Patients who died were not significantly older but had higher comorbidity scores. Using patients alive at the end of the follow-up period, linear regression models were fit to the data to determine if comorbidity added more information regarding length of hospital stay than knowing only the patient's age. In the model that included only age as an independent variable, there was a significant relation between age and length of stay (F(1,303) = 5.2; P = 0.012). The R2 value for this model was 0.017. In further models that included age and each of the three comorbidity scores (separately) as the independent variables, the model that included age and the Cumulative Illness Rating Scale yielded the highest R2 value (R2 = 0.062). This study is among the first to compare three different measures of comorbidity and documents that comorbidity provides more information than knowing only the patient's age in relation to survival and length of hospital stay.

Trace eyeblink classical conditioning was assessed in patients with bilateral medial-temporal amnesia and matched control participants who had previously shown equivalent delay eyeblink conditioning (J. D. E. Gabrieli et al., 1995). The silent trace interval varied for durations of 500, 750, or 1,000 ms in successive sessions separated by at least 2 weeks; extinction trials followed each session. Patients with amnesia produced significantly fewer conditioned responses (CRs) than did control participants at all trace intervals. Both groups produced fewer CRs as the trace interval lengthened. Thus, the temporal lobe memory system in humans makes an essential contribution to normal acquisition in trace, but not delay, classical eyeblink conditioning.

The status of classical conditioning in human amnesia was examined by comparing conditioning of the eyeblink response (the unconditional response) to a tone conditioned stimulus (CS) paired with an airpuff unconditioned stimulus (US) in the delay paradigm between 7 amnesic and 7 age- and education-matched normal control participants. Amnesic patients exhibited normal baseline performance in pseudoconditioning and normal acquisition and extinction of conditioned responses in terms of the number, latency, and magnitude of eyeblinks. These results indicate that in humans, as in rabbits, brain structures critical for declarative memory are not essential for the acquisition of elementary CS-US associations.

No abstract