Pattern separation is the means by which the brain discriminates similar experiences. It enables retrieval of individuated memories without confusing them with other memories. It is the reason one remembers where one parked the car today and does not mix it up with where one parked it previously. Adult neurogenesis refers to the ongoing production of neurons in the mature brain. One of the likely roles of adult neurogenesis in the hippocampus is facilitating pattern separation. Induced reduction of adult neurogenesis in non-human animals is associated with depression- and anxiety-like behaviors. One possible explanation is that reduced neurogenesis leads to reduced pattern separation, further leading to overgeneralization of threat situations. Instead of perceiving threats where it should, the animal risks perceiving threats everywhere. Emotional resilience is the ability to recover from adversity with a minimum of lingering negative effects such as depression or anxiety. This thesis investigates whether pattern separation in the human hippocampus supports emotional resilience. I performed a systematic review of studies that used the Mnemonic Similarity Task – a memory task commonly used to measure human pattern separation – to investigate the relationship between pattern separation and anxiety. The results are inconclusive but suggest a possible interaction effect whereby pattern separation and high-arousal states like stress predict anxiety. Together with the evidence from the non-human animal studies, this suggests that reduced pattern separation as caused by reduced neurogenesis could make one vulnerable to developing anxiety disorders.

Meditation has in recent decades received attention mainly for its health benefits in western society, not least in the field of neuroscience. Researchers are frequently exploring the link between plasticity in the brain, and the practice of meditation. This systematic review aims to investigate the underlying functional and structural differences in brain mechanisms between long-term meditators and non-meditators, involving different meditation forms. A total of seven peer-reviewed articles were included after being screened for, and meeting inclusion criteria. Final outcomes demonstrated differences between meditators and non-meditators in both functional and structural measures. Some brain regions where changes were identified in meditators included higher-order cognitive areas (i.e., frontal and temporal brain regions). These brain regions are known to be involved in emotional, attentional and memory processing. Reduced connectivity within the default mode network (DMN) is known to be associated with meditation, which was supported in two of the studies. Furthermore, larger gray matter density was found in autonomous control centers (i.e., the brainstem), and larger callosal thickness in meditators. Based on the findings, the practice of long-term meditation appears to be linked with functional and structural changes in various regions of the brain. The findings give insight into the underlying neural correlates and brain plasticity in meditators compared to non-meditators. Nevertheless, future research is necessary for understanding the long-term effects of various meditation forms.

Much work has been done in the neuroscience of reward processing, such as; mapping brain areas, key neurotransmitters, and connectivity patterns related to different aspects of reward-related behavior. There are a lot of suggested behavioral and neural sex differences in reward processing, primarily based on animal studies of reward behavior. This review aimed to systematically review publications on human neurofunctional sex differences in reward processing, and provide a more stable footing for future research in the field. Two searches through Web of Science and Scopus for publications that combined neuroimaging with behavioral tasks for examining functional sex differences in neural reward processing. The searches produced nine studies (n=9) that were included after the screening process. There are significant differences between males and females in reward processing, specifically in the striatum, orbitofrontal cortex, prefrontal cortex, nucleus accumbens, and insula. However, the full extent of these differences, and the underlying causes, are still not clear. There is a lack of control for important confounding factors in the present field of sex differences in reward processing. Future research in this field has to consider all of the underlying factors that cause men and women to differ, such as the impact of gonadal hormone fluctuations and societal pressures. If these factors were taken into account, data of higher validity and generalizability could have been produced.

Rumination, or extensive mind wandering defines one of the key cognitive symptoms of major depressive disorder (MDD). Several symptoms included in the psychiatric disorder have been associated with altered connectivity within the large-scaled system default mode network (DMN). Although it’s well-known that antidepressant treatment, such as selective serotonin reuptake inhibitor (SSRI) and serotonin norepinephrine reuptake inhibitor (SNRI) tend to positively affect symptoms and alterations of MDD, results are inconsistent regarding DMN connectivity pre-and-post treatment. This systematic review aims to compile findings from studies investigating DMN connectivity in MDD patients’ pre-and post SSRI and SNRItreatment, and to find possible correlations with symptomatic improvements. Five articles were included for further analysis after the literature search in MEDLINE ESBSCO and Scopus. Main findings are in alignment with previous research and suggest both hypo-and hyper DMN connectivity at baseline in MDD patients, and connectivity patterns significantly similar to healthy controls following antidepressant treatment. Future research might consider placebo controlled trials for more diverse, and quantified results, and also consider further investigation on both first-line treatments and other promising antidepressants.

The flow state is a subjective experience that most people can relate to. It represents an optimal balance between skills and difficulty and is the state that people often refer to when performing their best, with phrases like: “I was in the zone” or “I was in the bubble”. The flow state has mainly been studied through its psychological and behavioral components; it is not until lately the neuroscientific aspects have been investigated. This review attempts to go through the existing literature and find potential neural signatures of the flow state. The studies indicate that flow is related to activity in the dorsolateral prefrontal cortex and putamen, but the findings are too divided to reach a conclusion.

The basal ganglia form an important structure centrally placed in the brain. They receive input from motor, associative and limbic areas, and produce output mainly to the thalamus and the brain stem. The basal ganglia have been implied in cognitive and motor functions. One way to understand the basal ganglia is to take a look at the diseases that affect them. Both Parkinson's disease and Huntington's disease with their motor problems are results of malfunctioning basal ganglia. There are also indications that these diseases affect cognitive functions. Drug addiction is another example that involves this structure, which is also important for motivation and selection of behaviour. In this licentiate thesis I am laying the groundwork for a detailed model of the striatum, which is the input stage of the basal ganglia. The striatum receives glutamatergic input from the cortex and thalamus, as well as dopaminergic input from substantia nigra. The majority of the neurons in the striatum are medium spiny (MS) projection neurons that project mainly to globus pallidus but also to other neurons in the striatum and to both dopamine producing and GABAergic neurons in substantia nigra. In addition to the MS neurons there are fast spiking (FS) interneurons that are in a position to regulate the firing of the MS neurons. These FS neurons are few, but connected into large networks through electrical synapses that could synchronise their effect. By forming strong inhibitory synapses on the MS neurons the FS neurons have a powerful influence on the striatal output. The inhibitory output of the basal ganglia on the thalamus is believed to keep prepared motor commands on hold, but once one of them is disinhibited, then the selected motor command is executed. This disinhibition is initiated in the striatum by the MS neurons. Both MS and FS neurons are active during so called up-states, which are periods of elevated cortical input to striatum. Here I have studied the FS neurons and their ability to detect such up-states. This is important because FS neurons can delay spikes in MS neurons and the time between up-state onset and the first spike in the MS neurons is correlated with the amount of calcium entering the MS neuron, which in turn might have implications for plasticity and learning of new behaviours. The effect of different combinations of electrical couplings between two FS neurons has been tested, where the location, number and strength of these gap junctions have been varied. I studied both the ability of the FS neurons to fire action potentials during the up-state, and the synchronisation between neighbouring FS neurons due to electrical coupling. I found that both proximal and distal gap junctions synchronised the firing, but the distal gap junctions did not have the same temporal precision. The ability of the FS neurons to detect an up-state was affected by whether the neighbouring FS neuron also received up-state input or not. This effect was more pronounced for distal gap junctions than proximal ones, due to a stronger shunting effect of distal gap junctions when the dendrites were synaptically activated. We have also performed initial stochastic simulations of the Ca2+-calmodulin-dependent protein kinase II (CaMKII). The purpose here is to build the knowledge as well as the tools necessary for biochemical simulations of intracellular processes that are important for plasticity in the MS neurons. The simulated biochemical pathways will then be integrated into an existing model of a full MS neuron. Another venue to explore is to build striatal network models consisting of MS and FS neurons and using experimental data of the striatal microcircuitry. With these different approaches we will improve our understanding of striatal information processing. / QC 20101116

Sensory processing sensitivity is an innate temperament trait characterized by deeper cognitive processing of stimuli, increased empathy and emotionality, ease of overstimulation, and heightened awareness of subtileties in the environment. This systematic review aims to review the literature that has investigated the neural correlates of sensory processing sensitivity. A systematic search was conducted in Web of Science and Scopus resulting in seven studies included in systematic review. Five studies are functional magnetic resonance imaging studies, one magnetic resonance imaging study and one near-infrared spectroscopy study. Results show that sensory processing sensitivity is associated with enhanced activation of neural regions involved in higher order visual processing, attention, awareness, memory, emotion processing, action planning and information integration (e.g., insula, precuneus, IFG, PFC, claustrum, amygdala, and hippocampus). An increased understanding of this temperament trait is essential as it is an important factor for mental health and well-being.

The COVID-19 pandemic left no one unaffected as it spread across the world and changed the lives of billions of people. The pandemic has not only resulted in physical sickness and death, but also increased mental health issues due to fear, uncertainty, and social isolation. This review aimed to investigate whether mindfulness interventions can decrease symptoms of mental illness, such as depression, anxiety, stress, and burnout, and increase symptoms of mental well-being, such as psychological well-being, during the pandemic. All studies included in this thesis used different mindfulness interventions and different self-report measures to evaluate various mental health aspects, such as psychological flexibility, tolerance of uncertainty, empathy, self-compassion, and more. Statistically significant improvements in mental health were observed across all studies and is further supported by existing literature on mental health and mindfulness meditation and interventions.

Som känt sedan tidigare är känsloigenkänning en viktig funktion för en individs förståelse och interaktion med andra. Hittills har forskning bland annat upptäckt att förmågan kan se olika ut för kvinnor och män, där studierna ofta är baserat ur antingen ett biologiskt eller socialt synsätt. I denna systematiska översikt inkluderas båda dessa perspektiv för att granska vilket som könsskillnaderna, mellan vuxna kvinnor och män över 18 år, inom känsloigenkänning främst grundas i. Syftet var att undersöka hur neurovetenskapen bidrar till förståelsen av könsskillnaderna inom området. I litteratursökningen användes PubMed och Scopus där tio artiklar analyserades. Artiklarna hade störst fokus på och diskuterade främst biologiska könsskillnader i jämförelse med sociala faktorer, vilket utmynnade i en svårbedömd situation. Däremot kan det konstateras att det finns både sociala och biologiska könsskillnader som bidrar till känsloigenkänningens olikheter. Genom neurovetenskapens tekniker såsom EEG, fMRI och eye-tracking, har vi fått en bättre inblick i hur den typiska kvinnliga och manliga hjärnan fungerar i relation till bearbetning av andras känslor.

Emotional intelligence (EI) lies at the intersection of emotion and cognition and is seen as beneficial to our relationships and well-being. Yet, there is a gap in knowledge regarding the neural correlates of EI. There are three prevailing models defining the psychological construct of EI, the trait model, the ability model, and the mixed model. According to the ability model, EI consists of two facets - experiential and strategic EI. Experiential EI refers to abilities of perceiving and using emotions to facilitate thoughts, whereas strategic EI refers to abilities of understanding and managing emotions. This systematic review aims to investigate whether, and to what extent, the neural correlates of experiential and strategic EI rely on similar or different neural substrates. Five peer-reviewed studies met the inclusion criteria and were included. All the studies used Mayer-Salovey-Caruso Emotional Intelligence Test to measure EI. The brain imaging techniques used included structural and functional magnetic resonance imaging and diffusion tensor imaging. The findings of the review suggest that experiential and strategic EI rely partly on distinct and partly on common neural circuitry. Neural correlates associated primarily with strategic EI were gray matter volumes of ventromedial and ventrolateral prefrontal cortex and anterior and posterior insula. Both strategic and experiential EI were found to correlate with the rostral anterior cingulate cortex gray matter activation, and the effective connectivity of the anterior prefrontal cortex. Further research and development of measurement methodology are needed to deepen the understanding of strategic and experiential EI and their neural correlates.