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NeuroBlogs Daily

June 27, 2023

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SCIENCE

Age differences in neural distinctiveness during memory encoding, retrieval, and
reinstatement Robust evidence points to mnemonic deficits in older adults
related to dedifferentiated, i.e. less distinct, neural responses during memory
encoding. However, less is known about retrieval-related dedifferentiation and
its role in age-related memory decline. In this study, younger and older adults
were scanned both while incidentally learning face and house stimuli and while
completing a surprise recognition memory test. Using pattern similarity
searchlight analyses, we looked for indicators of neural dedifferentiation
during encoding, retrieval, and encoding–retrieval reinstatement. Our findings
revealed age-related reductions in neural distinctiveness during all memory
phases in visual processing regions. Interindividual differences in retrieval-
and reinstatement-related distinctiveness were strongly associated with
distinctiveness during memory encoding. Both item- and category-level
distinctiveness predicted trial-wise mnemonic outcomes. We further demonstrated
that the degree of neural distinctiveness during encoding tracked
interindividual variability in memory performance better than both retrieval-
and reinstatement-related distinctiveness. All in all, we contribute to meager
existing evidence for age-related neural dedifferentiation during memory
retrieval. We show that neural distinctiveness during retrieval is likely tied
to recapitulation of encoding-related perceptual and mnemonic processes.

Development of the hippocampal CA2 region and the emergence of social
recognition Social memories formed in early life, like those for family and
unrelated peers, are known to contribute to healthy social interactions
throughout life, although how the developing brain supports social memory
remains relatively unexplored. The CA2 subregion of the hippocampus is involved
in social memory function, but most literature on this subject is restricted to
studies of adult rodents. Here, we review the current literature on the
embryonic and postnatal development of hippocampal subregion CA2 in mammals,
with a focus on the emergence of its unusual molecular and cellular
characteristics, including its notably high expression of plasticity-suppressing
molecules. We also consider the connectivity of the CA2 with other brain areas,
including intrahippocampal regions, such as the dentate gyrus, CA3, and CA1
regions, and extrahippocampal regions, such as the hypothalamus, ventral
tegmental area, basal forebrain, raphe nuclei, and the entorhinal cortex. We
review developmental milestones of CA2 molecular, cellular, and circuit-level
features that may contribute to emerging social recognition abilities for kin
and unrelated conspecifics in early life. Lastly, we consider genetic mouse
models related to neurodevelopmental disorders in humans in order to survey
evidence about whether atypical formation of the CA2 may contribute to social
memory dysfunction.

Beta band rhythms influence reaction times Despite their involvement in many
cognitive functions, beta oscillations are among the least understood brain
rhythms. Reports on whether the functional role of beta is primarily inhibitory
or excitatory have been contradictory. Our framework attempts to reconcile these
findings and proposes that several beta rhythms co-exist at different
frequencies. Beta frequency shifts and their potential influence on behavior
have thus far received little attention. In this human magnetoencephalography
experiment, we asked whether changes in beta power or frequency in auditory
cortex and motor cortex influence behavior (reaction times) during an auditory
sweep discrimination task. We found that in motor cortex, increased
beta power slowed down responses, while in auditory cortex, increased
beta frequency slowed down responses. We further characterized beta as transient
burst events with distinct spectro-temporal profiles influencing reaction times.
Finally, we found that increased motor-to-auditory beta connectivity also slowed
down responses. In sum, beta power, frequency, bursting properties, cortical
focus, and connectivity profile all influenced behavioral outcomes. Our results
imply that the study of beta oscillations requires caution as beta dynamics are
multifaceted phenomena, and that several dynamics must be taken into account to
reconcile mixed findings in the literature.

The effects of episode spacing on adult’s reports of a repeated event Witnesses’
reports of repeated events have been the focus of much research; however, the
spacing interval between each episode of the event has differed greatly. The aim
of the current study was to determine whether spacing interval affects
participants’ memory reports. Adults (N = 217) watched one (n = 52) or four
videos depicting workplace bullying. The repeated event participants watched the
four videos all in one day (n = 55), one per day over four consecutive days
(n = 60), or one every three days over 12 days (n = 50). One week after the last
(or only) video, participants reported on that video and answered some
reflective questions about the procedure. Repeated-event participants also
reported on what usually happens across the videos. Single-event participants
reported proportionally more accurate information about the target video than
repeated-event participants, and spacing interval did not affect repeated event
participants’ accuracy. However, accuracy scores were close to ceiling while
errors rates were at floor levels, preventing us from drawing strong
conclusions. We found some evidence that episode spacing affected
participants’ perceptions of their memory performance. Overall, spacing may have
a minimal effect on adults’ memory for repeated events, but further research is
required.

Multi-level analysis of the gut–brain axis shows autism spectrum
disorder-associated molecular and microbial profiles Autism spectrum disorder
(ASD) is a neurodevelopmental disorder characterized by heterogeneous cognitive,
behavioral and communication impairments. Disruption of the gut–brain axis (GBA)
has been implicated in ASD although with limited reproducibility across studies.
In this study, we developed a Bayesian differential ranking algorithm to
identify ASD-associated molecular and taxa profiles across 10 cross-sectional
microbiome datasets and 15 other datasets, including dietary patterns,
metabolomics, cytokine profiles and human brain gene expression profiles. We
found a functional architecture along the GBA that correlates with heterogeneity
of ASD phenotypes, and it is characterized by ASD-associated amino acid,
carbohydrate and lipid profiles predominantly encoded by microbial species in
the genera Prevotella, Bifidobacterium, Desulfovibrio and Bacteroides and
correlates with brain gene expression changes, restrictive dietary patterns and
pro-inflammatory cytokine profiles. The functional architecture revealed in
age-matched and sex-matched cohorts is not present in sibling-matched cohorts.
We also show a strong association between temporal changes in microbiome
composition and ASD phenotypes. In summary, we propose a framework to leverage
multi-omic datasets from well-defined cohorts and investigate how the GBA
influences ASD.

Anatomical and functional predictors of disorientation after first-ever brain
damage Disorientation is a frequent consequence of acute brain injury or diffuse
disorders, such as confusional states or dementia. Its anatomical correlates are
debated. Impaired memory as its commonly assumed mechanism predicts that
disorientation is associated with medial temporal damage. The alternative is
that disorientation reflects defective orbitofrontal reality filtering (ORFi) –
a specific failure to identify whether thoughts or memories refer to present
reality or not. The latter is a function of the posterior orbitofrontal cortex
and connected structures. This study examined the mechanisms and anatomical
basis of disorientation in an unselected group of patients with first-ever
subacute brain injury

HDL anti-inflammatory function is impaired and associated with high SAA1 and low
APOA4 levels in aneurysmal subarachnoid hemorrhage Aneurysmal subarachnoid
hemorrhage (aSAH) is a devastating disease with high morbidity and mortality
rates. Within 24 hours after aSAH, monocytes are recruited and enter the
subarachnoid space, where they mature into macrophages, increasing the
inflammatory response and contributing, along with other factors, to delayed
neurological dysfunction and poor outcomes. High-density lipoproteins (HDL) are
lipid-protein complexes that exert anti-inflammatory effects but under
pathological conditions undergo structural alterations that have been associated
with loss of functionality. Plasma HDL were isolated from patients with aSAH and
analyzed for their anti-inflammatory activity and protein composition. HDL
isolated from patients lost the ability to prevent VCAM-1 expression in
endothelial cells (HUVEC) and subsequent adhesion of THP-1 monocytes to the
endothelium. Proteomic analysis showed that HDL particles from patients had an
altered composition compared to those of healthy subjects. We confirmed by
western blot that low levels of apolipoprotein A4 (APOA4) and high of serum
amyloid A1 (SAA1) in HDL were associated with the lack of anti-inflammatory
function observed in aSAH. Our results indicate that the study of HDL in the
pathophysiology of aSAH is needed, and functional HDL supplementation could be
considered a novel therapeutic approach to the treatment of the inflammatory
response after aSAH.

About the compatibility between the perturbational complexity index and the
global neuronal workspace theory of consciousness This paper investigates the
compatibility between the theoretical framework of the global neuronal workspace
theory (GNWT) of conscious processing and the perturbational complexity index
(PCI). Even if it has been introduced within the framework of a concurrent
theory (i.e. Integrated Information Theory), PCI appears, in principle,
compatible with the main tenet of GNWT, which is a conscious process that
depends on a long-range connection between different cortical regions, more
specifically on the amplification, global propagation, and integration of brain
signals. Notwithstanding this basic compatibility, a number of limited
compatibilities and apparent differences emerge. This paper starts from the
description of brain complexity, a notion that is crucial for PCI, to then
summary of the main features of PCI and the main tenets of GNWT. Against this
background, the text explores the compatibility between PCI and GNWT. It
concludes that GNWT and PCI are fundamentally compatible, even though there are
some partial disagreements and some points to further examine.

New insights into hypothalamic neurogenesis disruption after acute and intense
stress: implications for microglia and inflammation In recent years, the
hypothalamus has emerged as a new neurogenic area, capable of generating new
neurons after development. Neurogenesis-dependent neuroplasticity seems to be
critical to continuously adapt to internal and environmental changes. Stress is
a potent environmental factor that can produce potent and enduring effects on
brain structure and function. Acute and chronic stress is known to cause
alterations in neurogenesis and microglia in classical adult neurogenic regions
such as the hippocampus. The hypothalamus is one of the major brain regions
implicated in homeostatic stress and emotional stress systems, but little is
known about the effect of stress on the hypothalamus. Here, we studied the
impact of acute and intense stress (water immersion and restrain stress, WIRS),
which may be considered as an inducer of an animal model of posttraumatic stress
disorder, on neurogenesis and neuroinflammation in the hypothalamus of adult
male mice, focusing on three nuclei: PVN, VMN and ARC, and also in the
periventricular area. Our data revealed that a unique stressor was sufficient to
provoke a significant impact on hypothalamic neurogenesis by inducing a
reduction in the proliferation and number of immature neurons identified as DCX+
cells. These differences were accompanied by marked microglial activation in the
VMN and ARC, together with a concomitant increase in IL-6 levels, indicating
that WIRS induced an inflammatory response. To investigate the possible
molecular mechanisms responsible for neuroplastic and inflammatory changes, we
tried to identify proteomic changes. The data revealed that WIRS induced changes
in the hypothalamic proteome, modifying the abundance of three and four proteins
after 1 h or 24 h of stress application, respectively. These changes were also
accompanied by slight changes in the weight and food intake of the animals.
These results are the first to show that even a short-term environmental
stimulus such as acute and intense stress can have neuroplastic, inflammatory,
functional and metabolic consequences on the adult hypothalamus.



A Grey Matter: In the fight to find a cure for motor neurone disease Tom HighamThe World Before Us: The New Science Behind Our Human Origins

NavNeuro 121: The Brain in Space – With Dr. Vonetta Dotson

bjks 73. Tom Hostler: Open science, workload, and academic capitalism

PBtS 714: Dr. Christy Haynes on Tiny Technology with Big Impacts: Nanoparticles for Medicine, Energy, and the Environment


PEL 320: Friedrich Schlegel on Romanticism (Part One)


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