| << Chapter < Page | Chapter >> Page > |
Photo courtesy of Wikimedia and Andreas1.
Although the exact mechanisms are unknown, it is thought that the synaptic flexibility during formation of the hippocampus contributes to the formation and retention of memories (Leurner, 2006). Hippocampal activity has been shown to differ between males and females, particularly in rodent species.
In a wide range of mammals, the dentate gyrus in the adult hippocampus produces a large number of new neurons in a process called neurogenesis (Leurner, 2006). This production is reduced by stressful experiences such as predator scents, social dominance, maternal deprivation, and mild foot-shocks (Shors, 2007).
Because treatment with antidepressants, such as Prozac (fluoxetine), increases neurogenesis in the hippocampus (Shors, 2007) and the volume of the hippocampus is less in depressed patients relative to normal patients (Neumeister, 2005) it is believed that the hippocampus is directly related to depression and learned helplessness.
Learned helplessness is one way animals express depression. Shors et al (2007) studied the connection between neurogenesis and learned helplessness in the rat model. They found that in males, but not females, the ability to control the stress increased hippocampal activity and thus reduced helplessness behavior.
Operant conditioning occurs when an animal must make a deliberate response in order to learn. Usually, they learn to avoid a stimulus such as the foot shock discussed in the previous section. Dalla and colleagues (2008) used a one-way avoidance task where rats had to pass through a doorway once to avoid shock. Although rats are able to learn this task on the first day of training, females learned to escape sooner than males (Dalla, 2008).
Shores et al (2007) used the same one-way avoidance task to test hippocampal activity (see [link] ) and learned helplessness in rats. Two groups of rats were placed in shock-chambers in which one group could escape and avoid the foot-shock (controllable stress group) and one group could escape but could not avoid the foot-shock (uncontrollable stress group). Both groups were then put in new chambers where escape was possible. In this new learning situation, male and female rats that were previously in the controllable stress group were able to learn to avoid the foot-shock quickly. For those previously in the uncontrollable stress group, however, male rats expressed learned helplessness more frequently than females (Shores, 2007). Learned helplessness is a behavior that occurs when an individual is places under uncontrollable stress and learns that escape is not possible. Thus in new learning tasks they move less and either take longer to learn to escape or cannot learn to escape at all (Shores, 2006). This type of behavior, then, is associated with an inability to learn future tasks that require movement.
Notification Switch
Would you like to follow the 'Mockingbird tales: readings in animal behavior' conversation and receive update notifications?
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|