Acquisition of a High-precision Skilled Forelimb Reaching Task in Rats

Summary

A paradigm is presented to analyze the acquisition of a high-precision skilled forelimb reaching task in rats.

Abstract

Movements are the main measurable output of central nervous system function. Developing behavioral paradigms that allow detailed analysis of motor learning and execution is of critical importance in order to understand the principles and processes that underlie motor function. Here we present a paradigm to study movement acquisition within a daily session of training (within-session) representing the fast learning component and primary acquisition as well as skilled motor learning over several training sessions (between-session) representing the slow learning component and consolidation of the learned task. This behavioral paradigm increases the degree of difficulty and complexity of the motor skill task due to two features: First, the animal realigns its body prior to each pellet retrieval forcing renewed orientation and preventing movement execution from the same angle. Second, pellets are grasped from a vertical post that matches the diameter of the pellet and is placed in front of the cage. This requires a precise grasp for successful pellet retrieval and thus prevents simple pulling of the pellet towards the animal. In combination with novel genetics, imaging and electrophysiological technologies, this behavioral method will aid to understand the morphological, anatomical and molecular underpinnings of motor learning and memory.

Introduction

Movement control is a core function of the central nervous system (CNS). Motricity is the main measurable output of CNS function and the main possibility for individuals to interact with the external world. Understanding the principles of motor function and the mechanisms that underlie the learning of a motor task is currently one of the big challenges in neuroscience. Morphological, physiological and molecular changes were found upon acquisition of a new motor task. For example, the shape and number of synapses change in response to skilled motor training^1-5, and functional changes of the synaptic machinery were observed after motor learning. Synaptic resp....

Protocol

All experiments were performed in accordance with the guidelines of the Veterinary Office of the Canton Zurich, Switzerland.

1. Animal Handling and Habituation

1. Animal Handling
   Note: 5 days prior to the start of the experiment, perform step 1.1.1 daily.
   1. For behavioral experiments, accustom the animals to the experimenter. Have daily handling sessions lasting 10-15 min per animal. Clean the box after each animal’s session.
      1. Initially, place the experimenter’s hand into a cage allowing the animal to explore and smell to become familiarized with the experimenter.
      <....

Results

Successful motor skill acquisition is only achieved through consistent practice. Despite careful consideration of all aspects, some rats fail to learn the task (Figure 2). These 'non-learners' either lack motivation resulting in few or absent attempts of pellet retrieval from the start of the experiment or generally lose interest in reaching for the pellets leading to continuously failed attempts. By contrast, some animals show aggressive and over-motivated behavior resulting in overhasty and rushed gras.......

Discussion

The paradigm shown in this study is adapted from Buitrago et al.¹⁸ and differs from the classical single pellet reaching paradigm¹⁷ mainly in two aspects:

First, studying within-session improvement allows analysis of the learned task within a single day, which can provide a different level of information such as investigation of the fast learning component compared to the slow learning component represented by the average daily values (see Figures 3

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Training box			Self Made
Pedestal			Self Made
Sugar pellets	TSE Systems Intl. Group		45 mg dustless precision pellets
Sprague Dawley rats			5-6 week old males
Laptop computer	Hewlett Packard
Stop Watch
Forceps	Fine Science Tools (FST)
Excel	Microsoft
Prism	GraphPad
Weighing scale
Counter