We physically interact with external stimuli when they occur within a limited space immediately surrounding the body, i.e., Peripersonal Space (PPS). In the primate brain, specific fronto-parietal areas are responsible for the multisensory representation of PPS, by integrating tactile, visual and auditory information occurring on and near the body. Dynamic stimuli are particularly relevant for PPS representation, as they might refer to potential harms approaching the body. However, behavioural tasks for studying PPS representation with moving stimuli are lacking. Here we propose a new dynamic audio-tactile interaction task in order to assess the extension of PPS in a more functionally and ecologically valid condition. Participants vocally responded to a tactile stimulus administered at the hand at different delays from the onset of task-irrelevant dynamic sounds which gave the impression of a sound source either approaching or receding from the subject’s hand. Results showed that a moving auditory stimulus speeded up the processing of a tactile stimulus at the hand as long as it was perceived at a limited distance from the hand, that is within the boundaries of PPS representation. The audio-tactile interaction effect was stronger when sounds were approaching compared to when sounds were receding. This study provides a new method to dynamically assess PPS representation: The function describing the relationship between tactile processing and the position of sounds in space can be used to estimate the location of PPS boundaries, along a spatial continuum between far and near space, in a valuable and ecologically significant way.

Variations in alpha rhythm have a significant role in perception and attention. Recently, alpha decrease has been associated with externally directed attention, especially in the visual domain, whereas alpha increase has been related to internal processing such as mental arithmetic. However, the role of alpha oscillations and how the different components of a task (processing of external stimuli, internal manipulation/representation, and task demand) interact to affect alpha power are still unclear. Here, we investigate how alpha power is differently modulated by attentional tasks depending both on task difficulty (less/more demanding task) and direction of attention (internal/external). To this aim, we designed two experiments that differently manipulated these aspects. Experiment 1, outside Virtual Reality (VR), involved two tasks both requiring internal and external attentional components (intake of visual items for their internal manipulation) but with different internal task demands (arithmetic vs. reading). Experiment 2 took advantage of the VR (mimicking an aircraft cabin interior) to manipulate attention direction: it included a condition of VR immersion only, characterized by visual external attention, and a condition of a purely mental arithmetic task during VR immersion, requiring neglect of sensory stimuli. Results show that: (1) In line with previous studies, visual external attention caused a significant alpha decrease, especially in parieto-occipital regions; (2) Alpha decrease was significantly larger during the more demanding arithmetic task, when the task was driven by external visual stimuli; (3) Alpha dramatically increased during the purely mental task in VR immersion, whereby the external stimuli had no relation with the task. Our results suggest that alpha power is crucial to isolate a subject from the environment, and move attention from external to internal cues. Moreover, they emphasize that the emerging use of VR associated with EEG may have important implications to study brain rhythms and support the design of artificial systems.

A mathematical model of short-term cardiovascular regulation is used to investigate how heart period variability reflects the action of the autonomic regulatory mechanisms (vagal and sympathetic). The model includes the pulsating heart, the systemic (splanchnic and extrasplanchnic) and pulmonary circulation, the mechanical effect of respiration on venous return, two groups of receptors (arterial baroreceptors and lung stretch receptors), the sympathetic and vagal efferent branches, and a very low-frequency (LF) vasomotor noise. All model parameters were given on the basis of physiological data from the literature. We used data from humans whenever possible, whereas parameters for the regulation loops are derived from dog experiments. The model, with basal parameter values, produces a heart period power spectrum with two distinct peaks [a high frequency (HF) peak at the respiratory rate and a LF peak at ∼0.1 Hz]. Sensitivity analysis on the mechanism gains suggests that the HF peak is mainly affected by the vagal mechanism, whereas the LF peak is increased by a high sympathetic gain and reduced by a high vagal gain. Moreover, the LF peak depends significantly on the reactivity of resistance vessels and is affected by noise, amplified by the sympathetic control loop at its resonance frequency. The model may represent a new tool to study alterations in the heart period spectrum on the basis of quantitative physiological hypotheses.

A mathematical model of the acute cardiovascular response to isocapnic hypoxia is presented. It includes a pulsating heart, the systemic and pulmonary circulation, a separate description of the vascular bed in organs with the higher metabolic need, and the local effect of O₂ on these organs. Moreover, the model also includes the action of several reflex regulatory mechanisms: the peripheral chemoreceptors, the lung stretch receptors, the arterial baroreceptors, and the hypoxic response of the central nervous system. All parameters in the model are given in accordance with the physiological literature. The simulated overall response to a deep hypoxia (28 mmHg) agrees with the experimental data quite well, showing a biphasic pattern. The early phase (8–10 s), caused by activation of peripheral chemoreceptors, exhibits a moderate increase in mean systemic arterial pressure, a decrease in heart rate, a quite constant cardiac output, and a redistribution of blood flow to the organs with higher metabolic need at the expense of other organs. The later phase (20 s) is characterized by the activation of lung stretch receptors and by the central nervous system hypoxic response. During this phase, cardiac output and heart rate increase together, and blood flow is restored to normal levels also in organs with lower metabolic need. The model may be used to gain a deeper understanding of the role of each mechanism in the overall cardiovascular response to hypoxia.

Attention is the ability to prioritize a set of information at expense of others and can be internally- or externally-oriented. Alpha and theta oscillations have been extensively implicated in attention. However, it is unclear how these oscillations operate when sensory distractors are presented continuously during task-relevant internal processes, in close-to-real-life conditions. Here, EEG signals from healthy participants were obtained at rest and in three attentional conditions, characterized by the execution of a mental math task (internal attention), presentation of pictures on a monitor (external attention), and task execution under the distracting action of picture presentation (internal-external competition). Alpha and theta power were investigated at scalp level and at some cortical regions of interest (ROIs); moreover, functional directed connectivity was estimated via spectral Granger Causality. Results show that frontal midline theta was distinctive of mental task execution and was more prominent during competition compared to internal attention alone, possibly reflecting higher executive control; anterior cingulate cortex appeared as mainly involved and causally connected to distant (temporal/occipital) regions. Alpha power in visual ROIs strongly decreased in external attention alone, while it assumed values close to rest during competition, reflecting reduced visual engagement against distractors; connectivity results suggested that bidirectional alpha influences between frontal and visual regions could contribute to reduce visual interference in internal attention. This study can help to understand how our brain copes with internal-external attention competition, a condition intrinsic in the human sensory-cognitive interplay, and to elucidate the relationships between brain oscillations and attentional functions/dysfunctions in daily tasks.

Neurophysiological and behavioral studies suggest that the peripersonal space is represented in a multisensory fashion by integrating stimuli of different modalities. We developed a neural network to simulate the visual-tactile representation of the peripersonal space around the right and left hands. The model is composed of two networks (one per hemisphere), each with three areas of neurons: two are unimodal (visual and tactile) and communicate by synaptic connections with a third downstream multimodal (visual-tactile) area. The hemispheres are interconnected by inhibitory synapses. We applied a combination of analytic and computer simulation techniques. The analytic approach requires some simplifying assumptions and approximations (linearization and a reduced number of neurons) and is used to investigate network stability as a function of parameter values, providing some emergent properties. These are then tested and extended by computer simulations of a more complex nonlinear network that does not rely on the previous simplifications. With basal parameter values, the extended network reproduces several in vivo phenomena: multisensory coding of peripersonal space, reinforcement of unisensory perception by multimodal stimulation, and coexistence of simultaneous right- and left-hand representations in bilateral stimulation. By reducing the strength of the synapses from the right tactile neurons, the network is able to mimic the responses characteristic of right-brain-damaged patients with left tactile extinction: perception of unilateral left tactile stimulation, cross-modal extinction and cross-modal facilitation in bilateral stimulation. Finally, a variety of sensitivity analyses on some key parameters was performed to shed light on the contribution of single-model components in network behaviour. The model may help us understand the neural circuitry underlying peripersonal space representation and identify its alterations explaining neurological deficits. In perspective, it could help in interpreting results of psychophysical and behavioral trials and clarifying the neural correlates of multisensory-based rehabilitation procedures.