Mapping of the auditory area in the cerebellar vermis and hemispheres of the mustache bat, Pteronotus parnellii parnellii

Dissociation between Cerebellar and Cerebral Neural Activities in Humans with Long-Term Bilateral Sensorineural Hearing Loss

Abnormal neural activity in the cerebellum has been implicated in hearing impairments, but the effects of long-term hearing loss on cerebellar function are poorly understood. To further explore the role of long-term bilateral sensorineural hearing loss on cerebellar function, we investigated hearing loss-induced changes among neural networks within cerebellar subregions and the changes in cerebellar-cerebral connectivity patterns using resting-state functional MRI. Twenty-one subjects with long-term bilateral moderate-to-severe sensorineural hearing loss and 21 matched controls with clinically normal hearing underwent MRI scanning and a series of neuropsychological tests targeting cognition and emotion. Voxel-wise functional connectivity (FC) analysis demonstrated decreased couplings between the cerebellum and other cerebral areas, including the temporal pole (TP), insula, supramarginal gyrus, inferior frontal gyrus (IFG), medial frontal gyrus, and thalamus, in long-term bilateral sensorineural hearing loss patients. An ROI-wise FC analysis found weakened interregional connections within cerebellar subdivisions. Moreover, there was a negative correlation between anxiety and FC between the left cerebellar lobe VI and left insula. Hearing ability and anxiety scores were also correlated with FC between the left cerebellar lobe VI and left TP, as well as the right cerebellar lobule VI and left IFG. Our results suggest that sensorineural hearing loss disrupts cerebellar-cerebral circuits, some potentially linked to anxiety, and interregional cerebellar connectivity. The findings contribute to a growing body showing that auditory deprivation caused by cochlear hearing loss disrupts not only activity with the classical auditory pathway but also portions of the cerebellum that communicates with other cortical networks.

Purkinje cell compartmentation of the cerebellum of microchiropteran bats

Transverse boundaries divide the mammalian cerebellar cortex into transverse zones, and within each zone the cortex is further subdivided into a symmetrical array of parasagittal stripes. This topography is highly conserved across the Mammalia. Bats have a remarkable cerebellum with presumed adaptations to flight and to echolocation, but nothing is known of its compartmentation. We have therefore used two Purkinje cell compartmentation antigens, zebrin II/aldolase C and phospholipase Cbeta4, to reveal the topography of the cerebellum in microchiropteran bats. Three species of bat were studied, Lasiurus cinereus, Lasionycteris noctivagans, and Eptesicus fuscus. A reproducible pattern of zones and stripes was revealed that is similar across the three species. The architecture of the bat cerebellum conforms to the ground plan of other mammals. However, two exceptions to the highly conserved mammalian architectural plan were revealed. First, many Purkinje cells in lobule I express zebrin II. A zebrin II-immunopositive lobule I has not been seen previously in mammals but is characteristic of the avian cerebellum. Second, lobules VI-VII comprise the large central zone. Within the central zone two subdomains are evident, a small anterior subdomain (lobule VI) in which Purkinje cells are predominantly zebrin II-immunopositive/PLCbeta4-immunonegative, as in other mammals, and a posterior subdomain (lobule VII), in which alternating zebrin II/phospholipase Cbeta4 stripes are prominent.

Cerebellum and auditory function: an ALE meta-analysis of functional neuroimaging studies

Over the past two decades neuroimaging data have accumulated showing that the cerebellum, traditionally viewed only as a motor structure, is also active in a wide variety of sensory and cognitive tasks. We have proposed that instead of explicit involvement in any particular motor, sensory, or cognitive task, the cerebellum performs a much more fundamental computation involving the active acquisition of sensory data. We carried out an activation likelihood estimate (ALE) meta-analysis to determine whether neuroimaging results obtained during a wide range of auditory tasks support this proposal. Specifically, we analyzed the coordinates of 231 activation foci obtained in 15 different auditory studies selected through an extensive search of the positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) literature. The studies selected represent a wide variety of purely auditory tasks using highly controlled synthesized acoustic stimuli. The results clearly revealed that in addition to temporal auditory areas of cerebral cortex, specific regions in the cerebellum are activated consistently across studies regardless of the particular auditory task involved. In particular, one area in left lateral crus I area showed the greatest volume and ALE peak value among the extratemporal regions. A subanalysis was carried out that ruled out the specific association of this cerebellar cluster with attentional demand. The results are consistent with the hypothesis that the cerebellum may play a role in purely sensory auditory processing, and are discussed in light of the broader idea of the cerebellum subserving a fundamental sensory function.

Auditory Pontine Grey: Connections and Response Properties in the Horseshoe Bat

This study investigates the role of the pontine grey as a link between the auditory system and the cerebellum in the bat, Rhinolophus rouxi. We recorded response properties of single neurons in the pontine grey and, in the same preparation, injected wheat germ agglutinin - horseradish peroxidase (WGA - HRP) in areas responsive to sound. Thus the functional evidence was correlated with retrograde and anterograde transport. The main results are: (i) all auditory neurons in the pontine grey are tuned within one of two harmonically related frequency ranges of the echolocation call. The upper range corresponds to the constant frequency and frequency modulated components of the second harmonic, but the lower range corresponds only to the frequency modulated component of the first harmonic. There is no systematic tonotopic organization; (ii) discharge patterns are extremely variable, latencies cover a wide range, and about half of the neurons are binaurally responsive with excitation from both ears; (iii) most pontine auditory neurons respond preferentially to frequency modulated stimuli; (iv) there is massive input to the pontine grey from the central nucleus of the inferior colliculus; (v) cortical input to the pontine grey does not originate in tonotopically organized auditory cortex. The input is from a dorsal belt area that is specialized for processing combinations of sounds with specific frequency ratios and delays; (vi) projections from the auditory region of the pontine grey are widespread within the cerebellar cortex. The data suggest that the pontine grey transmits to the cerebellum information contained in specific components of the bat's biosonar signal.

Frequency and space representation in the primary auditory cortex of the frequency modulating bat Eptesicus fuscus

1. Frequency and space representation in the auditory cortex of the big brown bat, Eptesicus fuscus, were studied by recording responses of 223 neurons to acoustic stimuli presented in the bat's frontal auditory space. 2. The majority of the auditory cortical neurons were recorded at a depth of less than 500 microns with a response latency between 8 and 20 ms. They generally discharged phasically and had nonmonotonic intensity-rate functions. The minimum threshold, (MT) of these neurons was between 8 and 82 dB sound pressure level (SPL). Half of the cortical neurons showed spontaneous activity. All 55 threshold curves are V-shaped and can be described as broad, intermediate, or narrow. 3. Auditory cortical neurons are tonotopically organized along the anteroposterior axis of the auditory cortex. High-frequency-sensitive neurons are located anteriorly and low-frequency-sensitive neurons posteriorly. An overwhelming majority of neurons were sensitive to a frequency range between 30 and 75 kHz. 4. When a sound was delivered from the response center of a neuron on the bat's frontal auditory space, the neuron had its lowest MT. When the stimulus amplitude was increased above the MT, the neuron responded to sound delivered within a defined spatial area. The response center was not always at the geometric center of the spatial response area. The latter also expanded with stimulus amplitude. High-frequency-sensitive neurons tended to have smaller spatial response areas than low-frequency-sensitive neurons. 5. Response centers of all 223 neurons were located between 0 degrees and 50 degrees in azimuth, 2 degrees up and 25 degrees down in elevation of the contralateral frontal auditory space. Response centers of auditory cortical neurons tended to move toward the midline and slightly downward with increasing best frequency. 6. Auditory space representation appears to be systematically arranged according to the tonotopic axis of the auditory cortex. Thus, the lateral space is represented posteriorly and the middle space anteriorly. Space representation, however, is less systematic in the vertical direction. 7. Auditory cortical neurons are columnarly organized. Thus, the BFs, MTs, threshold curves, azimuthal location of response centers, and auditory spatial response areas of neurons sequentially isolated from an orthogonal electrode penetration are similar.

Auditory spatial response areas of single neurons and space representation in the cerebellum of echo locating bats

Using free-field acoustic stimulation conditions, we studied the auditory spatial response areas of 242 cerebellar neurons of Eptesicus fuscus. A best frequency stimulus was delivered from a loudspeaker which was moved across the frontal auditory space in order to determine the response center of each cerebellar neuron. At the response center, the neuron had its lowest minimum threshold. The stimulus was then raised 5-15 dB above the lowest minimum threshold of each neuron and the spatial response area for each stimulus intensity was measured. The spatial response area of each neuron expanded asymmetrically with the stimulus intensity. The size of the spatial response area was not correlated with the minimum threshold, best frequency or recording depth of the neuron. The distribution of the best frequencies of single neurons was not correlated with their recording depths or minimum thresholds. The response centers of all cerebellar neurons were located within a small area of the central portion of the frontal auditory space suggesting that the cerebellum could play an effective role in orienting the bat toward the echo source within the frontal gaze during insect capture.