Poster summarising dissertation entitled "Classical Conditioning and Latent Inhibition in Planarian Flatworms" by Kate Stewart.

2. It has been linked to attentional dysfunctions: schizophrenics do not filter the information coming from the environment, which results in the cognitive style characteristic of the disorder.

3. Learning phenomena that require the usage of an attentional filter, like latent inhibition (Lubow, 1989) and blocking (Kamin (1969), have been successfully used as models for Schizophrenia.

4. In latent inhibition, the attention system filters the information coming from familiar stimuli, which then cannot acquire the properties of an effective conditioned stimulus.

5. Schizophrenics are known to be refractory to latent inhibition (e.g., Baruch, Hemsley, & Gray, 1988). This has led to research on mammals (mainly rats) to model schizophrenia and investigate new pharmacological treatments.

6. We aim to develop an invertebrate model that can be used instead of mammals in pre-psychiatric research of schizophrenia.1 2 Experiment 1 Objective: to produce a clear demonstration of conditioning in planarian that cannot be attributed to sensitization. Group ExperimentalGroup Control Light  Shock Light / Shock (at random) Experiment 2 Objective: to produce a clear demonstration of latent inhibition in planarian. Experimental animals were exposed to the light. Group ExperimentalGroup Control Light (x30) Light Shock ------- Light Shock 3 Results The conditioned response (CR): longitudinal contraction or sudden turning (respon-ses) elicited by the shock unconditioned stimulus (US). All the conditioning trials were videotaped and the responses registered by two independent observers. 4 5 Experiment 1: Animals in Group Experimental learned to use the light as a signal for the shock-US. Given that all the animals were exposed to the shock US, the development of the conditioned response in Group Experimental cannot be attributed to sensitization. View from above Experiment 1 Experiment 2 Experiment 2: Animals in Group Experimental (worms that were rendered fully fami-liar with the light before conditioningthananimals in Group ) took longer to learn to predict the shock in the presence of the light Control (which had never experienced the light before conditioning). This can be taken to be a demonstration of the latent inhibition effect in planarian worms. Schematic representation of our experimental setting The experiments reported succeeded in demonstrating Pavlovian conditioning and latent inhibition in planarian worms. Our future research will assess whether the equivalence between latent inhibition in invertebrates and mammals is merely functional or structural. If, for example, latent inhibition is affected by amphetamine (as it has been shown to be in mammals), the gate would open for research of the molecular bases of schizophrenia in planarian worms, and new antipsychotic drugs could be confidently tested in invertebrates. 6 E-mail (Leicester): jpg19@le.ac.uk (Jose Prados); E-mail (London): cdavidso@sgul.ac.uk (Colin Davidson)