Disynaptic cerebrocerebellar pathways originating from multiple functionally distinct cortical areas

The cerebral cortex and cerebellum both play important roles in sensorimotor processing, however, precise connections between these major brain structures remain elusive. Using anterograde mono-trans-synaptic tracing, we elucidate cerebrocerebellar pathways originating from primary motor, sensory, and association cortex. We confirm a highly organized topography of corticopontine projections in mice; however, we found no corticopontine projections originating from primary auditory cortex and detail several potential extra-pontine cerebrocerebellar pathways. The cerebellar hemispheres were the major target of resulting disynaptic mossy fiber terminals, but we also found at least sparse cerebrocerebellar projections to every lobule of the cerebellum. Notably, projections originating from association cortex resulted in less laterality than primary sensory/motor cortices. Within molecularly defined cerebellar modules we found spatial overlap of mossy fiber terminals, originating from functionally distinct cortical areas, within crus I, paraflocculus, and vermal regions IV/V and VI - highlighting these regions as potential hubs for multimodal cortical influence.

Object Recognition’s Garden Path: Low Spatial Frequencies

Several experiments, notably one done by Bruner and Potter (1964), have demonstrated delayed object recognition when viewing a blurred image gradually come into focus. Bruner and Potter (1964) suggested that the wrong answer is held until there is an obvious contradiction. Others have hypothesized that “competitive activation” is responsible for delayed recognition. The results of the experiments reported in this paper are consistent with a third hypothesis, that delayed recognition is due to an initial organization of image elements that is incompatible with correct recognition and that the initial grouping and figure-ground perception, among other aspects of organization, drive subsequent perception via top-down cortical pathways. A total of 7 experiments using 3 forms of degradation supported this hypothesis. Images degraded by low-pass filtering produced significant delay in recognition, while degradation by fragmentation did not, and a third form of degradation similar to fragmentation mitigated the effect. The experiments also demonstrate that if images are low-pass filtered delayed recognition occurs with presentations of as little as 100 ms and early presentations lead to delayed recognition over long intertrial intervals, at least 105 seconds. Further, support for the hypothesis that top-down cortical influence is key to this phenomenon came from an experiment showing that masking eliminates delayed recognition for short presentations. Taken together these results support a hypothesis that delayed recognition is due to errors in perceptual organization that lead to incorrect responses and these errors are fostered by low spatial frequencies.

Aversive Learning Increases Release Probability of Olfactory Sensory Neurons

Predicting danger from previously associated sensory stimuli is essential for survival. Contributions from altered peripheral sensory inputs are implicated in this process, but the underlying mechanisms remain elusive. Here we use the mammalian olfactory system to investigate such mechanisms. Primary olfactory sensory neurons (OSNs) project their axons directly to the olfactory bulb (OB) glomeruli where their synaptic release is subject to local and cortical influence and neuromodulation. Pairing optogenetic activation of a single glomerulus with foot shock in mice induces freezing to the light stimulation alone during fear retrieval. This is accompanied by an increase in OSN release probability and a reduction in GABAB receptor expression in the conditioned glomerulus. Furthermore, freezing time is positively correlated with the release probability of OSNs in fear conditioned mice. These results suggest that aversive learning increases peripheral olfactory inputs at the first synapse, which may contribute to the behavioral outcome.

Evidence for a Cortically Mediated Release from Inhibition in the Human Cochlea

Purpose: To determine cortical influence on the efferent medial olivocochlear bundle system. Research Design: The effects of attention on contralateral suppression (CS) of click-evoked otoacoustic emissions were measured. Study Sample: Fifteen normal-hearing listeners. Results: CS was greatest in the nonattending condition and decreased significantly when attending to the click or broadband noise suppressor. The effects of attention on CS were not frequency dependent or due to changes in recording noise measures. Conclusions: Attention to either the ipsilateral, evoking stimulus or the contralateral suppressor causes a top-down, cortically mediated release from inhibition at the level of the cochlea that is measurable with common audiologic protocols and instrumentation. Future studies assessing the effects of attention on CS of click-evoked otoacoustic emissions in normal controls and individuals with various auditory or attentional deficits may provide valuable information about the capabilities of the cortex to affect peripheral processing in a normal and/or pathological system.

Does Corticothalamic Feedback Control Cortical Velocity Tuning?

The thalamus is the major gate to the cortex, and its contribution to cortical receptive field properties is well established. Cortical feedback to the thalamus is, in turn, the anatomically dominant input to relay cells, yet its influence on thalamic processing has been difficult to interpret. For an understanding of complex sensory processing, detailed concepts of the corticothalamic interplay need to be established. To study corticogeniculate processing in a model, we draw on various physiological and anatomical data concerning the intrinsic dynamics of geniculate relay neurons, the cortical influence on relay modes, lagged and nonlagged neurons, and the structure of visual cortical receptive fields. In extensive computer simulations, we elaborate the novel hypothesis that the visual cortex controls via feedback the temporal response properties of geniculate relay cells in a way that alters the tuning of cortical cells for speed.