A touch of hierarchy: population receptive fields reveal fingertip integration in Brodmann areas in human primary somatosensory cortex.

Several neuroimaging studies have shown the somatotopy of body part representations in primary somatosensory cortex (S1), but the functional hierarchy of distinct subregions in human S1 has not been adequately addressed. The current study investigates the functional hierarchy of cyto-architectonically distinct regions, Brodmann areas BA3, BA1, and BA2, in human S1. During functional MRI experiments, we presented participants with vibrotactile stimulation of the fingertips at three different vibration frequencies. Using population Receptive Field (pRF) modeling of the fMRI BOLD activity, we identified the hand region in S1 and the somatotopy of the fingertips. For each voxel, the pRF center indicates the finger that most effectively drives the BOLD signal, and the pRF size measures the spatial somatic pooling of fingertips. We find a systematic relationship of pRF sizes from lower-order areas to higher-order areas. Specifically, we found that pRF sizes are smallest in BA3, increase slightly towards BA1, and are largest in BA2, paralleling the increase in visual receptive field size as one ascends the visual hierarchy. Additionally, we find that the time-to-peak of the hemodynamic response in BA3 is roughly 0.5 s earlier compared to BA1 and BA2, further supporting the notion of a functional hierarchy of subregions in S1. These results were obtained during stimulation of different mechanoreceptors, suggesting that different afferent fibers leading up to S1 feed into the same cortical hierarchy.

Recruitment pattern of the diaphragm and extradiaphragmatic inspiratory muscles in response to different levels of pressure support.

BACKGROUND: Inappropriate ventilator assist plays an important role in the development of diaphragm dysfunction. Ventilator under-assist may lead to muscle injury, while over-assist may result in muscle atrophy. This provides a good rationale to monitor respiratory drive in ventilated patients. Respiratory drive can be monitored by a nasogastric catheter, either with esophageal balloon to determine muscular pressure (gold standard) or with electrodes to measure electrical activity of the diaphragm. A disadvantage is that both techniques are invasive. Therefore, it is interesting to investigate the role of surrogate markers for respiratory dive, such as extradiaphragmatic inspiratory muscle activity. The aim of the current study was to investigate the effect of different inspiratory support levels on the recruitment pattern of extradiaphragmatic inspiratory muscles with respect to the diaphragm and to evaluate agreement between activity of extradiaphragmatic inspiratory muscles and the diaphragm. METHODS: Activity from the alae nasi, genioglossus, scalene, sternocleidomastoid and parasternal intercostals was recorded using surface electrodes. Electrical activity of the diaphragm was measured using a multi-electrode nasogastric catheter. Pressure support (PS) levels were reduced from 15 to 3 cmH2O every 5 min with steps of 3 cmH2O. The magnitude and timing of respiratory muscle activity were assessed. RESULTS: We included 17 ventilated patients. Diaphragm and extradiaphragmatic inspiratory muscle activity increased in response to lower PS levels (36 ± 6% increase for the diaphragm, 30 ± 6% parasternal intercostals, 41 ± 6% scalene, 40 ± 8% sternocleidomastoid, 43 ± 6% alae nasi and 30 ± 6% genioglossus). Changes in diaphragm activity correlated best with changes in alae nasi activity (r2 = 0.49; P < 0.001), while there was no correlation between diaphragm and sternocleidomastoid activity. The agreement between diaphragm and extradiaphragmatic inspiratory muscle activity was low due to a high individual variability. Onset of alae nasi activity preceded the onset of all other muscles. CONCLUSIONS: Extradiaphragmatic inspiratory muscle activity increases in response to lower inspiratory support levels. However, there is a poor correlation and agreement with the change in diaphragm activity, limiting the use of surface electromyography (EMG) recordings of extradiaphragmatic inspiratory muscles as a surrogate for electrical activity of the diaphragm.

Changes in fMRI BOLD dynamics reflect anticipation to moving objects.

The human brain is thought to respond differently to novel versus predictable neural input. In human visual cortex, neural response amplitude to visual input might be determined by the degree of predictability. We investigated how fMRI BOLD responses in human early visual cortex reflect the anticipation of a single moving bar's trajectory. We found that BOLD signals decreased linearly from onset to offset of the stimulus trajectory. Moreover, decreased amplitudes of BOLD responses coincided with an increased initial dip as the stimulus moved along its trajectory. Importantly, motion anticipation effects were absent, when motion coherence was disrupted by means of stimulus contrast reversals. These results show that human early visual cortex anticipates the trajectory of a coherently moving object at the initial stages of visual motion processing. The results can be explained by suppression of predictable input, plausibly underlying the formation of stable visual percepts.

Predictions to motion stimuli in human early visual cortex: Effects of motion displacement on motion predictability.

Recently, several studies showed that fMRI BOLD responses to moving random dot stimuli are enhanced at the location of dot appearance, i.e., the motion trailing edge. Possibly, BOLD activity in human visual cortex reflects predictability of visual motion input. In the current study, we investigate to what extent fMRI BOLD responses reflect estimated predictions to visual motion. We varied motion displacement parameters (duration and velocity), while measuring BOLD amplitudes as a function of distance from the trailing edge. We have found that for all stimulus configurations, BOLD signals decrease with increasing distance from the trailing edge. This finding indicates that neural activity directly reflects the predictability of moving dots, rather than their appearance within classical receptive fields. However, different motion displacement parameters exerted only marginal effects on predictability, suggesting that early visual cortex does not literally predict motion trajectories. Rather, the results reveal a heuristic mechanism of motion suppression from trailing to leading edge, plausibly mediated through short-range horizontal connections. Simple heuristic suppression allows the visual system to recognize novel input among many motion signals, while being most energy efficient.

The Baha Softband. A new treatment for young children with bilateral congenital aural atresia.

The Baha (bone-anchored hearing aid) Softband appears to be an effective mean of hearing rehabilitation for children with a congenital bilateral aural atresia who are too young for the amplification of a Baha on an implant. The aided hearing threshold with a Baha Softband is almost equal to that achieved with a conventional bone conductor. The speech development of the children studied with a Baha Softband is on a par with peers with good hearing.

Quality improvement around the world: how much we can learn from each other.

The USA National Forum on Quality Improvement in Health Care--organised by the Institute of Healthcare Improvement (Boston USA)--attracts many people from outside North America. At the 1999 meeting 20 countries were represented. A session on "Quality improvement around the world" was included in the pre-conference programme to bring together people working in many countries to explore and compare their experiences in a programme of short presentations (table 1). This article draws together some of the themes that emerged from the presentations and from the discussion.