Neuroscience
-
The receptive fields of many auditory cortical neurons are multidimensional and are best represented by more than one stimulus feature. The number of these dimensions, their characteristics, and how they differ with stimulus context have been relatively unexplored. Standard methods that are often used to characterize multidimensional stimulus selectivity, such as spike-triggered covariance (STC) or maximally informative dimensions (MIDs), are either limited to Gaussian stimuli or are only able to recover a small number of stimulus features due to data limitations. ⋯ Excitatory and suppressive features coded different acoustic contexts: excitatory features encoded higher temporal and spectral modulations, while suppressive features had lower modulation frequency preferences. We found that the excitatory and suppressive features themselves were sensitive to stimulus context when we employed two stimuli that differed only in their short-term correlation structure: while the linear features were similar, the secondary features were strongly affected by stimulus statistics. These results show that multidimensional receptive field processing is influenced by feature type and stimulus context.
-
Studies of major depressive disorder (MDD) in postmortem brain tissue report enhanced binding to inhibitory serotonin-1A autoreceptors in midbrain dorsal raphe and reductions in length of axons expressing the serotonin transporter (SERT) in dorsolateral prefrontal cortex. The length density of axons expressing SERT in the orbitofrontal cortex (OFC) was determined in 18 subjects with MDD and 17 age-matched control subjects. A monoclonal antibody was used to immunohistochemically label the SERT in fixed sections of OFC. ⋯ Neither gender, tissue pH, postmortem interval, 5-HTTLPR genotype, time in fixative, nor death by suicide had a significant effect on axon length. The age-related decrease in SERT-ir axon length in MDD may reflect pathology of ascending axons passing through deep white matter hyperintensities. Greater length of axons expressing SERT in younger subjects with MDD may result in a significant deficit in serotonin availability in OFC.
-
Explicit negative attitudes toward obese individuals are well documented and seem to modulate the activity of perceptual areas, such as the Extrastriate Body Area (EBA) in the lateral occipito-temporal cortex, which is critical for body-shape perception. Nevertheless, it is still unclear whether EBA serves a role in implicit weight-stereotypical bias, thus reflecting stereotypical trait attribution on the basis of perceptual cues. Here, we used an Implicit Association Test (IAT) to investigate whether applying transcranial direct current stimulation (tDCS) over bilateral extrastriate visual cortex reduces pre-existing implicit weight stereotypical associations (i.e. "Bad" with Fat and "Good" with Slim, valence-IAT). ⋯ Furthermore, the effect was specific for the polarity and hemisphere of stimulation. Importantly, tDCS affected the responses only in male participants, who presented a reliable weight-bias during sham condition, but not in female participants, who did not show reliable weight-bias at sham condition. The present results suggest that negative attitudes toward obese individuals may reflect neural signals from the extrastriate visual cortex.
-
The superior temporal gyrus (STG) is involved in speech recognition against informational masking under cocktail-party-listening conditions. Compared to healthy listeners, people with schizophrenia perform worse in speech recognition under informational speech-on-speech masking conditions. It is not clear whether the schizophrenia-related vulnerability to informational masking is associated with certain changes in FC of the STG with some critical brain regions. ⋯ The results showed that in healthy participants, but not participants with schizophrenia, the contrast of either the PSS or PSC condition against the masker-only condition induced an enhancement of functional connectivity (FC) of the STG with the left superior parietal lobule and the right precuneus. Compared to healthy participants, participants with schizophrenia showed declined FC of the STG with the bilateral precuneus, right SPL, and right supplementary motor area. Thus, FC of the STG with the parietal areas is normally involved in speech listening against informational masking under either the PSS or PSC conditions, and declined FC of the STG in people with schizophrenia with the parietal areas may be associated with the increased vulnerability to informational masking.
-
Prolonged low-level noise exposure alters loudness perception in humans, presumably by decreasing the gain of the central auditory system. Here we test the central gain hypothesis by measuring the acute and chronic physiologic changes at the level of the cochlea and inferior colliculus (IC) after a 75-dB SPL, 10-20-kHz noise exposure for 5weeks. The compound action potential (CAP) and summating potential (SP) were used to assess the functional status of the cochlea and 16 channel electrodes were used to measure the local field potentials (LFP) and multi-unit spike discharge rates (SDR) from the IC immediately after and one-week post-exposure. ⋯ Surprisingly, one-week post-exposure supra-threshold responses from the cochlea had not only recovered, but were significantly larger than normal, and thresholds were significantly better than controls. Moreover, sound-evoked hyperactivity in the IC was sustained within the noise exposure frequency band but suppressed at higher frequencies. When response amplitudes representing the neural output of the cochlea and IC activity at one-week post exposure were compared with control animal responses, a central attenuation phenomenon becomes evident, which may play a key role in understanding why low-level noise can sometimes ameliorate tinnitus and hyperacusis percepts.