A new study by psychologist Shantanu Jadhav and his lab shines new light on how rats make decisions based on recent memories.

During sleep, the brain replays each memory from the day in a unique pattern of brain cell firings. The activation of a pattern essentially creates a recording of the memory so it can be stored for the long term.

This process, called memory consolidation, occurs while were awake, too. In a recent paper in Neuron, assistant professor of psychology Shantanu Jadhav and his lab demonstrate how memory consolidation works in rats brains when they make a decision.

With remarkable precision, Jadhav and his team identified and isolated specific patterns of brain cell firings in the animals that corresponded to individual memories. As a result, they could tell what the rodents were remembering. They also found a way to predict what the animals would do next.

In the long term, researchers hope that a greater understanding of how the brain processes memories will lead to treatments for diseases where memory is impaired, such as Alzheimers or other kinds of dementia.

The experiment

Jadhav and his collaborators designed a W-shaped maze. Each prong of the W held small wells with a tasty rat treat. A rat entering the maze on the right would find the nearest treat in the center. After that, the nearest treat would be on the left.

It worked in the opposite direction as well; after noshing on the left, the rodent went to the center and then back to the right. Over the course of 6 to 8 hours, the rats formed separate memories of each of the four parts of a roundtrip journey right to center, center to left, left to center and center to right. Each part corresponded to a unique and identifiable pattern of brain cell firings.

Decision time for the rats

When the rats arrived in the center of the maze, they paused for several seconds. During this time, they pondered their next move. They could go back to where they came from (no treat) or they could continue to the opposite side of the W (treat!).

The scientists monitored the rats decision-making process in real-time. First, the rats replayed the sequence of brain cell firings from a memory of one of the four legs of their journey.

But what surprised the scientists was that the rats' brains played the sequence in reverse order, rewinding the recording of the memory. This process is called reverse replay and enables the rats to recall the past in order to decide what to do next.

The rats also pondered their future. Here, the rats played their memories brain cell firings in the original order in which they occurred in a process called forward replay.

Reverse and forward replay occur in the hippocampus, a seahorse-shaped structure located close to the brain's center. (It actually means seahorse in Greek.) The hippocampus handles spatial memory, which in both rats and humans makes it possible to determine location and navigation from place to place. "It's the internal GPS system for navigation in the mammalian brain," Jadhav said.

The brain firings involved in reverse and forward replay are called sharp-wave ripples. In both rats and humans, they happen in bursts that last a few hundred milliseconds a good thing. It may take an hour to go to work, but if recalling the memory of your route took that long youd never return home.

What will the rat do next?

Jadhav and his fellow researchers wanted to see if they could predict the rats route by analyzing their brain cell firings. They observed that the rats final decision on what route to take next didn't happen in the hippocampus, which only sifted through the options. It was in the prefrontal cortex, located behind the forehead, where the animals future path was determined.

The researchers matched activity in the prefrontal cortex to the four brain firing patterns that occurred during the rats journey. Whichever patterns wound up being activated by the prefrontal cortex indicated the route the animal would travel.

Just before the animals moved on from the center, Jadhav and his team observed the pattern fire, enabling them to foresee the rats' next move. "We could actually predict the rats' future," Jadhav said.

Brandeis graduate students Justin D. Shin and Wenbo Tang co-authored the Neuron paper.This research was funded by the National Institutes of Health, the Alfred P. Sloan Foundation and the Whitehall Foundation.

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The neuroscience behind remembering the past and plotting the future - Brandeis University

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The concept is called reverse inference. Its both neurosciences greatest ambition, and the origin of its most frustratingly breathless overstatements.

Every so often, a person is unexpectedly thrust into a defining wedge-issue of an era. This time, I was asked rhetorically, Is being gay a choice? Well, my friend answered their own question; according to a series of studies, including one published inScientific Reportsin 2018, scientists have discovered neurological differences between gay and straight people. When subjects were shown a series of pornographic pictures, depending on the content of the images, people with different sexual orientations had different brain activity. In other words, there is a concrete biological origin of sexuality; there is such a thing as a gay or straight brainrather, a biologically-inevitably gay or straight brain.

As my friend concluded from this development, this proves that being gay is not simply psychological; theres an actual biology to it. Those in right-wing chatrooms trying to mock gay people by saying things to the effect of, I want to be a frog, therefore, Im a frog are now, scientifically verifiably, jerks. Just as one cant just decide to be a frog, one cannot simply claim to be gay and then, poof, become gay.

Without science, if someone states his or her sexual preference, either he or she is telling the truth or making it up. Either a person is gay or theyre pretending to be. With science, however, maybe this debate can be resolved for good.

Personally, I do not have a strong position on whenin the course of ones developmenta person starts being gay. Ive seen scientific arguments for genetic destiny, but Im also drawn to the idea that sexual preference is slowly shaped by an interplay of genetic and social factors throughout adolescence and even into adulthood.

I do, however, have a position on whether brain-imaging research supports the conclusion that being gay is a biological-inevitability. More importantly, I have a position on whether scientific research can inform our moral obligations towards supporting gay rights. In this essay, I hope to show that in specific, neuroscientific terms, we do not know with much confidence what being gay really is. Furthermore, even if we did, science cannot resolve the LGBTQ-rights aspect of the culture wars.

Brain Imaging Does Not Prove Biological Causation, and, Being LGBT is, in General, More than Sexual Orientation

Despite the involvement of extremely complex brain-recording technology, the design of the 2018 experiment was very simple. Scientists collected a group of people who were gay and another group of people who were straight, positioned them in a brain scanner, and showed them pornography. While the subjects awkwardly looked at naked bodies, researchers collected images of their brain activity, and, lo and behold, discovered that some areas of the brain showed differences.

However, one big issue is that straight people and gay people do not differ just in sexuality. There are also (in general) differences in personalities and lifestyles. What if the brain differences seen in this study are really just differences in social presentation? If being gay is (often) more than sexual preference, we cant be confident that the neurological differences are strictly about sexuality.

This confound is not unique just to studies dealing with sexuality. The way we conduct brain-imaging today struggles to prove causation in a traditional scientific sense. Before scientists are willing to adopt the term causation, they want to see that the manipulation of some variable has an impact on another. In other words, changing X reliably changes Y. Sure, we can compare brain activity between groups; however, we cannot intervene in a way that truly mimics what were recording.

The problem is two-fold. Commonly-used brain-recording technologies like EEG and fMRI do not offer very precise resolution. Instead, they record from large swaths of brain tissue. With these technologies, we can evaluate whether a large population of cells are more of less activebut not what any individual cell is doing. Its not clear whether neuroscience actually needs to know the functionality of each cell, but its clear that our recording technology provides highly ambiguous information.

The second half of the problem lies with the difficulty with brain stimulation. Non-invasive stimulation technologies (like transcranial magnetic stimulation) can be done pretty easily, but these technologies also lack precise resolution. In this case, even if our recording technologies provide un-ambiguous data, we could not intentionally produce that same activity pattern.

If we could reproducibly induce gay or straight preferences, we would know with real confidence that we had discovered the biological basis of homosexuality. Tangentially, if we had the technical capacity to change a persons sexual orientation, it would open up a pandoras box of ethical dilemmas (should a parent have the right to convert their child?). Fortunately, this horror scenariolike Mike Pences conversion-camp fantasyis well beyond our technical capabilities.

A Bigger Problem; Neurosciences Persistent Fallacy

Perhaps, though, we ought to try a thought experiment. Lets say its a little bit in the future, and a son just announced to his father that he is, in fact, gay. The father decides that he needs some verification, and, as such, the father takes his son to see the local scientist. The scientist explains that long ago, researchers identified the neural correlates to being gay, as described above, using the round-up and scan method. The scientist then tells the father that he can place the son in the scanner, and, after a short while, determine whether his brain has the characteristics that make his brain gay.

Neuroscientists have long hoped that a persons mental state could be inferred based on the findings of a brain scan. What Russell Poldrack and many other neuroscientists have argued, however, is that this approach relies on questionable reasoning. If we understand a persons psychology, the argument goes, we can also identify the underlying neurology. Just throw the person in a brain-scanner, and theres your answer. However, going one step furthertaking that newly discovered neurologyand inferring that same psychology in a different person is something of a logical leap.

X Y does not imply Y X, because sometimes, maybe, Z Y. Also, some Xs are Ys does not imply that all Xs are Ys.

Its pretty simple. Scientists might be able to observe that gay people, on average, have one sort of brain. But not every gay persons brain is going to appear gay. Furthermore, some non-gay people may have brains that appear gay, even if they are not gay. The differences that scientists observe in the brain are based on group averages; they almost never perfectly distinguish between two groups of people, and, in the case of the study linked here, they did not appear to. The concept is called reverse inference. Its both neurosciences greatest ambition, and the origin of its most frustratingly breathless overstatements.

However, enlightened neuroscientists do note that reverse inference is not necessarily wrong, and, at times, it may be useful. Even if we cannot be 100% sure that a particular brain region underlies a particular trait, maybe we can be 95% sure. Oftentimes, the correlations we find with brain imaging research are suggestive. Nevertheless, especially in situations where there is some variability in the neurobiology (which, is basically, every brain scan study), people need to be very cautious in making that final reverse inference.

Conclusion

Neuroscience cannot tell us much about psychology without relying on current psychological measures. In order to conduct research, we have to have some operational definitions. In this caseif we want to identify the neural correlates of being gaywe have to rely on whether people say theyre gay. Self-report is a premise of the argument, which means that science is not well-prepared to transcend self-report. If a person states that he or she is gay, neuroscience is generally not in a position to elaborate.

As a scientist, I believe in the importance of science-advocacy, and I agree with the sentiment that much evil originates from humankinds attempts to define and divide our species into various categories. I also believe that sexuality does not have to be a rigid unchanging quality defined at birth.

However, in this case, we are likely placing solidarity-signaling over neutral scientific reasoning. Confidently asserting the existence of inevitably-gay-brains might make for the ultimate alliance with the LGBTQ community, but it may overstate the confidence of our science. Scientists are allying with the LGBTQ community certainly not because of political identity, no, but because its rational to do, in their viewbecause its scientific to do so.

But some political questions transcend objective reality. Whether climate change is happening is science, whether we should do something about it isnt. Whether or not we believe that a society ought to embrace homosexuality, or a government ought to protect LGBTQ rights, is a moral question, not a scientific one.The underlying scientific reality can inform our position on whether we support gay rights, but its only part of the equation.

Andrew Neff lectures in psychology at Rochester University and runs the blog Neuroscience From Underground.

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When Neuroscience Interjects Itself into Debates on Sexuality - Merion West

The filmgoers didnt flinch at the scene of the dapper man planting a time bomb in the trunk of the convertible, or tense up as the unsuspecting driver and his beautiful blonde companion drove slowly through the town teeming with pedestrians, or jump out of their seats when the bomb exploded in fiery carnage. And they sure as heck werent wowed by the technical artistry of this famous opening shot of Orson Welles 1958 noir masterpiece, Touch of Evil, a single three-minute take that ratchets up the suspense to 11 on a scale of 1 to 10.

In fairness, lab mice arent cineastes. But where the rodents fell short as film critics they more than delivered as portals into the brain. As the mice watched the film clip, scientists eavesdropped on each ones visual cortex. By the end of the study, the textbook understanding of how the brain sees had been as badly damaged as the Touch of Evil convertible, scientistsreportedon Monday.

The new insights into the workings of the visual cortex, they said, could improve technologies as diverse as self-driving cars and brain prostheses to let the blind see.

Neuroscience lets us make better object recognition systems for, say, self-driving cars and artificial intelligence-based diagnostics, said Joel Zylberberg of York University, an expert on machine learning and neuroscience who was not involved in the new research. But computer vision has been hampered by an insufficient understanding of visual processing in the brain. The unprecedented findings in the new study, he said, promise to change that.

The textbook understanding of how the brain sees, starting with streams of photons landing on the retina, reflects research from the 1960s that won two of its pioneers aNobel prizein medicine in 1981. It basically holds that neurons in the primary visual cortex, where the signals go first, respond to edges: vertical edges, horizontal edges, and every edge orientation in between, moving and static. We see a laptop screen because of how its edges abut whats behind it, sidewalks because of where their edges touch the curbs. Higher-order brain systems take these rudimentary perceptions and process them into the perception of a scene or object.

Its been known for more than a decade that this textbook model is partly wrong and largely incomplete, said neurobiologist Saskia de Vries of the Allen Institute for Brain Science, who led the mouse-vision study. To see if she could do better, she and her colleagues showed mice simple gratings (lots of edges), moving gratings,118 photos, and the Touch of Evil opening, recording the resulting electrical activity from hundreds of neurons in six regions of each mouses visual cortex.

Which visual features neurons responded to showed that the textbook model doesnt hold up very well, de Vries said. Only about 10% of the mices visual neurons responded to specific kinds of edges (straight or tilted, horizontal or vertical, sharp or blurry, fat or slender) as per the textbook version of the visual cortex, she and her colleagues reported in Nature Neuroscience. Instead, some responded only to movements of facial muscles, others to several features rather than to a single kind of edge. Yet others, they speculate, might even respond to sounds.

Touch of Evil elicited responses from the greatest number of neurons. That makes sense. In Welles opening scene, the camera zooms in and pans out, it sweeps across the scene, and different people and objects move into and out of the frame, a smorgasbord of imagery that should cover just about everything a visual cortex might need to process. But textbooks say that fewer neurons respond to complex visual scenes than to the simpler, edge-based elements the scenes are made of. The Allen Institute team found the opposite: Static gratings interested the fewest neurons; Welles had a much bigger fan base.

All told, 77% of neurons throughout the mices visual cortex responded to at least one thing the scientists showed them. But in some neighborhoods, only 33% did. The rest seemed to be on strike.

Thats not supposed to happen either. Thats a huge finding, said neuroscientist Bruno Olshausen of the University of California, Berkeley, who hasarguedthat neuroscience understands no more than 20% of how the visual cortex actually operates. Every visual neuron supposedly responds tosomekind of edge, so what are these silent neurons doing? Olshausen asked. Assuming the finding isnt an artifact, thats a huge population of [visual] neurons that arent doing vision. This should be a wake up call to everyone in the field. Something is dramatically wrong with the standard model.

The surprise finding, he added, makes this a tour de force and a first in neuroscience, to systematically characterize such a large population of neurons across different layers, areas and using different stimuli. The data will be invaluable to theorists and modelers for years to come.

It could be that the scientists didnt show the mice images with the particular feature that these unresponsive visual neurons notice. But that seems unlikely, given the diversity of images: butterflies, leopards, fences, mountains, trees, leaves, rocks, sidewalks, windows, staircases, pencils, and more. Instead, de Vries said, I think its a reflection that other things are going on in the visual cortex, like visual neurons processing sound or something else non-visual.

Since machine-vision developers take their cues from how brains see, the Allen Institute results, if confirmed, carry an important message, Yorks Zylberberg said. It shows that there isnt a mess of [undifferentiated neurons] doing all the same thing, which is what we put into our systems now. Instead, theres at least 10 different types of visual neurons that respond to specific aspects of the visual worlda complexity that computerized object-recognition systems might profitably emulate.

As for the scientists choice of flicks, we picked Touch of Evil because we were looking for a movie clip that had a lot of diverse motion without camera cuts, de Vries said.

Republished with permission from STAT. This article originally appeared on December 16 2019

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What Mice Watching Orson Welles's Touch of Evil Can Teach Scientists about Vision - Scientific American