1. Describe the organization of the insect Antennal Lobe. Your answer should include the general anatomy, what types of cells are present and how they are connected. [8]
AL is made up of many Glomeruli [1]
Olfactory receptor neurons [1]; project in from antenna [1]; many types [0.5]; all of one type go to the same part of the AL (=Glomerulus) [1]; connect to Local neurons [1]
Local neurons [1]; connection all within AL [1]; connect with Projection neurons [1]; some connection within their glomerulus [0.5]; some connections to other glomeruli [0.5]; inhibitory connections with PNs [1]
Projection neurons [1]; project from AL to other brain regions (e.g. Mushroom Body) [1]
- What is the optomotor response? [2]
visual reflex [1];
response to large-field visual motion [1];
tendency to move in same direction as motion stimulus [1];
stabilizes visual pattern on retina [1]
3.
a) What are two visual cues that characterize looming objects (ie objects on a collision course)?
b) How does the locust LGMD neuron respond to these? Assume the object approaches with a constant velocity.
[6]
a)expanding image size [1]; accelerating [1] edge movement [1];
b)excitatory response to edge movement [1]; non-adapting if edges are accelerating; inhibitory response increasing image size [1] (at least for images larger than optimal size [1]); as the object approaches the excitatory effect of edge movement increases [1]; inhibitory effect of increasing image size also increases as object gets closer [1];
4. What is the basis of odotopic activity in the insect antennal lobe? [2]
- olfactory receptor cells with similar sensitivity project to the same glomerulus (plural = glomeruli) in the antennal lobe
- one odour will activate one type of receptor, and therefore one region (glomerulus) of antennal lobe
- The figures below show results of experiments in which honey bees were first trained to a food source located half way down a tunnel 20m long and 14cm wide. The figures show the relative frequency of bees searching at different di-stances along the tunnel after the food source is removed. The graph on the left shows the results of training the bees using a tunnel with either a vertical stripe pattern (stripes) or a random pattern (random texture). The graph on the right shows the frequency of searching at different distances along the tunnel for bees trained with a random pattern and then tested with either vertical stripes or axial stripes (ie oriented with the long axis of the tunnel). The inverted triangle in each graph indicates the location of the food source (reward) during training. What do these results suggest about the perception of distance in honey bees? [10]
-bees are able to learn the location in the tunnel [1], after finding food at one location in the tunnel bees search near the same location when there is no food [1] indicating that they have some way of recognizing how far down the tunnel they have travelled [1]
-they learn this equally well for different patterns (stripes, random) [1]
-the bees are equally accurate when the pattern is changed from random during training to vertical stripes during testing [1]
-they are unable to find the correct location if the pattern is changed from random pattern to axial stripes [1]
-these results suggest that the bees’ estimate of distance is based on the perception of visual motion [1] because the axial stripe pattern is the only one that does not generate visual motion cues when the bees fly through the tunnel [1]
-their distance estimate is independent of the spatial scale of the pattern [1] (so it’s different from the optomotor response [1])