Summary Touch perception depends on integrating signals from multiple types of peripheral mechanoreceptors. Merkel-cell associated afferents are thought to play a major role in form perception by encoding surface features of touched objects. However, activity of Merkel afferents during active touch has not been directly measured. Here, we show that Merkel and unidentified slowly adapting afferents in the whisker system of behaving mice respond to both self-motion and active touch. Touch responses were dominated by sensitivity to bending moment (torque) at the base of the whisker and its rate of change, and largely explained by a simple mechanical model. Self-motion responses encoded whisker position within a whisk cycle (phase), not absolute whisker angle, and arose from stresses reflecting whisker inertia and activity of specific muscles. Thus, Merkel afferents send to the brain multiplexed information about whisker position and surface features, suggesting that proprioception and touch converge at the earliest neural level.

Timing has been proposed as a basic function of the cerebellar cortex (particularly the climbing fiber afferents and their sole source, the inferior olive) that explains the contribution of the cerebellum to both motor control and nonmotor cognitive functions. However, whether the olivo-cerebellar system mediates time perception without motor behavior remains controversial. We used event-related functional magnetic resonance imaging to dissociate the neural correlates of the perceptual from the motor aspects of timing. The results show activation of multiple areas within the cerebellar cortex during both perception and motor performance of temporal sequences. The results further show that the inferior olive was activated only when subjects perceived the temporal sequences without motor activity. This finding is most consistent with electrophysiological studies showing decreased responsiveness of the inferior olivary neurons to sensory input during expected, self-produced movement. Our results suggest that the primary role of the inferior olive and the climbing fiber system in timing is the encoding of temporal information independent of motor behavior.

Dendrite development of newborn granule cells (GCs) in the dentate gyrus of adult hippocampus is critical for their incorporation into existing hippocampal circuits, but the cellular mechanisms regulating their dendrite development remains largely unclear. In this study, we examined the function of brain-derived neurotrophic factor (BDNF), which is expressed in adult-born GCs, in regulating their dendrite morphogenesis. Using retrovirus-mediated gene transfection, we found that deletion and overexpression of BDNF in adult-born GCs resulted in the reduction and elevation of dendrite growth, respectively. This effect was mainly due to the autocrine rather than paracrine action of BDNF, because deletion of BDNF only in the newborn GCs resulted in dendrite abnormality of these neurons to a similar extent as that observed in conditional knockout (cKO) mice with BDNF deleted in the entire forebrain. Furthermore, selective expression of BDNF in adult-born GCs in BDNF cKO mice fully restored normal dendrite development. The BDNF autocrine action was also required for the development of normal density of spines and normal percentage of spines containing the postsynaptic marker PSD-95, suggesting autocrine BDNF regulation of synaptogenesis. Furthermore, increased dendrite growth of adult-born GCs caused by voluntary exercise was abolished by BDNF deletion specifically in these neurons and elevated dendrite growth due to BDNF overexpression in these neurons was prevented by reducing neuronal activity with coexpression of inward rectifier potassium channels, consistent with activitydependent autocrine BDNF secretion. Therefore, BDNF expressed in adult-born GCs plays a critical role in dendrite development by acting as an autocrine factor.

Brain activation underlying language processing in Chinese-English bilinguals was examined using fMRI in an orthographic search and a semantic classification task. In both tasks, brain areas activated by Chinese characters and English words were very similar to tasks examining Chinese reading using Chinese pinyin (an alphabetic Chinese script) and Chinese characters. However, the degree of later-alization was different, with English words (second language) causing much more right hemisphere activation than Chinese characters (native language). These differences support the hypothesis that second language usage causes more right hemisphere activation than native language usage.

No abstract

No abstract

No abstract

The inferior olive is the sole source of the climbing fiber system, one of the two major afferent systems of the cerebellum; however, its exact role remains unknown. A longstanding hypothesis is that the inferior olive with its unique intrinsic rhythmic firing properties mediates motor timing. However, direct evidence linking the inferior olive to timing behavior has been difficult to demonstrate in animal or human studies likely due to the inhibition of inferior olive responses by self-produced movement. Here we used event-related functional magnetic resonance imaging (fMRI) and a perceptual task that dissociates the temporal from nontemporal attributes of sensory input. Subjects were asked to attend to rhythmically occurring identical visual stimuli and to detect a change in their timing, spatial orientation, or color. Inferior olive activation was seen only when perceiving a change in stimulus timing. These results are consistent with animal studies demonstrating that the inferior olive is especially sensitive to "unexpected" sensory events and further provide evidence supporting the specificity of the inferior olive response to stimulus timing. The results are consistent with the view that the inferior olive and the climbing fiber system mediate the encoding of temporal information required for both motor and nonmotor cognitive processes.