Olaf Christ

Automated drill-stop by SVM classified audible signals

Neuroscience research often requires direct access to brain tissue in animal models which clearly requires opening of the protective cranium. Minimizing animal numbers requests only well-experienced surgeons, since clumsy performance may lead to premature death of the animal. To minimise those traumatic outcomes, an algorithmic approach for closed-loop control of our Spherical Assistant for Stereotaxic Surgery (SASSU) was designed. Controlling the surgical robots micro-drill unit by audio pattern recognition proved to be a simple and reliable way to automatically stop the automated drill feed. Sound analysis based on the anatomical morphology of a rat skull was used to train a Support Vector Machine (SVM) classification of the time-frequency representations of the drill sound. Fully automated high throughput animal surgeries are the goal of this approach.

Estimating the spatial resolution of fNIRS sensors for BCI purposes

Differential near infrared sensors recently sparked a growing interest as a promising measuring modality for brain computer interfacing. In our study we present the design and characterization of novel, differential functional NIRS sensors, intended to record hemodynamic changes of the human motor cortex in the hand-area during motor imagery tasks. We report on the spatial characterization of a portable, multi-channel NIRS system with one module consisting of two central light emitting diodes (LED) (770 nm and 850 nm) and four symmetric pairs of radially aligned photodiodes (PD) resembling a plus symbol. The other sensor module features four similar, differential light paths crossing in the center of a star. Characterization was performed on a concentric, double beaker phantom, featuring a PBS/intralipid/blood mixture (97/1/2%). In extension of previous work, the inner, oxygenated beaker was covered by neoprene sleeves with holes of various sizes, thus giving an estimate on the spatial limits of the NIRS sensor’s measurement volume. The star shaped sensor module formed a diffuse focus of approximately 3 cm in diameter at 1.4 cm depth, whereas the plus shaped arrangement suggested a concentric ring of four separate regions of interest, overall larger than 6 cm. The systems measurement sensitivity could be improved by removing ambient light from the sensing photodiodes by optical filtering. Altogether, we conclude that both our novel fNIRS design as well as its electronics perform well in the double-layered oxygenation phantom and are thus suitable for in-vivo testing.

3D printers may reduce animal numbers to train neuroengineering procedures

Neuroengineering related interventions to small animals always carry the high risk of missled procedures, frequently causing premature death of the animal. In this paper the manufacturing process to build a physical rat skull and brain model for educational use is presented. Out of MRI images a rat brain was segmented to build a negative mould. This form was used to cast an agarose rat brain. For an accompanying rat neurocranium model, CT images were rendered to a surface mesh and printed in 3D out of PLA. The presented workflow results in a high detailed rat skull and rat brain.

When the Ostrich-Algorithm Fails: Blanking Method Affects Spike Train Statistics

Modern electroceuticals are bound to employ the usage of electrical high frequency (130–180 Hz) stimulation carried out under closed loop control, most prominent in the case of movement disorders. However, particular challenges are faced when electrical recordings of neuronal tissue are carried out during high frequency electrical stimulation, both in-vivo and in-vitro. This stimulation produces undesired artifacts and can render the recorded signal only partially useful. The extent of these artifacts is often reduced by temporarily grounding the recording input during stimulation pulses. In the following study, we quantify the effects of this method, “blanking,” on the spike count and spike train statistics. Starting from a theoretical standpoint, we calculate a loss in the absolute number of action potentials, depending on: width of the blanking window, frequency of stimulation, and intrinsic neuronal activity. These calculations were then corroborated by actual high signal to noise ratio (SNR) single cell recordings. We state that, for clinically relevant frequencies of 130 Hz (used for movement disorders) and realistic blanking windows of 2 ms, up to 27% of actual existing spikes are lost. We strongly advice cautioned use of the blanking method when spike rate quantification is attempted. Impact statement Blanking (artifact removal by temporarily grounding input), depending on recording parameters, can lead to significant spike loss. Very careful use of blanking circuits is advised.

Development of a pneumo-tactile vibrissae stimulator for freely behaving rodents

Studying rodent behavior within virtual worlds and their interaction with them is a fairly new field of research. While virtual reality is able to visually present an unlimited variety of worlds to the animal with ease, physical stimulation often remains unsatisfactory and is usually difficult to achieve. Rodents such as rats mainly experience their environment using their whiskers. Though, electrical stimulation using subcortical electrode implants have been successfully used for sensory stimulation, the underlying principles are still poorly understood. One possible and less invasive alternative method is physical stimulation of the whiskers using puffs of air with the added benefit of avoiding the overall risks of brain surgery for intracranial microstimulation.

Video tracking of swimming rodents on a reflective water surface

Abstract Animal models are an essential testbed for new devices on their path from the bench to the patient. Potential impairments by brain stimulation are often investigated in water mazes to study spatial memory and learning. Video camera based tracking systems exist to quantify rodent behaviour, but reflections of ambient lighting on the water surface and artefacts due to the waves caused by the swimming animal cause errors. This often requires tweaking of algorithms and parameters, or even potentially modifying the lab setup. In the following, we provide a simple solution to alleviate these problem using a combination of region based tracking and independent multimodal background subtraction (IMBS) without hav ing to tweak a plethora of parameters.

Prescreening seizure-like events in a rat model of epilepsy B: A 3D online video processing method

Temporal lobe epilepsy is the most common cause of drug-resistant seizures. Electrical stimulation seems to be a promising alternative to the classical anteromesial temporal resection. Our work aims at improving and validating therapeutic approaches for treating temporal lobe epilepsy using high-frequency stimulation. The relative phase clustering index (rPCI) is used to describe the epileptogenicity of a brain region and seizure prediction. An online image processing algorithm using a 3D camera is presented for facilitating the tedious and time consuming visual image inspection by traditional long term video footage required to determine optimal electrical stimulation parameters. See our companion paper describing the 2D solution in this journal.

A Remote Controlled Food Dispenser for Animal Research

Todays state of the art BMI and behavioural research usually requires an expensive recording system, which alone costs tens of thousands of euros. It is therefore desirable to cut costs elsewhere without jeopardizing the quality of the scientific outcome. Rewarding animals with food is a common practice in BMI and behavioural research. Commercially avail able laboratory food dispensers are expensive and have to be replaced frequently. Hence, our proposed design only uses a few very simple parts, which are inexpensive to fabricate. Here, we describe the design and control of these simple food dispensers.