Functional Hallmarks of Healthy Macrophage Responses: Their Regulatory Basis and Disease Relevance

Macrophages are first responders for the immune system. In this role, they have both effector functions for neutralizing pathogens and sentinel functions for alerting other immune cells of diverse pathologic threats, thereby initiating and coordinating a multipronged immune response. Macrophages are distributed throughout the body-they circulate in the blood, line the mucosal membranes, reside within organs, and survey the connective tissue. Several reviews have summarized their diverse roles in different physiological scenarios and in the initiation or amplification of different pathologies. In this review, we propose that both the effector and the sentinel functions of healthy macrophages rely on three hallmark properties: response specificity, context dependence, and stimulus memory. When these hallmark properties are diminished, the macrophage's biological functions are impaired, which in turn results in increased risk for immune dysregulation, manifested by immune deficiency or autoimmunity. We review the evidence and the molecular mechanisms supporting these functional hallmarks.

Domain generality versus modality specificity: the paradox of statistical learning

Statistical learning (SL) is typically considered to be a domain-general mechanism by which cognitive systems discover the underlying distributional properties of the input. However, recent studies examining whether there are commonalities in the learning of distributional information across different domains or modalities consistently reveal modality and stimulus specificity. Therefore, important questions are how and why a hypothesized domain-general learning mechanism systematically produces such effects. Here, we offer a theoretical framework according to which SL is not a unitary mechanism, but a set of domain-general computational principles that operate in different modalities and, therefore, are subject to the specific constraints characteristic of their respective brain regions. This framework offers testable predictions and we discuss its computational and neurobiological plausibility.

Stimulus specificity and dishabituation of operant responding in humans

Habituation has recently been addressed within the operant conditioning paradigm. While the literature on this topic is growing, the examination of dishabituation, a fundamental characteristic of habituation, remains limited. This study expanded research on habituation of operant responding in non-human animals to research involving humans. Specifically, dishabituation and stimulus specificity were examined under a variety of conditions involving changes in the reinforcer type, reinforcement schedule, reinforcer amount, and selected properties of the antecedent stimuli for a computerized task with 46 undergraduate students. An additional 3 participants were exposed to a control condition. Evaluation of within session patterns of responding indicates that the introduction of stimulus changes into the operant context reliably produced dishabituation of operant responding in humans.

Physiological and anatomical organization of multiwhisker response interactions in the barrel cortex of rats

To understand the physiological properties and anatomical organization of the spatiotemporal interaction of the responses to multiwhisker stimulation in neurons of the rat barrel cortex, single-unit recordings of 114 neurons were performed across all layers (layer II/III, n = 39; IV, n = 33; V/VI, n = 42) of the posteromedial barrel subfield of the primary somatosensory cortex of anesthetized rats. Two neighboring principal and adjacent whiskers (PW and AW, respectively) in the same row were deflected rostrally or caudally at varying interstimulus intervals (ISIs). In 37% of the neurons, the response to the combined stimulus was significantly larger than the sum of the responses to stimulation of the individual whiskers. In instances in which response facilitation was observed, selectivity was noted for the combination (75%) of the PW with a particular AW or for a particular direction (60%) of whisker deflection. The direction bias of the responses to multiwhisker stimulation was well correlated with that of the sum of the responses to single whisker stimulation (r = 0.83; p < 0.001). The pattern and magnitude of the response interaction in the neurons of the superficial layers were closely related to the location of the recorded cell in the barrel columns. Multiwhisker stimulation at short ISIs (</=3 msec) evoked prominent response facilitation in cells located close to the border between two columns (p < 0.05, one-way ANOVA), where two excitatory inputs were expected to arrive at the same time. Our results suggest that the spatiotemporal patterns of multiwhisker stimulation, such as whisker combination, direction of deflection, and timing, are expressed as different magnitudes of response interaction, which depends on the proximity of cells to home and adjacent barrel columns.