It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Wednesday, June 07, 2023
Leading plant science journal publishes a special issue on key discoveries in plant pathology
IMAGE: JOURNAL COVER OF THE KEY DISCOVERIES ISSUE OF PHYTOPATHOLOGY, FEATURING HAIRY ROOT FORMATION FROM WOUND SITES ON THE STEM OF A KALANCHOE DAIGREMONTIANA PLANT AFTER INFECTION BY AGROBACTERIUM RHIZOGENES STRAIN LBA9402 (HOOYKAAS). PHOTO CREDIT: PAUL AND MARJOLEIN HOOYKAASview more
CREDIT: THE AMERICAN PHYTOPATHOLOGICAL SOCIETY; PAUL AND MARJOLEIN HOOYKAAS
In just 7 years, the Irish Potato Famine caused approximately one million people to starve to death and forced another estimated million to flee Ireland as refugees. A mold called Phytophthora infestans infected Ireland’s potato crop, a staple food, and spread rapidly throughout the island. The seemingly tiny fungus destroyed roughly 75% of potato crops over the duration of the great hunger. This catastrophic famine, along with several others in various parts of the world throughout history, highlighted the critical need for the study of plant diseases.
Decades of groundbreaking discoveries about plant diseases ensued in the following century. Building from these discoveries, plant pathology continues to play a vital role in safeguarding plant health, food security, and food safety worldwide. The flagship journal of the American Phytopathological Society, Phytopathology, recently published a special issue—the first of a new series—examining how several key discoveries in plant pathology during the past 50 years have impacted the life sciences and plant disease management. This issue contains articles by top experts in various scientific fields, who review the discovery process, recent progress, and impact of these discoveries, while pointing out future directions for new discoveries in fundamental and applied plant pathology.
The key discoveries discussed in the first installment of this journal series include the Agrobacterium Ti plasmid and its mechanism in T-DNA transfer; bacterial ice nucleation; cloning of resistance genes; discovery of viroids; effectors and their mechanisms; pattern-triggered immunity and effector-triggered immunity; RNA interference and gene silencing; structure and function of R genes; transcription activator-like effectors; type-III secretion system and hrp/hrc; the deployment and management of host resistance genes; the application of disease models and forecasting systems; the introduction of modern systemic fungicides and host resistance inducers, along with a better understanding of fungicide resistance mechanisms and management; and the utilization of biological controls and suppressive soils, including the implementation of methyl-bromide alternatives.
These articles, both retrospective and forward-thinking, can significantly benefit researchers and students in plant pathology (plus related fields) and applied plant disease managers. Additionally, the Key Discoveries in Plant Pathology series will continue to benefit these individuals as new issues addressing other topics are published. Phytopathology Editor-in-Chief Nian Wang and past Editor-in-Chief Harald Scherm remark, “The special issue includes many key discoveries in plant pathology with tremendous importance. To allow coverage of important discoveries that were not reviewed due to space and time limitations in the present issue, the Key Discoveries series will continue as special issues or as individual articles. Colleagues are encouraged to submit review articles on key discoveries in plant pathology in the past 50 years.” In addition, the journal series will feature articles on the impact of advances in fields such as climate science, remote sensing, artificial intelligence, imaging technology, and synthetic biology on the discipline of plant pathology.
The aim of this issue and further issues is to explore how plant pathology has helped, and continues to help, protect plant and environmental health in the face of population growth and climate change.
Reflecting the crucial role for open access in making relevant research available to readers outside of academia, Technology and Sustainable Development focuses on many of the practical challenges facing our governments and societies today.
The potential of technology to both solve and exacerbate pressing global issues, including gender inequality, the climate crisis, mistreatment of minorities, and the unequal distribution of power, is addressed by a range of experts in the book edited by Henrik Skaug Sætra.
The book explores the implications of new technologies, such as artificial intelligence, social media and big data, as well as considering the need for greater social and political control of such developments.
James Watson, Open Access Books Lead at Taylor & Francis, said: “Our 1,500th OA book, which has human-centered science at its heart, demonstrates why open access publishing is so important. At a time of unprecedented technological change, Technology and Sustainable Development is a vital resource not just for researchers with access to university libraries but also for policymakers, politicians and all those tackling the social, economic and environmental challenges faced by our societies”.
Taylor & Francis marks 10 years of open access book publishing in 2023. With over 1,500 fully OA titles in its portfolio, combined with thousands of individual open chapters, Taylor & Francis is one of the leading open access book publishers. Its OA books program enables authors and their funders to publish open access single- or co-authored books, edited collections and individual chapters. Upon publication, OA content is made available in digital format to read and download freely under a Creative Commons license.
IMAGE: ENVIRONMENTAL RESEARCH: FOOD SYSTEMS LOGOview more
CREDIT: IOP PUBLISHING
IOP Publishing (IOPP) is expanding its open access (OA) Environmental Research portfolio to address the urgent need for sustainable food solutions globally. Environmental Research: Food Systems, which supports the United Nation’s Sustainability Development Goals (SDGs), is an interdisciplinary forum for researchers working to achieve sustainable global food security.
Scientific innovations are key to transforming the global food system. Efficient and effective food supply enables the world to achieve progress on all 17 of the SDGs, from eliminating poverty and hunger through to lowering emissions of climate-warming gases. According to recent stats from market insights provider, The Lens, research outputs related to food systems have increased by more than 200% and citations have more than doubled in the last 10 years.
Nathan Mueller, newly appointed Editor in Chief of Environmental Research: Food Systems and Assistant Professor at Colorado State University, says: “The health and well-being of people and the planet requires environmentally, socially, and economically sustainable food systems. As the world faces a changing climate, a growing population, and widespread food insecurity, the need for innovative transdisciplinary food systems research is greater than ever. From production to consumption and local to global, Environmental Research: Food Systems is a home for rigorous, open access science that can promote innovation, inform policy and practice, and foster transformative change for a sustainable and secure future.”
Dr Tim Smith, Head of Portfolio Development at IOP Publishing says: “Science plays a crucial role in addressing the cracks in the global food system. Environmental Research: Food Systems has been launched to meet the need for an open access research platform that addresses the future risks, security and adaption of our food systems worldwide at a time when the need for sustainable food solutions has never been more pressing.”
IOP Publishing will waive all OA article publication charges for articles submitted to the journal before 2025. In the spirit of transparency and reproducibility, authors publishing in the journal are encouraged to share data and code where appropriate for the benefit of the research community. Authors also have the option to submit their papers for double anonymous and transparent peer review.
Environmental Research: Food Systems is the latest addition to IOPP’s expanding Environmental Research Series which is now made up of eight OA journals.
Investigating the placenta: Discovery from Stowers Scientists shows why this often-overlooked organ should be given more attention
IMAGE: GRAPHICAL SCHEMATIC OF FULLY DEVELOPED MOUSE PLACENTA AT 14.5 DAYS POST CONCEPTION (TOP). FLUORESCENT IMAGES OF VARIOUS PLACENTAL CELL TYPES ILLUSTRATING MULTIPLE GENOME COPIES (WHITE DOTS) WITHIN CELLS (BOTTOM).view more
CREDIT: STOWERS INSTITUTE FOR MEDICAL RESEARCH
KANSAS CITY, MO—June 7, 2023—The placenta, critical for healthy embryo development, is a multi- purpose organ with a precise lifespan—the length of a pregnancy. New research from the Stowers Institute for Medical Research suggests that further exploration of the placenta’s roles and capabilities may one day lead to insights for positive pregnancy outcomes.
The study published in Development on June 6, 2023, focuses on a unique property of many cells comprising the placenta that explains how these cells perform essential functional and physical roles to support a developing embryo.
“Following birth, the placenta is often tossed in the medical wastebin,” explained Stowers Investigator Jennifer Gerton, Ph.D. “This makes it the most overlooked, undervalued, and understudied organ in reproductive science.”
Placental cells are very large and have high metabolic activity, enabling them to serve as a physical barrier and to facilitate nutrient and hormone exchange between mom and baby. New insights from research performed on mice led by former Postdoctoral Researcher Vijay Singh, Ph.D., from the Gerton Lab, could help researchers and clinicians understand in greater detail how the placenta supports healthy human pregnancies.
“We really care about conditions like birth defects and premature birth, but we are often solely focused on the baby,” said Gerton. “Many of these problems impacting the fetus originate with the placenta, and until we understand it more, we are missing vital information.”
Normally, when cells divide, their chromosomes are first duplicated and then split between the two new cells. The distinct feature of placental cells identified here originates from a modified cell cycle, where following replication of chromosomes, the cell does not divide, and instead retains an entire extra chromosomal set. This cycle can occur repeatedly so that placental cells grow to gigantic proportions with hundreds of chromosome copies, a characteristic called polyploidy.
While certain placental cells were already known to be polyploid, a surprising aspect revealed in the current study was that many cell types in a mouse placenta have this feature. “When each cell has multiple copies of the genome, that makes them very robust. The large size also helps create a barrier between the developing embryo and the mom,” said Gerton. “The placenta may be the most polyploid organ in a pregnant female mouse, but more research into polyploidy is warranted.”
Polyploid placental cells are essential for normal development of the placenta and a healthy placenta is vital for embryonic development and a successful pregnancy. Problems with the placenta are linked to preterm birth, restricted fetal growth, preeclampsia, and even fetal death. The placenta performs various functions including nutrient transport from mom to fetus, hormone and blood cell production, and protecting the developing embryo from the mother’s immune system which would otherwise reject it.
The study revealed the modified cell cycle controlling polyploidy is governed by a regulatory gene called Myc which is found in organisms as diverse as fruit flies, mice, and humans. In addition, Myc supports DNA replication and prevents premature cellular aging of the placenta.
The team made a genetic mutation in Myc that caused cells to fail to achieve polyploidy in mouse placenta. “Based on the outcome, we speculate that if human placental cells do not achieve polyploidy, for instance due to environmental toxins like alcohol or cigarette smoke, the placenta will not be able to do its jobs and support a healthy pregnancy,” said Gerton.
“Many people donate organs for scientific research,” said Singh. “If more parents are aware of the benefit of studying human placentas, perhaps they would be willing to donate theirs to push research forward.”
“We might learn a lot if more attention is paid to the placenta which can be the cause of disease in a baby,” said Gerton. “I feel like generally as scientists and as a society, we’re simply not giving the placenta its due consideration.”
Read more here on Development’s Research highlight.
Additional authors include Huzaifa Hassan, Fengyan Deng, Ph.D., Dai Tsushiya, Ph.D., Sean McKinney, Ph.D., and Kevin Ferro, Ph.D.
Funding for this work was provided by the Stowers Institute for Medical Research.
About the Stowers Institute for Medical Research
Founded in 1994 through the generosity of Jim Stowers, founder of American Century Investments, and his wife, Virginia, the Stowers Institute for Medical Research is a non-profit, biomedical research organization with a focus on foundational research. Its mission is to expand our understanding of the secrets of life and improve life’s quality through innovative approaches to the causes, treatment, and prevention of diseases.
The Institute consists of 20 independent research programs. Of the approximately 500 members, over 370 are scientific staff that include principal investigators, technology center directors, postdoctoral scientists, graduate students, and technical support staff. Learn more about the Institute at www.stowers.org and about its graduate program at www.stowers.org/gradschool.
Microscopy image of trophoblast giant cells in a mouse placenta stained to visualize DNA and filament proteins. Image captured by and in memory of Pablo Guzmán Palma.
Mouse trophoblast giant cell within placenta.
Mouse trophoblast giant cells (green) at nine days post conception for normal mice (top) and for mice with Myc mutation (bottom) that disrupts polyploidy.
ANN & ROBERT H. LURIE CHILDREN'S HOSPITAL OF CHICAGO
More than three in five children (63 percent) enrolled in Medicaid do not receive mental health services within six months after a firearm injury, according to a new study published in the journal Pediatrics.
In the United States, 11,258 youth experienced nonfatal firearm injuries in 2020. Children who survive firearm injuries are at increased risk for adverse mental health outcomes, such as newly diagnosed trauma-related disorders, substance use and disruptive disorders. In addition to these disorders, the study found that after injury, the percentage of children diagnosed with bipolar disorder, schizophrenia spectrum disorders, and suicidal ideation/self-injury nearly doubled.
“In our study, we found that while too many children did not receive mental healthcare follow-up, children with a new mental health diagnosis identified during the firearm injury encounter had over twice the odds of timely connection to outpatient mental healthcare,” said lead author Jennifer Hoffmann, MD, MS, Emergency Medicine physician at Ann & Robert H. Lurie Children’s Hospital of Chicago and Assistant Professor of Pediatrics at Northwestern University Feinberg School of Medicine. “This shows that after a firearm injury, mental health screening and referral for youth at high risk are essential, as well as required by the 2022 American College of Surgeons standards for pediatric trauma centers. This best practice still needs wider implementation.”
The study also detected inequities in mental healthcare access after a firearm injury, with Black youth less likely to have any mental health follow-up than White youth.
“Mechanisms underlying these inequities may include stigma and costs related to accessing care, limited diversity in the mental health workforce, and shortages of mental health professionals in areas where Black children live,” said Dr. Hoffmann. “Attention is needed to address barriers at the individual, health system, and societal levels that may prevent Black youth from accessing mental health services.”
For the study, Dr. Hoffmann and colleagues examined Medicaid data of children aged 5-17 years with a nonfatal firearm injury, living in 11 geographically dispersed states from 2010-2018. They identified 2,613 children with firearm injuries. The objective was to analyze how timing of the first outpatient mental health visit after firearm injury varies by sociodemographic and clinical characteristics. They found that the first outpatient mental health visit after injury occurred sooner among children with prior mental health service use.
“For children without prior mental health service use, greater efforts are needed to connect them to mental health providers,” said Dr. Hoffmann. “To improve outcomes, it is important to prioritize early detection of mental health needs, equitable access to mental healthcare and timeliness of care.”
Dr. Hoffmann is the Children's Research Fund Junior Board Research Scholar.
Research at Ann & Robert H. Lurie Children’s Hospital of Chicago is conducted through Stanley Manne Children’s Research Institute. The Manne Research Institute is focused on improving child health, transforming pediatric medicine and ensuring healthier futures through the relentless pursuit of knowledge. Lurie Children’s is a nonprofit organization committed to providing access to exceptional care for every child. It is ranked as one of the nation’s top children’s hospitals by U.S. News & World Report. Lurie Children’s is the pediatric training ground for Northwestern University Feinberg School of Medicine. Emergency medicine-focused research at Lurie Children’s is conducted through the Grainger Research Program in Pediatric Emergency Medicine.
IMAGE: PARMINDER RAINA, PROFESSOR, DEPARTMENT OF HEALTH RESEARCH METHODS, EVIDENCE, AND IMPACT AT MCMASTER UNIVERSITY, LEAD PRINCIPAL INVESTIGATOR OF THE CANADIAN LONGITUDINAL STUDY ON AGING AND THE STUDY’S SENIOR AUTHOR.view more
CREDIT: MCMASTER UNIVERSITY
Disadvantaged neighbourhoods and depression symptoms associated with premature aging
Hamilton, ON (June 5, 2023) - Feeling depressed and living in a deprived urban neighbourhood could be making you age faster, according to a new study led by researchers at McMaster University.
The findings, published June 5 in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences,showed that living in urban environments marked by material and social inequities, and having depression symptoms, were independently associated with premature biological aging, even after accounting for individual-level health and behavioural risk factors, such as chronic conditions and poor health behaviours.
Parminder Raina, a professor in the Department of Health Research Methods, Evidence, and Impact at McMaster University, led the research team, which included investigators from the Netherlands, Norway and Switzerland.
“Our study used two DNA methylation-based estimators, known as epigenetic clocks, to examine aging at the cellular level and estimate the difference between chronological age and biological age,” said Divya Joshi, the study’s first author and a research associate in the Department of Health Research Methods, Evidence, and Impact at McMaster.
“Our findings showed that neighbourhood deprivation and depressive symptoms were positively associated with acceleration of the epigenetic age estimated using the DNAm GrimAge clock. This adds to the growing body of evidence that living in urban areas with higher levels of neighbourhood deprivation and having depression symptoms are both associated with premature biological aging.”
Depressive symptoms in the study were measured using a 10-item standardized depression scale. The researchers found an acceleration in the risk of death by one month for every point increase on the depressive symptom score. They theorized that emotional distress caused by depression may result in more biological wear and tear and dysregulation of physiological systems, which in turn could lead to premature aging.
The researchers assessed neighbourhood material and social deprivation using two indices that were developed by the Canadian Urban Environmental Health Research Consortium (CANUE) based on 2011 census.
Social deprivation reflects the presence of fewer social resources in the family and community, and material deprivation is an indicator of people’s inability to access goods and conveniences of modern life, such as adequate housing, nutritious food, a car, high-speed internet, or a neighbourhood with recreational facilities.
The researchers found an increase in the risk of death by almost one year for those exposed to greater neighbourhood deprivation compared to lower neighbourhood deprivation.
The study did not find that neighbourhood deprivation amplified the effect of depressive symptoms on epigenetic age acceleration.
“Our results showed that the effect of neighbourhood deprivation on epigenetic age acceleration was similar regardless of depression symptoms, suggesting that depression influences epigenetic age acceleration through mechanisms unrelated to neighbourhood deprivation,” Joshi said.
The research examined epigenetic data from 1,445 participants enrolled in the Canadian Longitudinal Study on Aging (CLSA), a research platform following more than 50,000 participants who were between the ages of 45 to 85 when recruited.
“Longitudinal studies, like the CLSA, are important to confirm associations like those found in this study,” said Raina, the study’s senior author and lead principal investigator of the CLSA.
“By following the same group of participants for 20 years, we will be able to determine whether epigenetic changes are stable or reversible over time. We will also gain insight into the mechanisms that are leading to accelerated epigenetic aging.”
Support for the CLSA is provided by the Government of Canada through the Canadian Institutes of Health Research and the Canada Foundation for Innovation. Additional support for this study was provided by the European Union Horizon 2020 Programme.
Association of Neighborhood Deprivation and Depressive Symptoms With Epigenetic Age Acceleration: Evidence From the Canadian Longitudinal Study on Aging
ARTICLE PUBLICATION DATE
5-Jun-2023
Neurotic people are more likely to suffer from mood swings
Study by Leipzig University on the connection between neuroticism and emotional experiences
“Previous studies are in agreement that neurotic people experience stronger negative emotions in everyday life. Because of new, contradictory studies, there has been disagreement about whether this is also associated with increased variability in emotional experiences, i.e. mood swings,” says the study’s first author, Nina Mader from the Wilhelm Wundt Institute of Psychology at Leipzig University. Personality psychologists at Leipzig University have developed a new approach to modelling data that solves previous methodological problems. “We use an approach from Bayesian statistics that allows additional flexibility in data modelling. We first successfully tested this approach in simulations and then re-examined 13 longitudinal data sets. The results suggest that neurotic people do indeed experience greater variability in negative emotions,” explains Mader. A total of 2,518 people were asked about their emotions.
Neuroticism is a personality trait. Personality traits are relatively stable and consistent across situations over time. They encompass both our experiences and our behaviour, including how we think (cognition) and how we feel (affect). People have different personalities and therefore different levels of neuroticism. “So there is not a black-and-white division between neurotic and non-neurotic people, but rather a dimensional continuum with many shades of grey,” says the psychologist.
People with high neuroticism scores not only experience negative emotions more strongly, but also more often than people with average or below-average scores. They are more often self-critical, react more poorly to external criticism, and are more likely to experience feelings of ‘not being good enough’. Studies have shown that neuroticism scores are highest in late adolescence and then decline and stabilise in adulthood. In addition, women and people with a low socio-economic status have higher neuroticism scores than other people.
Since the 1990s, personality psychologists have been interested in whether and how personality influences our emotional experiences. Several studies have assessed the personalities of large samples and observed emotional experiences over time. For example, respondents were asked several times a day how sad, angry or bored they felt on a scale of 1 to 7. This revealed a clear connection between neuroticism and the experience of negative emotions. “While negative emotions occur very rarely in the everyday lives of people with low neuroticism scores, people with high neuroticism scores report significantly more negative emotions in everyday life,” explains Mader. This is typically associated with a disproportionate reaction to triggering circumstances. For example, a minor difference of opinion could cause great anger in the latter, or even the mere thought that the train might be very crowded today could cause intense stress and worry.
Original title of the publication in PNAS:
“Emotional (in)stability: Neuroticism is associated with increased variability in negative emotion after all”, doi.org/10.1073/pnas.221215412
IMAGE: APPROXIMATELY ONE IN FIVE PEOPLE IN FINLAND REPORTED THEY EXPERIENCED SYMPTOMS RELATED TO INDOOR AIR. SOME OF THEM DID NOT THINK THE SYMPTOMS AFFECTED THEIR FUNCTIONAL CAPACITY AT ALL, BUT A SMALL PART FOUND THAT THE SYMPTOMS CAUSED SIGNIFICANT FUNCTIONAL IMPAIRMENT.view more
CREDIT: FINNISH INSTITUTE FOR HEALTH AND WELFARE (THL)
Approximately one in five people in Finland reported they experienced symptoms related to indoor air. Some of them did not think the symptoms affected their functional capacity at all, but a small part found that the symptoms caused significant functional impairment.
This is revealed by a study conducted by the Finnish Institute for Health and Welfare (THL), the Finnish Institute of Occupational Health and the University of Helsinki, published in the Journal of Occupational and Environmental Medicine.
Approximately two in three people suffering from symptoms experienced at most mild functional impairment due to symptoms. The more severe the respondents found the functional impairment due to symptoms, the more common were also many diagnosed illnesses, the person’s perception of poor health, diverse symptoms across the body and sensitivity to different environmental factors.
”Persons suffering from difficult symptoms and severe functional impairment make up a small part of those getting symptoms from indoor air. They need special support because they have also accumulated many other factors impairing their functional capacity,” says Senior Specialist Sanna Selinheimo from the Finnish Institute of Occupational Health.
The differences in functional capacity and the prevalence of other health problems in symptomatic persons should be taken into account better in activities that support a symptomatic person’s rehabilitation and ability to cope with everyday life and work.
“The results support earlier research results in that, in addition to indoor air impurities, there are also many other factors behind the severity of symptoms related to indoor air,” says Professor Juha Pekkanen from THL and the University of Helsinki.
The study is based on the National Indoor Air Survey 2018, to which 4,997 Finnish-speaking people aged between 25 and 64 years and living in Finland (excl. Åland) were selected in a random sample. Of them, 1,797 responded to the survey.
The more severe the respondents found the functional impairment due to symptoms, the more common were also many diagnosed illnesses, the person’s perception of poor health, diverse symptoms across the body and sensitivity to different environmental factors.
CREDIT
Finnish Institute for Health and Welfare (THL)
JOURNAL
Journal of Occupational and Environmental Medicine
IMAGE: PAVLOVIAN VERSUS OPERANT CONDITIONING EXPERIMENTview more
CREDIT: NETHERLANDS INSTITUTE FOR NEUROSCIENCE
A new study from the Netherlands Institute for Neuroscience brings together two schools of thought on the function of the neurotransmitter dopamine: one saying that dopamine provides a learning signal, the other saying that dopamine drives motivation. ‘But it is probably both’, says Ingo Willuhn.
It is well-known that the dopamine system is implicated in signaling reward-related information as well as in actions that generate rewarding outcomes. This can be investigated using either Pavlovian and operant conditioning experiments. Pavlovian conditioning describes how your brain makes an association between two situations or stimuli that previously seemed unrelated. A famous example is Pavlov’s experiment, where a dog heard a sound before receiving food. After several such pairings of the sound with food delivery, the sound alone began to cause the dog to salivate. Operant conditioning, or instrumental learning, differs from this in that the behavior of an individual is important to earn a food reward. Meaning that the individual after hearing a sound, has to perform a so-called operant action to receive the reward. In animal experiments, such a operant response is often the pressing of a lever.
Dopamine measurements in nucleus accumbens
In the final PhD paper of Jessica Goedhoop in collaboration with Tara Arbab and Ingo Willuhn from the Netherlands Institute for Neuroscience, they take a closer look at the role of dopamine signaling in learning and motivation. The team directly compared the two conditioning paradigms: male rats underwent either Pavlovian or operant conditioning while dopamine release was measured in the nucleus accumbens, a brain region central for processing this information. During the experiments a cue light was illuminated for a duration of 5 seconds. For the Pavlovian group, a food pellet was delivered into the reward magazine directly after the cue light turned off. For the operant conditioning group, turning off the cue light was followed by extension of the lever below the cue light into the operant box. The lever was retracted after one lever press, which immediately resulted in the delivery of one food pellet reward into the food magazine. If there was no lever press within 5 seconds after lever extension, the lever was retracted and no reward was delivered.
Sustained dopamine release in operant conditioning
Rats in both groups released the same quantity of dopamine at the onset of the reward-predictive cue. However, only the operant-conditioning group showed a subsequent, sustained plateau in dopamine concentration throughout the entire 5-second cue presentation (throughout cue presentation and before lever press). This dopamine sustainment was observed reliably and consistently throughout systematic manipulation of experimental parameters and behavioral training. Therefore, the researchers believe that sustained dopamine levels may be an intermediate between learning and action, conceptually related to the motivation to generate a reward-achieving action.
Ingo Willuhn: ‘There have been a lot of studies on dopamine. We have a decent idea of when dopamine is released in the brain, but there is still lots of discussion on what the precise variables are that determine such dopamine signaling. Essentially discussion on what dopamine “means”. To investigate this, scientists usually perform either Pavlovian or operant conditioning experiments. But they test slightly different things. Both have to do with learning an association between a neutral stimulus and a reward. But operant conditioning requires the motivation to perform an action in addition to that (to earn the reward). Therefore, we compared the two types of conditioning in the same experiment.’
Adding a piece to the puzzle
‘Our results bring together the two camps of scientists that often battle with each other: one says that dopamine is a so-called reward-prediction error signal, meaning that dopamine is released when something better than expected happens, and is suppressed when something worse than expected happens. It is a learning (or teaching) signal. The other camp says that this is not true. They say that dopamine has something to do with motivation. Increased dopamine release will invigorate the subjects and they work harder to get the reward. There have been a few attempts in the past to bring these two camps together, but there is still need for more knowledge on the subject.’
‘What we saw in our study is that only in the operant-learning task dopamine levels stayed high. It seems that the motivation is encoded in this plateau. Reward prediction is the initial dopamine peak, but how much the signal stays up, reflects motivation. Thus, our paper suggests that there is a possibility that dopamine is involved in both, learning and motivation. The next steps will be to get more details out of this. We need to replicate the experiments and make them more sophisticated. The more sophisticated you make it, the more precise our predictions have to be. We are going to build on it and see whether it still holds up.’
Implications
‘Dopamine is not only involved in everyday life but also in disorders such as addiction, Parkinson’s disease, and schizophrenia. Because of the two camps existing, there is disagreement about what happens exactly. For example, some researchers say that when addicts take drugs dopamine release increases and as a consequence all the environmental cues become more meaningful. Addicts learn that these cues are associated with the drug and they take more and more drug, because they are constantly reminded of the drug everywhere. In this view, addiction is misguided learning. Other researchers would say that motivation to take the drug intensifies with more frequent drug intake, because the drug elevates dopamine release. This study indicates that it may be both. Depending on the precise timing, both systems could be the driver, and both could be involved.’
‘This is also relevant for the clinic. Prescribed drugs can influence both learning and motivation systems at the same time: and then it can get messy. If you give schizophrenic patients classic antipsychotic medication, they become slow and cannot act much because their motivation system is down. Parkinson’s patients take pro-dopamine drugs essentially because they lost their dopamine, but some patients start to gamble because their dopamine system is on overdrive suddenly. We cannot influence learning and motivation components separately. As soon as you give a drug it is going to hit all of it, so it is good to keep that in mind.’
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