Impact of enriched environment on motor performance and learning in mice

Neuroscience heavily relies on animal welfare in laboratory rodents as it can significantly affect brain development, cognitive function and memory formation. Unfortunately, laboratory animals are often raised in artificial environments devoid of physical and social stimuli, potentially leading to biased outcomes in behavioural assays. To assess this effect, we examined the impact of social and physical cage enrichment on various forms of motor coordination. Our findings indicate that while enriched-housed animals did not exhibit faster learning in eyeblink conditioning, the peak timing of their conditioned responses was slightly, but significantly, improved. Additionally, enriched-housed animals outperformed animals that were housed in standard conditions in the accelerating rotarod and ErasmusLadder test. In contrast, we found no significant effect of enrichment on the balance beam and grip strength test. Overall, our data suggest that an enriched environment can improve motor performance and motor learning under challenging and/or novel circumstances, possibly reflecting an altered state of anxiety.

Accessible and reliable neurometric testing in humans using a smartphone platform

Tests of human brain circuit function typically require fixed equipment in lab environments. We have developed a smartphone-based platform for neurometric testing. This platform, which uses AI models like computer vision, is optimized for at-home use and produces reproducible, robust results on a battery of tests, including eyeblink conditioning, prepulse inhibition of acoustic startle response, and startle habituation. This approach provides a scalable, universal resource for quantitative assays of central nervous system function.

Human brain mapping using co-registered fUS, fMRI and ESM during awake brain surgeries: A proof-of-concept study

Accurate, depth-resolved functional imaging is key in both understanding and treatment of the human brain. A new sonography-based imaging technique named functional Ultrasound (fUS) uniquely combines high sensitivity with submillimeter-subsecond spatiotemporal resolution available in large fields-of-view. In this proof-of-concept study we show that: (A) fUS reveals the same eloquent regions as found by fMRI while concomitantly visualizing in-vivo microvascular morphology underlying these functional hemodynamics and (B) fUS-based functional maps are confirmed by Electrocortical Stimulation Mapping (ESM), the current gold-standard in awake neurosurgical practice. This unique cross-modality experiment was performed using motor, visual and language-related functional tasks in patients undergoing awake brain tumor resection. The current work serves as an important milestone towards further maturity of fUS as well as a novel avenue to increase our understanding of hemodynamics-based functional brain imaging.

Cerebellum-dependent associative learning is not impaired in a mouse model of neurofibromatosis type 1

Individuals with Neurofibromatosis type 1 (NF1) experience a high degree of motor problems. The cerebellum plays a pivotal role in motor functioning and the NF1 gene is highly expressed in cerebellar Purkinje cells. However, it is not well understood to what extent NF1 affects cerebellar functioning and how this relates to NF1 motor functioning. Therefore, we subjected global Nf1^+/- mice to a cerebellum-dependent associative learning task, called Pavlovian eyeblink conditioning. Additionally, we assessed general motor function and muscle strength in Nf1^+/- mice. To our surprise, we found that Nf1^+/- mice showed a moderately increased learning rate of conditioned eyeblink responses, as well as improved accuracy in the adaptive timing of the eyeblink responses. Locomotion, balance, general motor function, and muscle strength were not affected in Nf1^+/- mice. Together, our results support the view that cerebellar function in Nf1^+/- mice is unimpaired.

P09.03 Fully integrating functional Ultrasound (fUS) into the onco-neurosurgical operating room: Towards a new real-time, high-resolution image-guided resection tool with multimodal potential

BACKGROUND

Onco-neurosurgical practice still relies heavily on pre-operatively acquired images to guide intra-operative decision-making for safe tumor removal, a practice with inherent pitfalls such as registration inaccuracy due to brain shift, and lack of real-time (functional) feedback. Exploiting the opportunity for real-time imaging of the exposed brain can improve intra-operative decision-making, neurosurgical safety and patient outcomes. Previously, we described functional Ultrasound (fUS) as a high-resolution, depth-resolved imaging technique able to detect functional regions and vascular morphology during awake resections. Here, we present for the first time fUS as a fully integrated, MRI/CT-registered imaging modality in the OR.

MATERIAL AND METHODS

fUS relies on high-frame-rate (HFR) ultrasound, making the technique sensitive for very small motions caused by vascular dynamics (µDoppler) and allowing measurements of changes in cerebral blood volume (CBV) with micrometer-millisecond precision. This opens up the possibility to 1) detect functional response, as CBV-changes reflect changes in metabolism of activated neurons through neurovascular coupling and 2) visualize in-vivo vascular morphology of tumor and healthy tissue. During a range of anesthetized and awake onco-neurosurgical procedures we acquired images of brain and spinal cord using conventional linear ultrasound probes connected to an experimental acquisition unit. Building on Brainlab’s ‘Cranial Navigation’ and ‘Intra-Operative Ultrasound’ modules, we could co-register our intra-operative Power Doppler Images (PDIs) to patient-registered MRI/CT-data. Using the ‘IGTLink’ research interface, we could access and store real-time tracking data for informed volume reconstructions in post-processing.

RESULTS

Intra-operative fUS could be registered to MRI/CT-images in real-time, showing overlays of PDIs at imaging depths of >5 centimeters. During meningioma resections, these co-registered PDIs revealed fUS’ ability to visualize the tumor’s feeding vessels and surrounding healthy vasculature prior to durotomy, with a level of detail unprecedented by conventional MRI-sequences. Comparing post-operatively reconstructed 3D-vascular maps of pre- and post-durotomy acquisitions, further confirmed the dural dependency of the vascular network feeding the tumor. During awake resections, fUS revealed distinct functional areas as activated during motor and language tasks.

CONCLUSION

fUS is a new real-time, high-resolution and depth-resolved imaging technique, combining characteristics uniquely beneficial for a potential image-guided resection tool. The successful integration of fUS in the onco-neurosurgical OR demonstrated by our team, is an essential step towards clinical integration of fUS, as well as the technique’s validation against modalities such as MRI and CT.

High frequency switched-mode stimulation can evoke post synaptic responses in cerebellar principal neurons

This paper investigates the efficacy of high frequency switched-mode neural stimulation. Instead of using a constant stimulation amplitude, the stimulus is switched on and off repeatedly with a high frequency (up to 100 kHz) duty cycled signal. By means of tissue modeling that includes the dynamic properties of both the tissue material as well as the axon membrane, it is first shown that switched-mode stimulation depolarizes the cell membrane in a similar way as classical constant amplitude stimulation. These findings are subsequently verified using in vitro experiments in which the response of a Purkinje cell is measured due to a stimulation signal in the molecular layer of the cerebellum of a mouse. For this purpose a stimulator circuit is developed that is able to produce a monophasic high frequency switched-mode stimulation signal. The results confirm the modeling by showing that switched-mode stimulation is able to induce similar responses in the Purkinje cell as classical stimulation using a constant current source. This conclusion opens up possibilities for novel stimulation designs that can improve the performance of the stimulator circuitry. Care has to be taken to avoid losses in the system due to the higher operating frequency.

The effect of an mGluR5 inhibitor on procedural memory and avoidance discrimination impairments in Fmr1 KO mice

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability. Patients with FXS do not only suffer from cognitive problems, but also from abnormalities/deficits in procedural memory formation. It has been proposed that a lack of fragile X mental retardation protein (FMRP) leads to altered long-term plasticity by deregulation of various translational processes at the synapses, and that part of these impairments might be rescued by the inhibition of type I metabotropic glutamate receptors (mGluRs). We recently developed the Erasmus Ladder, which allows us to test, without any invasive approaches, simultaneously, both procedural memory formation and avoidance behavior during unperturbed and perturbed locomotion in mice. Here, we investigated the impact of a potent and selective mGluR5 inhibitor (Fenobam) on the behavior of Fmr1 KO mice during the Erasmus Ladder task. Fmr1 KO mice showed deficits in associative motor learning as well as avoidance behavior, both of which were rescued by intraperitoneal administration of Fenobam. While the Fmr1 KO mice did benefit from the treatment, control littermates suffered from a significant negative side effect in that their motor learning skills, but not their avoidance behavior, were significantly affected. On the basis of these studies in the FXS animal model, it may be worthwhile to investigate the effects of mGluR inhibitors on both the cognitive functions and procedural skills in FXS patients. However, the use of mGluR inhibitors appears to be strongly contraindicated in healthy controls or non-FXS patients with intellectual disability.

Timing in the cerebellum: oscillations and resonance in the granular layer

The brain generates many rhythmic activities, and the olivo-cerebellar system is not an exception. In recent years, the cerebellum has revealed activities ranging from low frequency to very high-frequency oscillations. These rhythms depend on the brain functional state and are typical of certain circuit sections or specific neurons. Interestingly, the granular layer, which gates sensorimotor and cognitive signals to the cerebellar cortex, can also sustain low frequency (7-25 Hz) and perhaps higher-frequency oscillations. In this review we have considered (i) how these oscillations are generated in the granular layer network depending on intrinsic electroresponsiveness and circuit connections, (ii) how these oscillations are correlated with those in other cerebellar circuit sections, and (iii) how the oscillating cerebellum communicates with extracerebellar structures. It is suggested that the granular layer can generate oscillations that integrate well with those generated in the inferior olive, in deep-cerebellar nuclei and in Purkinje cells. These rhythms, in turn, might play a role in cognition and memory consolidation by interacting with the mechanisms of long-term synaptic plasticity.

Savings and extinction of conditioned eyeblink responses in fragile X syndrome

The fragile X syndrome (FRAXA) is the most widespread heritable form of mental retardation caused by the lack of expression of the fragile X mental retardation protein (FMRP). This lack has been related to deficits in cerebellum-mediated acquisition of conditioned eyelid responses in individuals with FRAXA. In the present behavioral study, long-term effects of deficiency of FMRP were investigated by examining the acquisition, savings and extinction of delay eyeblink conditioning in male individuals with FRAXA. In the acquisition experiment, subjects with FRAXA displayed a significantly poor performance compared with controls. In the savings experiment performed at least 6 months later, subjects with FRAXA and controls showed similar levels of savings of conditioned responses. Subsequently, extinction was faster in subjects with FRAXA than in controls. These findings confirm that absence of the FMRP affects cerebellar motor learning. The normal performance in the savings experiment and aberrant performance in the acquisition and extinction experiments of individuals with FRAXA suggest that different mechanisms underlie acquisition, savings and extinction of cerebellar motor learning.

Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome

Williams Syndrome (WS, [MIM 194050]) is a disorder caused by a hemizygous deletion of 25-30 genes on chromosome 7q11.23. Several of these genes including those encoding cytoplasmic linker protein-115 (CYLN2) and general transcription factors (GTF2I and GTF2IRD1) are expressed in the brain and may contribute to the distinct neurological and cognitive deficits in WS patients. Recent studies of patients with partial deletions indicate that hemizygosity of GTF2I probably contributes to mental retardation in WS. Here we investigate whether CYLN2 and GTF2IRD1 contribute to the motoric and cognitive deficits in WS. Behavioral assessment of a new patient in which STX1A and LIMK1, but not CYLN2 and GTF2IRD1, are deleted showed that his cognitive and motor coordination functions were significantly better than in typical WS patients. Comparative analyses of gene specific CYLN2 and GTF2IRD1 knockout mice showed that a reduced size of the corpus callosum as well as deficits in motor coordination and hippocampal memory formation may be attributed to a deletion of CYLN2, while increased ventricle volume can be attributed to both CYLN2 and GTF2IRD1. We conclude that the motor and cognitive deficits in Williams Syndrome are caused by a variety of genes and that heterozygous deletion of CYLN2 is one of the major causes responsible for such dysfunctions.

Deletion of FMR1 in Purkinje Cells Enhances Parallel Fiber LTD, Enlarges Spines, and Attenuates Cerebellar Eyelid Conditioning in Fragile X Syndrome

Absence of functional FMRP causes Fragile X syndrome. Abnormalities in synaptic processes in the cerebral cortex and hippocampus contribute to cognitive deficits in Fragile X patients. So far, the potential roles of cerebellar deficits have not been investigated. Here, we demonstrate that both global and Purkinje cell-specific knockouts of Fmr1 show deficits in classical delay eye-blink conditioning in that the percentage of conditioned responses as well as their peak amplitude and peak velocity are reduced. Purkinje cells of these mice show elongated spines and enhanced LTD induction at the parallel fiber synapses that innervate these spines. Moreover, Fragile X patients display the same cerebellar deficits in eye-blink conditioning as the mutant mice. These data indicate that a lack of FMRP leads to cerebellar deficits at both the cellular and behavioral levels and raise the possibility that cerebellar dysfunctions can contribute to motor learning deficits in Fragile X patients.

Cerebellar LTD and learning-dependent timing of conditioned eyelid responses

Mammals can be trained to make a conditioned movement at a precise time, which is correlated to the interval between the conditioned stimulus and unconditioned stimulus during the learning. This learning-dependent timing has been shown to depend on an intact cerebellar cortex, but which cellular process is responsible for this form of learning remains to be demonstrated. Here, we show that protein kinase C-dependent long-term depression in Purkinje cells is necessary for learning-dependent timing of Pavlovian-conditioned eyeblink responses.

Analysis of Cx36 knockout does not support tenet that olivary gap junctions are required for complex spike synchronization and normal motor performance

Electrotonic coupling by gap junctions between neurons in the inferior olive has been claimed to underly complex spike (CS) synchrony of Purkinje cells in the cerebellar cortex and thereby to play a role in the coordination of movements. Here, we investigated the motor performance of mice that lack connexin36 (Cx36), which appears necessary for functional olivary gap junctions. Cx36 null-mutants are not ataxic, they show a normal performance on the accelerating rotorod, and they have a regular walking pattern. In addition, they show normal compensatory eye movements during sinusoidal visual and/or vestibular stimulation. To find out whether the normal motor performance in mutants reflects normal CS activity or some compensatory mechanism downstream of the cerebellar cortex, we determined the CS firing rate, climbing-fiber pause, and degree of CS synchrony. None of these parameters in the mutants differed from those in wildtype littermates. Finally, we investigated whether the role of coupling becomes apparent under challenging conditions, such as during application of the tremorgenic drug harmaline, which specifically turns olivary neurons into an oscillatory state at a high frequency. In both the mutants and wildtypes this application induced tremors of a similar duration with similar peak frequencies and amplitudes. Thus surprisingly, the present data does not support the notion that electrotonic coupling by gap junctions underlies synchronization of olivary spike activity and that these gap junctions are essential for normal motor performance.

Monitoring kinetic and frequency-domain properties of eyelid responses in mice with magnetic distance measurement technique

Classical eye-blink conditioning in mutant mice can be used to study the molecular mechanisms underlying associative learning. To measure the kinetic and frequency domain properties of conditioned (tone - periorbital shock procedure) and unconditioned eyelid responses in freely moving mice, we developed a method that allows adequate, absolute, and continuous determination of their eyelid movements in time and space while using an electrical shock as the unconditioned stimulus. The basic principle is to generate a local magnetic field that moves with the animal and that is picked up by either a field-sensitive chip or coil. With the use of this magnetic distance measurement technique (MDMT), but not with the use of electromyographic recordings, we were able to measure mean latency, peak amplitude, velocity, and acceleration of unconditioned eyelid responses, which equaled 7.9 +/- 0.2 ms, 1.2 +/- 0.02 mm, 28.5 +/- 1 mm/s, and 637 +/- 22 mm/s(2), respectively (means +/- SD). During conditioning, the mice reached an average of 78% of conditioned responses over four training sessions, while animals that were subjected to randomly paired conditioned and unconditioned stimuli showed no significant increases. The mean latency of the conditioned responses decreased from 222 +/- 40 ms in session 2 to 127 +/- 6 ms in session 4, while their mean peak latency increased from 321 +/- 45 to 416 +/- 67 ms. The mean peak amplitudes, peak velocities, and peak acceleration of these responses increased from 0.62 +/- 0.02 to 0.77 +/- 0.02 mm, from 3.9 +/- 0.3 to 7.7 +/- 0.5 mm/s, and from 81 +/- 7 to 139 +/- 10 mm/s(2), respectively. Power spectra of acceleration records illustrated that both the unconditioned and conditioned responses of mice had oscillatory properties with a dominant peak frequency close to 25 Hz that was not dependent on training session, interstimulus interval, or response size. These data show that MDMT can be used to measure the kinetics and frequency domain properties of conditioned eyelid responses in mice and that these properties follow the dynamic characteristics of other mammals.