Changes

When a taste is paired with a suspected toxin, the animal may (or may not) learn a CTA. The only way to tell if the animal has a CTA is to try to measure the CTA in an expression test (also called a retrieval test.) An expression test is also called an extinction test, because the taste is presented without the toxin: if the taste is repeatedly presented without the toxin, the animal will “unlearn” the association of taste and toxin and the CTA will be extinguished.

When a taste is paired with a suspected toxin, the animal may (or may not) learn a CTA. The only way to tell if the animal has a CTA is to try to measure the CTA in an expression test (also called a retrieval test.) An expression test is also called an extinction test, because the taste is presented without the toxin: if the taste is repeatedly presented without the toxin, the animal will “unlearn” the association of taste and toxin and the CTA will be extinguished.

=Taste reactivity (TR)=

=Taste reactivity (TR)=

one of the features of CTA is that it can change the reflexive response of the animal to a taste, i.e., the unconditioned rat responds to the taste of sucrose with ingestive orofacial movements, such as licking, tongue protrusions, and swallowing. After the rat acquires a CTA, however, it now reverses its reflexive response:  it vigourously spits out the sucrose, shakes its head, and “gapes” – the rodent equivalent to vomiting (which they are physically incapable of doing).  This change in orofacial responses can be quantified by implanting an intraoral catheter into the mouth of the rat, and videotaping the rats head as the conditioned taste is infused directly into the mouth for a brief period (30s). The behaviors of the rat are scored from the videotape frame-by-frame. If the rat has a CTA, the number of ingestive responses will decrease and the number of aversive responses increases.

One of the features of CTA is that it can change the reflexive response of the animal to a taste, i.e., the unconditioned rat responds to the taste of sucrose with ingestive orofacial movements, such as licking, tongue protrusions, and swallowing. After the rat acquires a CTA, however, it now reverses its reflexive response:  it vigourously spits out the sucrose, shakes its head, and “gapes” – the rodent equivalent to vomiting (which they are physically incapable of doing).  This change in orofacial responses can be quantified by implanting an intraoral catheter into the mouth of the rat, and videotaping the rats head as the conditioned taste is infused directly into the mouth for a brief period (30s). The behaviors of the rat are scored from the videotape frame-by-frame. If the rat has a CTA, the number of ingestive responses will decrease and the number of aversive responses increases.

The advantage of TR is that it is very precise both in terms of the stimlus presentation and the response measurement:  it measures the rats direct orofacial motor response to a fixed taste stimulus through the catheter, and it is very quantitative – the stronger the aversion, the more aversive responses. The disadvantages are that it is very labor intensive, it is not a common measure (so the historical database is not large), and it is a complicated and unnatural method of measuring a rat’s response to a taste (so there is a greater contextual influence on the learning.) Furthermore, intraoral techniques are not very sensitive: only relative strong CTAs will affect TR strongly.

The advantage of TR is that it is very precise both in terms of the stimlus presentation and the response measurement:  it measures the rats direct orofacial motor response to a fixed taste stimulus through the catheter, and it is very quantitative – the stronger the aversion, the more aversive responses. The disadvantages are that it is very labor intensive, it is not a common measure (so the historical database is not large), and it is a complicated and unnatural method of measuring a rat’s response to a taste (so there is a greater contextual influence on the learning.) Furthermore, intraoral techniques are not very sensitive: only relative strong CTAs will affect TR strongly.