1. The background activity of neurones in the tritocerebrum of the locust responding to objects moved in the contralateral visual field can be influenced, possibly trans-synaptically, by electrical stimulation of the contralateral neck connective. These changes in background activity are always excitatory and may outlast the period of stimulation by several minutes. The effect of stimulating the ipsilateral cord on the discharge is weak or non-existent.

2. If the contralateral connective is shocked when the response to a moving disk has waned, the recorded cell responds to the disk again. The response continues at a high level for many presentations following stimulation of the connective. Such dishabituation does not follow stimulation of the ipsilateral neck connective.

3. Dishabituation sometimes occurs ‘spontaneously’ and cannot be accounted for as a recovery following a lapse of time.

4. Some units show diurnal variations in their responsiveness to visual stimulation.

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