Dopamine seems to be having a moment in the zeitgeist. You may have read about it in the news^[1], seen viral social media posts^[2] about “dopamine hacking” or listened to podcasts^[3] about how to harness what this molecule is doing in your brain to improve your mood and productivity. But recent neuroscience research suggests that popular strategies to control dopamine are based on an overly narrow view of how it functions.

Dopamine is one of the brain’s neurotransmitters^[4] – tiny molecules that act as messengers between neurons. It is known for its role in tracking your reaction to rewards such as food, sex, money or answering a question correctly. There are many kinds of^[5] dopamine neurons^[6] located in the uppermost region of the brainstem that manufacture and release dopamine throughout the brain. Whether neuron type affects the function of the dopamine it produces has been an open question.

Recently published research reports a relationship between neuron type and dopamine function, and one type of dopamine neuron has an unexpected function^[7] that will likely reshape how scientists, clinicians and the public understand this neurotransmitter.

Dopamine neuron firing

Dopamine is famous for the role it plays in reward processing, an idea that dates back at least 50 years^[8]. Dopamine neurons monitor the difference between the rewards you thought you would get from a behavior and what you actually got. Neuroscientists call this difference a reward prediction error^[9].

Eating dinner at a restaurant that just opened and looks likely to be nothing special shows reward prediction errors in action. If your meal is very good, that results in a positive reward prediction error, and you are likely to return and order the same meal in the future. Each time you return, the reward prediction error shrinks until it eventually reaches zero when you fully expect a delicious dinner. But if your first meal was terrible, that results in a negative reward prediction error, and you probably won’t go back to the restaurant.

Dopamine neurons communicate reward prediction errors to the brain through their firing rates and patterns of dopamine release, which the brain uses for learning^[10]. They fire in two ways^[11].

Phasic firing refers to rapid bursts that cause a short-term peak in dopamine. This happens when you receive an unexpected reward or more rewards than anticipated, like if your server offers you a free dessert or includes a nice note and smiley face on your check. Phasic firing encodes reward prediction errors.

By contrast, tonic firing describes the slow and steady activity of these neurons when there are no surprises; it is background activity interspersed with phasic bursts. Phasic firing is like mountain peaks, and tonic firing is the valley floors between peaks.

Dopamine functions

Tracking information used in generating reward prediction errors is not all dopamine does. I have been following all the other jobs of dopamine with interest^[14] through^[15] my own^[16] research measuring^[17] brain areas where dopamine neurons are located in people.

About 15 years ago, reports started coming out that dopamine neurons respond to^[18] aversive events^[19] – think brief discomforts like a puff of air against your eye, a mild electric shock or losing money – something scientists thought dopamine did not do^[20]. These studies showed that some dopamine neurons respond only to rewards while others respond to both rewards and negative experiences, leading to the hypothesis that there might be more than one dopamine system^[21] in the brain.

These studies were soon followed by experiments showing that there is more than one type of dopamine neuron. So far, researchers have identified seven distinct types^[22] of dopamine neurons by looking at their genetic profiles.

A study published in August 2023 was the first to parse dopamine function based on neuron subtype^[23]. The researchers at the Dombeck Lab^[24] at Northwestern University examined three types of dopamine neurons and found that two tracked rewards and aversive events while the third monitored movement, such as when the mice they studied started running faster.

Dopamine release

Recent media coverage on how to control dopamine’s effects is based only on the type of release that looks like peaks and valleys. When dopamine neurons fire in phasic bursts, as they do to signal reward prediction errors, dopamine is released throughout the brain. These dopamine peaks happen very fast^[25] because dopamine neurons can fire many times in less than a second.

There is another way that dopamine release happens: Sometimes it increases slowly until a desired reward is obtained. Researchers discovered this ramp pattern^[26] 10 years ago in a part of the brain called the striatum. The steepness of the dopamine ramp tracks how valuable a reward is and how much effort it takes to get it. In other words, it encodes motivation.

The restaurant example can also illustrate what happens when dopamine release occurs in a ramping pattern. When you have ordered a meal you know is going to be amazing and are waiting for it to arrive, your dopamine levels are steadily increasing. They reach a crescendo when the server places the dish on your table and you sink your teeth into the first bite.

How dopamine ramps happen is still unsettled, but this type of release is thought to underlie goal pursuit and learning^[29]. Future research on dopamine ramping will affect how scientists understand motivation and will ultimately improve advice on how to optimally hack dopamine.

Dopamine(s) in disease and neurodiversity

Though dopamine is known for its involvement in drug addiction^[30], neurodegenerative disease^[31] and neurodevelopmental conditions^[32] like attention-deficit/hyperactivity disorder, recent research suggests how scientists understand its involvement may soon need updating. Of the seven subtypes of dopamine neurons that are known so far, researchers have characterized the function of only three.

There is already some evidence that the discovery of dopamine diversity is updating scientific knowledge of disease. The researchers of the recent paper identifying the relationship between dopamine neuron type and function point out that movement-focused dopamine neurons^[33] are known to be among the hardest hit in Parkinson’s disease, while two other types are not as affected. This difference might lead to more targeted treatment options.

Ongoing research untangling the diversity of dopamine will likely continue to change, and improve, our understanding of disease and neurodiversity.

NASA’s independent study team^[1] released its highly anticipated report^[2] on UFOs on Sept. 14, 2023.

In part to move beyond the stigma often attached to UFOs^[3], where military pilots fear ridicule or job sanctions if they report them, UFOs are now characterized by the U.S. government as UAPs, or unidentified anomalous phenomena.

Bottom line: The study team found no evidence that reported UAP observations are extraterrestrial.

I’m a professor of astronomy^[4] who has written extensively on astrobiology^[5] and the scientists^[6] who search for life in the universe. I have long been skeptical of the claim^[7] that UFOs represent visits by aliens to Earth.

From sensationalism to science

During a press briefing^[8], NASA Administrator Bill Nelson^[9] noted that NASA has scientific programs to search for traces of life on Mars^[10] and the imprints of biology^[11] in the atmospheres of exoplanets. He said he wanted to shift the UAP conversation from sensationalism to one of science.

With this statement, Nelson was alluding to some of the more outlandish claims about UAPs and UFOs. At a congressional hearing in July^[12], former Pentagon intelligence officer David Grusch testified^[13] that the American government has been hiding evidence of crashed UAPs and alien biological specimens. Sean Kirkpatrick^[14], head of the Pentagon office charged with investigating UAPs, has denied these claims.

And the same week NASA’s report came out, Mexican lawmakers^[15] were shown by journalist Jaime Maussan two tiny, 1,000-year-old bodies that he claimed were the remains of “non-human” beings. Scientists have called this claim fraudulent^[16] and say the mummies may have been looted from gravesites in Peru.

Conclusions from the report

The NASA study team report sheds little light on whether some UAPs are extraterrestrial. In his comments, the chair of the study team, astronomer David Spergel^[17] stated that the team had seen “no evidence to suggest that UAPs are extraterrestrial in origin.”

Of the more than 800 unclassified sightings collected by the Department of Defense’s All-domain Anomaly Resolution Office^[18] and reported at the NASA panel’s first public meeting^[19] back in May 2023, only “a small handful cannot be immediately identified as known human-made or natural phenomena,” according to the report^[20].

Many of the recent sightings^[21] can be attributed to weather balloons and airborne clutter. Historically, most UFOs are astronomical objects^[22] such as meteors, fireballs^[23] and the planet Venus^[24].

Some sightings represent surveillance operations^[25] by foreign powers, which is why the U.S. military considers this a national security issue^[26].

The report does offer recommendations to NASA on how to move these investigations forward.

Most of the UAP data considered by the study team comes from U.S. military aircraft. Analysis of this data is “hampered by poor sensor calibration, the lack of multiple measurements, the lack of sensor metadata, and the lack of baseline data.” The ideal set of measurements would include optical imaging, infrared imaging, and radar data, but very few reports have all these.

The NASA study team described in the report the types of data that can shed more light on UAPs. The authors note the importance of reducing the stigma that can cause both military and commercial pilots to feel that they cannot freely report sightings. The stigma stems from decades of conspiracy theories tied to UFOs^[27].

The NASA study team suggests gathering sightings by commercial pilots using the Federal Aviation Administration and combining these with classified sightings not included in the report. Team members did not have security clearance, so they could look only at the subset of military sightings that were unclassified. At the moment, there is no anonymous nationwide UAP reporting mechanism for commercial pilots.

With access to these classified sightings and a structured mechanism for commercial pilots to report sightings, the All-domain Anomaly Resolution Office^[28] – the military office charged with leading the analysis effort – could have the most data.

NASA also announced^[29] the appointment of a new director of research on UAPs. This position will oversee the creation of a database with resources to evaluate UAP sightings.

Looking for a needle in a haystack

Parts of the briefing resembled a primer on the scientific method. Using analogies, officials described the analysis process as looking for a needle in a haystack, or separating the wheat from the chaff. The officials said they needed a consistent and rigorous methodology for characterizing sightings, as a way of homing in on something truly anomalous.

Spergel said the study team’s goal was to characterize the hay – or the mundane phenomena – and subtract it to find the needle, or the potentially exciting discovery. He noted that artificial intelligence can help researchers comb through massive datasets to find rare, anomalous phenomena. AI is already being used this way in many areas of astronomy research^[30].

The speakers noted the importance of transparency. Transparency is important because UFOs have long been associated with conspiracy theories and government cover-ups^[31]. Similarly, much of the discussion during the congressional UAP hearing^[32] in July focused on a need for transparency. All scientific data that NASA gathers is made public on various websites, and officials said they intend to do the same with the nonclassified UAP data.

At the beginning of the briefing^[33], Nelson gave his opinion that there were perhaps a trillion instances of life beyond Earth. So, it’s plausible that there is intelligent life out there. But the report says that when it comes to UAPs, extraterrestrial life must be the hypothesis of last resort. It quotes Thomas Jefferson: “Extraordinary claims require extraordinary evidence.” That evidence does not yet exist.

China^[1], India^[2] and the U.S.^[3] have all achieved landing on the Moon in the 2020s.

Once there, their eventual goal is to set up a base^[4]. But a successful base – along with the spacecraft that will carry people to it – must be habitable for humans. And a big part of creating a habitable base is making sure the heating and cooling systems work.

That’s especially true because the ambient temperature of potential places for a base can vary widely. Lunar equatorial temperatures^[5] can range from minus 208 to 250 degrees Farenheit (minus 130 to 120 degrees Celsius) – and similarly, from minus 225 F to 70 F (minus 153 C to 20 C) on Mars^[6].

In 2011, the National Academies of Science published a report^[7] outlining research in the physical and life sciences that scientists would need to do for the U.S. space program to succeed. The report emphasized the need for research about building heating and cooling systems for structures in space.

I’m an engineering professor^[8], and when that report came out, I submitted a research proposal to NASA. I wanted to study something called the liquid-vapor phenomenon. Figuring out the science behind this phenomenon would help with these big questions around keeping structures in space a comfortable and habitable temperature.

Over a decade after we submitted a proposal, my team’s project is now being tested on the International Space Station.

Going with the ‘flow’

Liquid-vapor systems – or two-phase systems – involve the simultaneous flow of liquid and vapor^[9] within a heating or cooling system. While many commercial air conditioners and refrigeration systems on Earth use two-phase systems, most systems used in spacecraft and on the International Space Station are purely liquid systems – or one-phase systems.

In one-phase systems, a liquid coolant moves through the system and absorbs excess heat, which raises the liquid’s temperature. This is similar to the way cars use radiators to cool^[10]. Conversely, heated liquid in the system would eject the heat out to the ambient area, lowering the liquid’s temperature to its initial level.

But liquid-vapor systems could transfer heat more effectively^[11] than these one-phase systems, and they’re much smaller and lighter than purely liquid systems. When traveling in space, you have to carry everything on the craft with you, so small and light equipment is essential.

There are two key processes that happen in a closed, two-phase liquid-vapor system. In one, the liquid changes to a vapor during a process called “flow boiling^[12].” Just like boiling water on the stove, in flow boiling the liquid heats up and evaporates.

In systems used in space, the two-phase mixture passes through heat exchange components that transfer the heat generated from electronics, power devices and more into the mixture. This gradually increases the amount of vapor produced as the system absorbs heat and converts liquid to vapor.

Then, there’s flow condensation^[13], in which the vapor cools and returns to a liquid. During flow condensation, heat leaves the system by radiating out into space.

Scientists control these two processes in a closed loop^[14] so they can extract and use the heat that’s released during condensation. In the future, this technology could be used to control temperature in spacecraft going to the Moon, Mars or beyond, or even in settlements or habitats on the lunar and Martian surfaces.

Building and testing

With the grant from NASA to do this work, I designed an experimental program called the “Flow Boiling and Condensation Experiment^[15].” My team built a fluid management system for the experiment and two test modules: one that helped us test flow boiling and one that helped us test flow condensation.

Right now, the equipment used for heating and cooling^[17] in space was designed based on experiments in Earth’s gravity. Our flow boiling and condensation experiment seeks to change that.

First, we tested^[18] whether the system and modules we built worked when subjected to Earth’s gravity. Once we learned they did, we sent them up in a parabolic flight aircraft^[19]. This craft simulated reduced gravity^[20] so we could get an idea of how the system performed in an environment similar to that of space.

In August 2021 we completed the flow boiling module and launched it to the International Space Station for testing in zero gravity^[21]. By July 2022 we’d completed the boiling experiments. In August 2023 the flow condensation module followed, and we’ll start working on the final condensation tests soon.

Responding to reduced gravity

Liquid-vapor flow systems^[22] are far more sensitive to gravity than the purely liquid systems used now, so it’s harder to design ones that work under reduced gravity.

The mechanism behind these systems has to do with the motion of liquid relative to the vapor, and what that motion looks like depends on a concept called buoyancy^[23].

Buoyancy is determined by gravity as well as the density difference between liquid and vapor. So any change in gravity affects the system’s buoyancy, and thus the movement of the vapor relative to the liquid.

In space, there are also different strengths of gravity that the systems might need to operate under. Space vehicles experience microgravity^[24] – near weightlessness – while a lunar habitat would operate under gravity conditions about one-sixth the strength of Earth’s gravity^[25], and a Martian habitat would be operating under gravity three-eighths the strength^[26] of Earth’s gravity.

Our team is working on designing flow boiling and condensation models that can work under all these levels of reduced gravity.

Applications for space habitats

This equipment could one day go into a human habitat on the Moon or Mars, where it would help maintain comfortable temperatures for people and machinery inside. A heat pump^[27] using our flow boiling and flow condensation systems could extract the heat that astronauts and their machines give off. It would then send this collected heat out of the habitat to keep the inside cool – similar to the way air conditioners on Earth work.

The temperatures in space can be extreme and hostile to people, but with these technologies, my team might one day help create craft and habitats that allow people to explore the Moon and beyond.

Few beverages have as rich a heritage and as complicated a chemistry as bourbon whiskey, often called “America’s spirit^[1].” Known for its deep amber hue and robust flavors, bourbon has captured the hearts^[2] of enthusiasts across the country^[3].

But for a whiskey to be called a bourbon, it has to adhere to very specific rules^[4]. For one, it needs to be made in the U.S. or a U.S. territory – although almost all is made in Kentucky. The other rules have more to do with the steps to make it – how much corn is in the grain mixture, the aging process and the alcohol proof.

I’m a bourbon researcher^[5] and chemistry professor^[6] who teaches classes on fermentation, and I’m a bourbon connoisseur myself. The complex science^[7] behind this aromatic beverage reveals why there are so many distinct bourbons, despite the strict rules around its manufacture.

The mash bill

All whiskeys have what’s called a mash bill. The mash bill refers to the recipe of grains that makes up the spirit’s flavor foundation. To be classified as bourbon, a spirit’s mash bill must have at least 51% corn^[8] – the corn gives it that characteristic sweetness.

Almost all bourbons also have malted barley, which lends a nutty, smoky flavor and provides enzymes that turn starches into sugars^[9] later in the production process.

Many distillers also use rye and wheat^[10] to flavor their bourbons. Rye makes the bourbon spicy, while wheat produces a softer, sweeter flavor. Others might use grains like rice or quinoa^[11] – but each grain chosen, and the amount of each, affects the flavor down the line.

The chemistry of yeast

Once distillers grind the grains from the mash bill and mix them with heated water, they add yeast to the mash. This process is called “pitching the yeast.” The yeast consumes sugars and produces ethyl alcohol and carbon dioxide as byproducts during the process called fermentation – that’s how the bourbon becomes alcoholic^[12].

The fermented mash is now called “beer.” While similar in structure and taste to the beer you might buy in a six-pack, this product still has a way to go before it reaches its final form.

Yeast fermentation yields other byproducts besides alcohol and carbon dioxide, including flavor compounds called congeners^[13]. Congeners can be esters, which produce a fruity or floral flavor, or complex alcohols, which can taste strong and aromatic.

The longer the fermentation period, the longer the yeast has to create more flavorful byproducts^[14], which enhances the complexity of the spirit’s final taste. And different yeasts produce different amounts of congeners^[15].

Separating the fermentation products

During distillation, distillers separate the alcohol and congeners from the fermented mash of grains, resulting in a liquid spirit. To do this, they use pot or column stills^[16], which are large kettles or columns, respectively, often made at least partially of copper. These stills heat the beer and any congeners that have a boiling point of less than 350 degrees Fahrenheit (176 degrees Celsius) to form a vapor.

The type of still^[18] will influence the beverages’ final flavor, because pot stills often do not separate the congeners as precisely as column stills do. Pot stills result in a spirit that often contains a more complex mixture of congeners^[19].

The desired vapors that exit the still are condensed back to liquid form, and this product is called the distillate^[20].

Different chemical compounds have different boiling points, so distillers can separate the different chemicals by collecting the distillate at different temperatures^[22]. So in the case of the pot still, as the kettle is heated, chemicals that have lower boiling points are collected first. As the kettle heats further, chemicals with higher boiling points vaporize and then are condensed and collected^[23].

By the end of the distillation process with a pot still, the distillate has been divided into a few fractions^[24]. One of these fractions is called the “hearts^[25],” containing mostly ethanol and water, but also small amounts of congeners, which play a big role in the final flavor of the product.

The alchemy of time and wood

After distillation, the “hearts” fraction (which is clear and resembles water) is placed in a charred oak barrel for the aging process. Here, the bourbon interacts with chemicals in the barrel’s wood, and about 70% of the bourbon’s final flavor^[26] is determined by this step. The bourbon gets all its amber color during the aging process.

Bourbon may rest in the barrel for several years. During the summer, when the temperature is hot, the distillate can pass through the inner charred layer of the barrel. The charred wood acts like a filter and strains out^[27] some of the chemicals before the distillate seeps into the wood. These chemicals bind to the charred layer and do not release, kind of like a water filter.

Under the charred layer of the barrel is a “red line,” a layer where the oak was toasted during the charring process of making the barrel. The toasting process breaks down starch and other polymers^[29], called lignins and tannins, in the oak.

When the distillate seeps to the red-line layer, it dissolves the sugars^[30] in the barrel, as well as lignin byproducts and tannins.

During the cold winter months, the distillate retreats back into the barrel, but it takes with it these sugars, tannins and lignin byproducts from the wood, which enhance the flavors. If you disassemble a barrel after it has aged bourbon, you can see a “solvent line^[31],” which shows how far into the wood the distillate penetrated. The type of oak barrel can have a profound effect on the final taste, along with the barrel’s size and how charred it is.

For most distilleries, barrels are stored in large buildings called rickhouses^[32]. Ethyl alcohol and water in the distillate evaporate out of the barrel, and the humidity in that part of the rickhouse plays a big role.

Lower humidity often leads to higher-proof bourbon, as more water than ethanol leaves the barrel. In addition, air enters the barrel, and oxygen from the air reacts with some of the chemicals in the bourbon, creating new flavor chemicals. These reactions tend to soften the taste^[33] of the final product.

There are thousands of bourbons^[34] on the market, and they can be distinguished by their unique flavors and aromas. The variety of brands reflects the many choices that distillers make on the mash bill, fermentation and distillation conditions, and aging process. No two bourbons are quite the same.

Apple announced on Sept. 12, 2023, that it plans to adopt the USB-C connector^[1] for all four new iPhone 15 models, helping USB-C become the connector of choice of the electronics industry, nine years after its debut. The move puts Apple in compliance with European Union law^[2] requiring a single connector type for consumer devices.

USB-C^[3] is a small, versatile connector for mobile and portable devices like laptops, tablets and smartphones. It transfers data at high speeds, transmits video signals and delivers power to charge devices’ batteries. USB stands for Universal Serial Bus. The C refers to the third type, following types A and B.

The USB Implementers Forum^[4], a consortium of over 1,000 companies that promote and support USB technology, developed the USB-C connector to replace the older USB connectors as well as other types of ports like HDMI, DisplayPort and VGA. The aim is to create a single, universal connector for a wide range of devices.

The key features and benefits of USB-C include a reversible connector that you can insert in either orientation. It also allows some cables to have the same connector on both ends for connecting between devices and connecting devices to chargers, unlike most earlier USB and Lightning cables.

USB-C’s widespread adoption in the electronics industry is likely to lead to a universal standard that reduces the need for multiple types of cables and adapters. Also, its slim and compact shape allows manufacturers to make thinner and lighter devices.

USB-C refers to the physical connector. Connectors use a variety of data transfer protocols – sets of rules for formatting and handling data – such as the USB and Thunderbolt protocols. USB-C supports USB and Thunderbolt, which makes it suitable for connecting laptops, smartphones, tablets, monitors, docking stations and many other devices.

The latest USB protocol, version 4^[5], provides a data transfer rate of up to 40 gigabits per second, depending on the rating of the cable. The latest Thunderbolt^[6], also on version 4, supports up to 40 gigabits-per-second data transfer and 100 watts charging. The newly announced Thunderbolt 5^[7] will support up to 80 and 120 gigabits-per-second transfer and 140 to 240 watts power transfer over a USB-C connector.

Due to the fragmented nature of technology evolution, computer users a decade ago were struggling with too many connectors: USB for data; power cables for charging; HDMI, DisplayPort or VGA for video; and Ethernet for internet. This called for an industrywide effort to convergence on an all-purpose connector.

Since its introduction in 2014, USB-C has gained widespread popularity and has already become the connector of choice for most non-Apple devices. Apple converted the iPad Pro to USB-C in 2018 and now is doing the same for the best selling Apple device, the iPhone. Some market forecasts suggest there will be close to 4 billion USB-C connector sales by 2025 and 19 billion by 2033^[8].

Thanks to the industrywide adoption of USB-C, consumers soon won’t have to ask “Is this the right connector?” when they reach for a cable to charge or sync their portable devices. And if you’re an iPhone user and find yourself with a new model, you can [recycle your no-longer-needed Lightning cables] by, for example, bringing them to an Apple store.

There are alien minds among us. Not the little green men of science fiction, but the alien minds that power the facial recognition in your smartphone, determine your creditworthiness^[1] and write poetry^[2] and computer code^[3]. These alien minds are artificial intelligence systems, the ghost in the machine that you encounter daily.