[A + B] ! ucs
Inhibitory conditioning to B
Blocking, Overshadowing and Related Concepts. Fig. 6.
Blocking shown as a low percentage of baseline learning in a fear conditioning procedure. Unblocking was produced by halving the UCS (shock intensity) and was demonstrated as relatively increased percentage learning. The control level of learning was around 50%. Blocking and unblocking were affected in opposite ways by injection of opioid compounds in nucleus accumbens. (Adapted from lordanova et al. (2006b) J Neurosci 26:4036-4045, see text for full details.)
show impaired latent inhibition (though this demonstration depends on medication status). Similarly, there is good evidence for impairments in blocking in schizophrenia; hence blocking provides a potential animal model in which to assess the effects of psychoactive drugs; for example, to distinguish the role of dopamine D1 and D2 receptor families in this aspect of attentional learning, as distinct from overshadowing (Figs. 2-4). Much of this work has yet to be done, in part because reliable parameters to demonstrate blocking can be difficult to establish. An additional disadvantage in the use of blocking arises because a fully controlled study necessitates the use of an overshadowing comparison condition and overshadowing is itself affected by some of the same dopaminergic treatments. Future studies should address this confound. However, overshadowing remains of interest in its own right as a procedure to present stimuli that should normally show reduced salience for learning, to test for overcon-ditioning to weak cues in hyper-dopaminergic states (Cassaday and Moran 2010; Gray et al. 1991; Kapur 2003).
In principle, blocking has an additional attraction in that it relates an issue of fundamental importance in normal associative learning, namely the role of surprise, encapsulated in the study of prediction error. Through unblocking manipulations, we can study the liberation of attention by surprise and drug effects thereon. However, the reliable demonstration of unblocking can require extensive behavioral pilot work. Moreover, attention is only half the story in that successful associative learning should reflect the direction of change when the outcome is more or less than expected. Aficionados have noted that inhibitory learning is not consistently demonstrated in aversively motivated downshift unblocking procedures - on the contrary, a weaker UCS than expected can result in excitatory conditioning to the additional CS B (Fig. 6).
► Aminergic Hypotheses for Schizophrenia
► Animal Models for Psychiatric States
► Antipsychotic Drugs
► Attentional Bias to Drug Cues
► Classical (Pavlovian) Conditioning
► Cognitive Enhancers
► Latent Inhibition
► Schizophrenia: Animal Models
► Translational Research
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