Comparative study of environmental factors influencing motor task learning and memory retention in sighted and blind crayfish

Abstract

In classical conditioning, an alteration in response occurs when two stimuli are regularly paired in close succession. An area of particular research interest is classical conditioning with a chemical signal and visual and/or tactile stimuli as the unconditional stimuli, to test manipulative and motor behaviors in a learning paradigm. A classical learning task chamber was developed to examine learning trends in a sighted surface-dwelling crayfish, Procambarus clarkii, and in a blind cave-dwelling crayfish, Orconectes australis packardi. We examined whether learning is influenced by environmental factors and/or reliance on different primary sensory modalities. Crayfish were trained to manipulate a large, cumbersome cheliped through a small access point to obtain a food reward. In both species, acquisition of the learning task was rapid when they were in nonstressed conditions. The blind crayfish tested in low white light did not successfully complete the task, suggesting a stress response.

Keywords: Cardiac; central nervous system; crustaceans; instrumental; respiratory.

Figure 1

Schematic representation of the motor task conditioning chamber. The chamber is divided into two compartments, the larger one housing the animal and the smaller one containing a mesh platform with the food reward. Food was attached to the mesh screen. (A) A stylized angled view including the two compartments and mesh screen with worms attached. The location of the access point is indicated by the arrow. (B) Side view schematic to show placement of the mesh platform and the manipulative task of reaching in and up to obtain the food reward.

Figure 2

A graphical representation of the experimental training and testing. The light blue boxes represent exposure to the chamber and testing. The red boxes represent testing after a 4- or 7-day delay in exposure to the chamber.

Figure 3

Graphical representation of species and environmental factor comparison in a motor task. Graphs show both sighted and blind crayfish in white and red light. Sighted (white light, N = 16; red light, N = 8) and blind crayfish (white light, N = 16; red light, N = 8). The experimental procedure consisted of chamber exposure every other day continually for 3 weeks followed by a delay of 4 and 7 days (indicated by breaks in x-axis). Raw data for individual crayfish in environmental conditions are shown in (A) sighted individuals in white light, (B) blind individuals in white light, (C) sighted individuals in red light, (D) blind individuals in red light, and (E) performance index was calculated as the change in time to complete the motor task from the first day of learning and averaged across each individual. The solid line represents white light and the dotted line represents red light. ***P < 0.001 for all comparisons.

Figure 4

Graphical representation of orientation and manipulation times for both species in white and red light. (A) Sighted crayfish in white light showing individual minutes to orient and locate access point. (B) Sighted crayfish in white light showing individual minutes to manipulate the cheliped and remove reward. (C) Blind crayfish in white light showing individual minutes to orient and locate access point. (D) Blind crayfish in white light showing individual minutes to manipulate the cheliped and remove reward. (E) Sighted crayfish in red light showing individual minutes to orient and locate access point. (F) Sighted crayfish in red light showing individual minutes to manipulate the cheliped and remove reward. (G) Blind crayfish in red light showing individual minutes to orient and locate access point. (H) Blind crayfish in red light showing individual minutes to manipulate the cheliped and remove reward. (I) Orientation time only over the experiment. (J) Manipulation time. Orientation or manipulation index was calculated as the change in time from the first day of learning for each individual and then averaged across each group. Boxes indicate points of statistical comparison. ***P < 0.001 difference from Day 1. NS, no difference between groups on Day 38. The experimental procedure consisted of chamber exposure every other day continually for 3 weeks followed by a delay of 4 and 7 days (indicated by breaks in x-axis).