Fine-Scale Spatial Organization of Face and Object Selectivity in the Temporal Lobe: Do Functional Magnetic Resonance Imaging, Optical Imaging, and Electrophysiology Agree?

The spatial organization of the brain's object and face representations in the temporal lobe is critical for understanding high-level vision and cognition but is poorly understood. Recently, exciting progress has been made using advanced imaging and physiology methods in humans and nonhuman primates, and the combination of such methods may be particularly powerful. Studies applying these methods help us to understand how neuronal activity, optical imaging, and functional magnetic resonance imaging signals are related within the temporal lobe, and to uncover the fine-grained and large-scale spatial organization of object and face representations in the primate brain

Effects of Noise Bandwidth and Amplitude Modulation on Masking in Frog Auditory Midbrain Neurons

Natural auditory scenes such as frog choruses consist of multiple sound sources (i.e., individual vocalizing males) producing sounds that overlap extensively in time and spectrum, often in the presence of other biotic and abiotic background noise. Detection of a signal in such environments is challenging, but it is facilitated when the noise shares common amplitude modulations across a wide frequency range, due to a phenomenon called comodulation masking release (CMR). Here, we examined how properties of the background noise, such as its bandwidth and amplitude modulation, influence the detection threshold of a target sound (pulsed amplitude modulated tones) by single neurons in the frog auditory midbrain. We found that for both modulated and unmodulated masking noise, masking was generally stronger with increasing bandwidth, but it was weakened for the widest bandwidths. Masking was less for modulated noise than for unmodulated noise for all bandwidths. However, responses were heterogeneous, and only for a subpopulation of neurons the detection of the probe was facilitated when the bandwidth of the modulated masker was increased beyond a certain bandwidth – such neurons might contribute to CMR. We observed evidence that suggests that the dips in the noise amplitude are exploited by TS neurons, and observed strong responses to target signals occurring during such dips. However, the interactions between the probe and masker responses were nonlinear, and other mechanisms, e.g., selective suppression of the response to the noise, may also be involved in the masking release

A multi-disciplinary commentary on preclinical research to investigate vascular contributions to dementia

Although dementia research has been dominated by Alzheimer's disease (AD), most dementia in older people is now recognised to be due to mixed pathologies, usually combining vascular and AD brain pathology. Vascular cognitive impairment (VCI), which encompasses vascular dementia (VaD) is the second most common type of dementia. Models of VCI have been delayed by limited understanding of the underlying aetiology and pathogenesis. This review by a multidisciplinary, diverse (in terms of sex, geography and career stage), cross-institute team provides a perspective on limitations to current VCI models and recommendations for improving translation and reproducibility. We discuss reproducibility, clinical features of VCI and corresponding assessments in models, human pathology, bioinformatics approaches, and data sharing. We offer recommendations for future research, particularly focusing on small vessel disease as a main underpinning disorder

A Multi-disciplinary Commentary on Preclinical Research to investigate Vascular Contributions to Dementia

Although dementia research has been dominated by Alzheimer's disease (AD), most dementia in older people is now recognised to be due to mixed pathologies, usually combining vascular and AD brain pathology. Vascular cognitive impairment (VCI), which encompasses vascular dementia (VaD) is the second most common type of dementia. Models of VCI have been delayed by limited understanding of the underlying aetiology and pathogenesis. This review by a multidisciplinary, diverse (in terms of sex, geography and career stage), cross-institute team provides a perspective on limitations to current VCI models and recommendations for improving translation and reproducibility. We discuss reproducibility, clinical features of VCI and corresponding assessments in models, human pathology, bioinformatics approaches, and data sharing. We offer recommendations for future research, particularly focusing on small vessel disease as a main underpinning disorder.</p

Population characteristics of the responses to P+M_m and P+M_u.

<p><b>A:</b> Distribution of the different response functions (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031589#pone-0031589-g007" target="_blank">Fig. 7</a>) for P+M_m (black) and P+M_u (gray). ‘O’ indicates other types of responses. <b>B:</b> Median threshold increase () for M_m (black) and M_u (gray), as a function of masker bandwidth. Errorbars indicate interquartile ranges; large interquartile ranges point to the high variability in the neural responses. <b>C:</b> Relative occurrence of the different types of threshold curves for P+M_m (ordinate) and P+M_u (abscissa). The size of the dots indicates the percentage of neurons, with the largest dot corresponding to 17.5%. Combinations that can lead to CMR-type behavior are indicated in gray. <b>D:</b> Median detection thresholds for M_m (black) and M_u (gray) for the off-diagonal neurons (gray circles) in <b>C</b>.</p

Example of a neuron that shows overt time locking to the probe.

<p>The unit's responses to P+M_u at increasing probe level (<b>A</b>) show firing periodicity corresponding to the envelope of the probe. The number of spikes remained approximately constant for increasing probe levels (<b>B</b>, dashed line indicates response to noise alone) and <i>d</i>′ did not reach threshold, and thus the probe is not detectable based on the <i>d</i>′-method (<b>C</b>). However, the probe signal is clearly detectable based on the SC (<b>D</b>).</p

Effect of masker bandwidth on probe detection threshold.

<p><b>A–F:</b> RLFs for M_m; the dashed line indicates the RLF for the probe alone (P) and the solid line shows the mRLF for the probe in the presence of masker, while the dotted line shows the response to masker alone. The masked threshold is indicated by the gray dots. <b>G–L:</b> RLFs in response to M_u. <b>M:</b> detection thresholds as a function of the masker bandwidth for P+M_u (dashed line) and P+M_m (solid line).</p

The effect of labeling parameters on perfusion-based fMRI in nonhuman primates

The blood oxygenation level-dependent (BOLD) signal is the most commonly used modality of functional magnetic resonance imaging (fMRI) today. Although easy to implement, it is an ambiguous signal since it results from a combination of several hemodynamic factors. Functional cerebral blood flow changes, as measured by using arterial spin labeling (ASL), typically occur in the parenchyma and have been demonstrated to be more closely coupled to neural activation compared with BOLD. However, the intrinsically low signals from ASL techniques have hindered its widespread application to fMRI for basic research and even more so for clinical applications. Here, we report the first implementation of continuous ASL in the anaesthetized macaque at high magnetic field of 7 T. The technique was optimized to permit maximum signal-to-noise ratio of functional perfusion-based images at high spatial resolution. The effect of labeling parameters, such as label time and post-label delay (PLD), on functional cerebral blood flow (fCBF) in the visual cortex was evaluated. Functional cerebral blood flow maps did not change with increasing label time after 2,000 ms, indicating that a label time of 2,000 ms is sufficient for reliable mapping of fCBF. The percent changes obtained using fCBF were better localized to gray matter, than those obtained with BOLD. A short PLD of 200 ms revealed significantly higher fCBF changes at the cortical surface, indicating large-vessel contamination, than a long PLD of 800 ms. However, the effect of the PLD on fCBF was smaller than on baseline CBF. These results are of importance for high-resolution applications, and when accurate quantification is required for studies in monkeys as well as in humans