Resumen de Variabilidade e repetição comportamentais apresentadas por ratos jovens e idosos

Marcia Kameyama, Maria Helena Leite Hunziker

• English

  The aim of this study was to verify the effects of aging on behavioral variability. Young (4 months) and old (20 months) rats received sucrose (20%) as a contingent reinforcement to the emission of sequences of four pressure responses to two bars, right (D) and left (E). The similarities or differences between the sequences were defined by the allocation of the D or E responses along the sequence, composing 16 possible combinations (DDEE, EDDE, etc.). Depending on the phase of the study, the reinforcement was contingent to any sequence, regardless of which bar was pressed (Lag 0), or depending on its variation (VAR) or repetition (REP) in relation to the previous. In VAR phases, the reinforcement was contingent on the emission of the sequence that differed from one, two or four last internal sequences (Lag 1, Lag 2 and Lag 4, respectively). In in REP phases, only one previously defined sequence was reinforced in 50% of emissions. In the EXT condition, no sequence was followed by reinforcement. Half of the animals (young and old) were exposed to Lag 0 - VAR - ACO - VAR - EXT contingencies and half to Lag 0 - REP - ACO - REP - EXT. Variability was measured by the U statistical index, which could occur on a continuum between 0 and 1, so that 0 indicated the maximum repetition pattern (only one kind of sequence emitted during all the session) and 1 indicated the maximum variations (emission with equal frequency of the 16 sequences throu-ghout the session). They were also recorded the response rates and percentage of reinforcement, in addition to the MetVAR index. The results were surprising in that young rats showed greater “spontaneous” variability under Lag 0 and ACO, but matched older rats under conditions where varying or repeating would produce reinforcement. Therefore, age did not interfere in the learning and maintenance of operant variability and repetition. The extension generated high rates of variation, especially in pre-REP animals. We discuss the influence of higher motor activity in young people and the preference for responses of lower “physical cost” by the elderly on the trend of differences in behavioral variability as a function of age. It is noteworthy that such differences were practically abolished when reinforcement was contingent on specific patterns of variation. These data suggest that some of the behavioral differences attributed to aging may be due to different contingencies of reinforcement available to young and elderly people.

• português

  O objetivo desse estudo foi verificar os efeitos do envelhecimento sobre a variabilidade comportamental. Ratos jovens (4 meses) e idosos (20 meses) receberam sacarose (20%) contingente à emissão de sequências de quatro respostas de pressão a duas barras. Metade dos animais foi exposta às contingências Lag 0 - VAR - ACO - VAR - EXT e metade a Lag 0 - REP - ACO - REP - EXT. Os resultados mostraram que os ratos jovens apresentaram maior variabilidade “espontânea” sob Lag 0 e ACO, porém se equipararam aos idosos nas condições em que variar ou repetir produzia reforço. Portanto, a idade não interferiu na aprendizagem e manutenção da variabilidade e repetição operantes. A extinção gerou altos índices de variação, especialmente nos animais anteriormente submetidos à REP. Discute-se a influência da atividade motora mais elevada nos jovens e a preferência por respostas de menor “custo físico” pelos idosos na determinação das diferenças de variabilidade comportamental em função da idade. Destacase que tais diferenças foram praticamente abolidas quando o reforço foi contingente a padrões específicos de variação. Esses dados sugerem que algumas das diferenças comportamentais atribuídas ao envelhecimento podem ser decorrentes das diferentes contingências de reforçamento disponíveis a ambos os grupos.