, it still contain many different types of cells. Which ones were responsible for getting the mice to act like parents? To answer this question, the scientist looked at the types of neurotransmitters made by cells in the preoptic area, and concluded that the cells active during parenting overlapped the most with cells that make a small neurotrasmitter known as Galanin.

Wu and colleagues investigated the role of these neurons using two opposing manipulations.

In the first set of experiments, they destroyed these neurons using modern genetic targeting tools. When they destroyed the cells in virgin females, they abruptly switched from caring for pups to attacking them. This suggesting that at least for  virgin females, these neurons act as the switch between these two opposing behaviors.  For sexually experienced males and females, loss of the galanin-positive neurons only resulted in a loss of parenting behaviors without an increase in aggression.

In the second set of experiments, the researchers activated the galanin-positive neurons by making them sensitive to light. Whenever a virgin male made contact with a pup, the researchers shined light through a optic fiber onto these neurons, thus turning them on. When the neurons were active, virgin males only attacked the pups about 10% of the time – but if the researchers left the light off, the same mice would attack over 90% of the time.

In mated male fathers, the same light-induced activity in the neurons caused a marked increase in grooming of the pups.

The authors concluded that the neural circuits to care for or attack young pups co-exist simultaneously in the mouse brain, and which circuit is active depends largely on a social context – working through a set of hypothalamic neurons.

Parental care is required for newborns to survive in many species. This is especially true for mammals, because our young are born relatively helpless and require adult intervention to move and find food.  Between species,  it varies widely how much of the care is provided by the mother or the father.  This work demonstrates that both sexes have the neuronal architecture necessary for effective parenting.

There is good reason to believe that humans have a similar set of neurons controlling parenting behaviors, because other neurons in the medial preoptic area have been shown to have conserved functions across mammal species.  This work sets the stage to investigate other fascinating questions, such as whether the function of these neurons is disrupted in postpartum depression.

REFERENCE: Galanin neurons in the medial preoptic area govern parental behaviour. (2014) Zheng Wu, Anita E. Autry, Joseph F. Bergan, Mitsuko Watabe-Uchida & Catherine G. Dulac. Nature 509, 325–330.

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What Can Dreams Tell Us About Consciousness?

893666_45846960To understand the nature of consciousness is perhaps the holy grail of neuroscience, not to mention philosophy and psychology. Although we are a long way off from that goal, current studies can give us some insight into our own awareness by examining and manipulating the brain during lucid dreaming.

In lucid dreaming, the dreamer is aware that he or she is dreaming while the dream continues. Lucid dreaming is also associated with several other dream states, including being able to control the dream or taking on a third person perspective. The dreamer may experience dream events,  but also have access to waking memories.

Scientists have reported that the brains of people who are in a state of lucid dreaming exhibit a phenomenon known as phase synchrony. This means that the neurons in the brain are synchronizing with each other and firing with a particular common frequency. Oscillations (or colloquially, waves) of certain frequencies are grouped together and named with greek letters, and different frequencies correspond with different states. For example, the characteristic frequency for a state of relaxed wakefulness is in the alpha band of about 8-13 Hz.  During lucid dreaming, there is an increase in the gamma band of frequencies, corresponding to about 40 Hz. This increase happens especially in the frontal an temporal lobes of the brain.

For many years, scientists have wondered whether these synchronized brain waves are a cause of the self-awareness in lucid dreams, or a consequence.  A new study out this week, spearheaded by neuroscientist Ursula Voss, sought to address this question by passing alternating current at a variety of frequencies between two electrodes placed on the surface of the scalp. Voss and her team waited until their human volunteers were dreaming in a state of REM sleep for at least two minutes before starting to apply the current, which they hoped would entrain the neurons in the brain to the same frequency as they used for stimulation. After stimulating for 30 seconds, they woke the dreamers up and asked them questions about their dreams.

When the scientists stimulated the brain with a 25 or a 40 Hz current, similar to what is observed in gamma waves, the subjects reported an increase in lucidity compared to other stimulation frequencies. Here is how one subject described it:

“I was dreaming about lemon cake. It looked translucent, but then again, it didn’t. It was a bit like in an animated movie, like the Simpsons. And then I started falling and the scenery changed and I was talking to Matthias Schweighöfer (a German actor) and 2 foreign exchange students. And I was wondering about the actor and they told me ‘yes, you met him before,’ so then I realized ‘oops, you are dreaming.’ I mean, while I was dreaming! So strange!”

This study represents a huge moment for neuroscience, because it is the first report that transcranial stimulation is capable of causing an alteration in conscious awareness. Moreover, this study suggest that brainwaves of the 40Hz band are not simply a feature of higher cognitive functions, but can actually cause them. Strange indeed.

Reference: Induction of self awareness in dreams through frontal low current stimulation of gamma activity. (2014) Ursula Voss, Romain Holzmann, Allan Hobson, Walter Paulus, Judith Koppehele-Gossel, Ansgar Klimke & Michael A Nitsche. Nature Neuroscience. 

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Fear Perception Depends on Heartbeat Cycle Timing


It always amazes me how much our reactions to the world depend on our internal states, even when those states are outside of our conscious awareness. Though we don’t typically consider it a sense like hearing or seeing, the visceral sense is real: there are tons of receptors inside us, monitoring our internal physiology at all times.

One example is the baroreceptors that monitor the pressure inside our arteries as the heart pumps blood through them. The baroreceptors have a major role in the regulation of blood pressure, as one might expect. However, recent research has revealed that information from these internal receptors is also being used when we process emotional stimuli.

Sarah Garfinkle and colleagues investigated this phenomenon recently by showing people images of human faces, either displaying the emotions of fear, disgust, or happiness, or in a neutral state of repose. The facial expressions were embedded in a stream of scrambled images, and were flashed by so quickly that they were at the limit of conscious perception: each frame occupied the screen for a mere 70 milliseconds, or less than a tenth of a second. The facial expressions were timed to coincide with the cardiac cycle, either landing at systole (between the “lub” and “dub” of a heartbeat, when arterial pressure is high) or at diastole (between heartbeats, when arterial pressure is low).

Afterward, participants were asked to identify which face they had seen in a lineup of three faces. In general, the participants were pretty bad at this test, getting it right only about half the time. But for fearful faces especially, participants were much better at picking out the face they had seen when they saw it in the middle of the heartbeat, rather than between them. Being at the “right” time with respect to the heartbeat pushed detection of the fearful face over the edge from subconscious into consciousness.

So people were better able to detect a fearful face when it came in the middle of a heartbeat, but what about how people thought of the face they saw? The scientists assessed this in a separate experiment, at the same time doing functional neuroimaging on the participants to see what their brains were doing. Again, they showed participants a fearful face, either timed to coincide with systole or diastole. This time, the face was on the screen for a bit longer, so the participants were sure to detect it. Afterward the experimenters asked the participants to rate the intensity of the emotion they saw.

Again, the results depended on the heartbeat cycle timing: if the face was presented in the middle of a heartbeat, participants rated it as more fearful than if it was presented between heartbeats.  The difference was not just perceptual, but also was evident in the activity of a brain structure called the amygdala. The amygdala is known be involved in the processing of emotion, and this area was more active when the participants saw the fearful face at systole than at diastole.

Interestingly, this effect was less marked for individuals who were anxious. People with high anxiety conditions like PTSD are more responsive to fearful stimuli, regardless of when it comes with respect to the cardiac cycle.

This work is just one example of the dynamic feedback between our physiological and emotional states. For decades, neuroscientists have debated the nature of emotions: does nervousness cause butterflies in the stomach, or do butterflies in the stomach create the feeling of nervousness? Which comes first, the physiological or the psychological? We may never have a clear-cut answer to this question, because the there may not be a clear-cut answer. It seems that the road between the body and the mind is a two-way street.

Reference: Fear from the Heart: Sensitivity to Fear Stimuli Depends on Individual Heartbeats. (2014) Sarah N. Garfinkel, Ludovico Minati, Marcus A. Gray, Anil K. Seth, Raymond J. Dolan, and Hugo D. Critchley. Journal of Neruoscience 34(19): 6573-6582