Biology subjects

Barbas, H.

Publications and source records attributed to Barbas, H..

3 recordsLinked to original sources

bioRxiv2022

Sleep spindles in primates: modelling the effects of distinct laminar thalamocortical connectivity in core, matrix, and reticular thalamic circuits

Sleep spindles are associated with the beginning of deep sleep and memory consolidation and are disrupted in schizophrenia and autism. In primates, distinct core and matrix thalamocortical (TC) circuits regulate sleep-spindle activity, through communications that are filtered by the inhibitory thalamic reticular nucleus (TRN) however, little is known about typical TC network interactions and the mechanisms that are disrupted in brain disorders. We developed a primate-specific, circuit-based TC computational model with distinct core and matrix loops that can simulate sleep spindles. We implemented novel multilevel cortical and thalamic mixing, and included local thalamic inhibitory interneurons, and direct layer 5 projections of variable density to TRN and thalamus to investigate the functional consequences of different ratios of core and matrix node connectivity contribution to spindle dynamics. Our simulations showed that spindle power in primates can be modulated based on the level of cortical feedback, thalamic inhibition, and engagement of model core vs. matrix, with the latter having a greater role in spindle dynamics. The study of the distinct spatial and temporal dynamics of core-, matrix-, and mix-generated sleep spindles establishes a framework to study disruption of TC circuit balance underlying deficits in sleep and attentional gating seen in autism and schizophrenia.

neuroscience↗

bioRxiv2022

Emotional intensity can enrich or degrade memories: impact of the amygdalar pathway on hippocampus through inhibitory neurons

The brains emotional system powerfully modulates processing of context and episodic memory. A key pathway that mediates these effects is the projection from the amygdala to the hippocampus. Wang and Barbas (1) uncovered a distinctive pattern in the pathways from amygdala to hippocampus in primates. In hippocampal CA3, a pathway from the amygdala innervated excitatory pyramidal neurons as well as parvalbumin (PV) and calretinin (CR) inhibitory neurons. In hippocampal CA1, amygdalar projections also innervated pyramidal neurons and CR interneurons, but not PV interneurons. The effects of these complex circuits can best be probed using computational simulations. We developed a model of spiking neurons to investigate the implications and significance of these amygdala-hippocampal circuits for affective influence on processing mnemonic context, and to test their effects as input from the amygdala gradually increased. Our simulations revealed that moderate input from the amygdala can enhance detail in CA3 representations that can correctly sort out contexts and episodes from memory. However, high amygdalar input suppressed CA3 responses to non-amygdalar inputs through powerful inhibitory neurons, leading to memory representations that lack detail. Moreover, high amygdalar input prematurely hastened the timing of responses in CA1 occurring when the current situation broadly and non-specifically matched a remembered context. Amygdalar pathways to hippocampus enable a mechanism whereby affective signaling appropriately enhances hippocampal representations of remembered context. However, when amygdalar input is excessive in high emotional arousal, there is loss of memory detail and overgeneralization, as seen in post-traumatic stress disorder or pathologic phobias.

neuroscience↗

bioRxiv2021

The Cortical Spectrum: a robust structural continuum in primate cerebral cortex revealed by histological staining and magnetic resonance imaging

High-level characterizations of the primate cerebral cortex sit between two extremes: on one end the cortical mantle is seen as a mosaic of structurally and functionally unique areas, and on the other it is seen as a uniform six-layered structure in which functional differences are defined solely by extrinsic connections. Neither of these extremes captures the crucial neuroanatomical finding: that the cortex exhibits systematic gradations in architectonic structure. These gradations have been shown to predict cortico-cortical connectivity, which in turn suggests powerful ways to ground connectomics in anatomical structure, and by extension cortical function. A challenge to more widespread use of this concept is the labor-intensive and invasive nature of histological staining, which is the primary means of recognizing anatomical gradations. Here we show that a novel computational analysis technique can be used to derive a coarse-grained picture of cortical variation. For each of 78 cortical areas spanning the entire cortical mantle of the rhesus macaque, we created a high dimensional set of anatomical features derived from captured images of cortical tissue stained for myelin and SMI-32. The method involved semi-automated de-noising of images, and enabled comparison of brain areas without hand-labeling of features such as layer boundaries. We applied nonmetric multidimensional scaling (NMDS) to the dataset to visualize similarity among cortical areas. This analysis shows a systematic variation between weakly laminated (limbic) cortices and sharply laminated (eulaminate) cortices. We call this smooth continuum the cortical spectrum. We also show that this spectrum is visible within subsystems of the cortex: the occipital, parietal, temporal, motor, prefrontal, and insular cortices. We compared the NMDS-derived spectrum with a spectrum produced using T1- and T2-weighted magnetic resonance imaging (MRI) data derived from macaque, and found close agreement of the two coarse-graining methods. This evidence suggests that T1/T2 data, routinely obtained in human MRI studies, can be used as an effective proxy for data derived from high-resolution histological methods. More generally, this approach shows that the cortical spectrum is robust to the specific method used to compare cortical areas, and is therefore a powerful tool to understand the principles of organization of the primate cortex.

neuroscience↗