The Effects of learning in adult macaques as they pertain to experience-dependent suppressive plasticity , memory consolidation, and attention in the somatosensory cortex

Abstract

Over the last two decades, it has become accepted that neural responses in primary sensory areas of cortex exhibit lasting changes after learning. This study focuses on characterizing differences between the enhancing and suppressive effects of plasticity. Experience-dependent neuroplasticty causes broad increases in neural responsiveness. Suppression effects have been previously observed, but differences between the two have not been directly addressed. lV!icroelectrodes were implanted into the somatosensory cortex (Sl) of adult Rhesus macaques, and the macaques were trained to do a detection and discrimination task. After learning detection, enhancement effects were broad and nonspecific. These effects were present in neurons responsive to target input and neurons whose receptive field did not include the target site. Significant increases in receptive field size accompanied response enhancement. After learning to associate the distractor stimulus with absence of reward in discrimination, neural responses to the distractor stimulus were suppressed, and their receptive fields decreased in size. Re.sponse suppression was specific to neurons whose receptive fields received distractor input. Data collected daily in pre behavioral, behavioral, and postbehavioral sessions was compared to investigate how practice contributes to plasticity. In detection, target and control responses were significantly greater during the behavior than in pre or postbehavioral sessions. Similar effects were seen in discrimination, but behavioral responses to the distractor were not significantly elevated over their prebehavioral values. The transient. increases in spontaneous activity and evoked activity present only during the behavior may indicate attention effects. Spatial selectivity of attention effects for the target stimulus during the behavior were found to be significant. When pre behavioral data was compared with post behavioral data from the previous day, it was found that neural responses increased from the end of one behavioral session to the beginning of the neJ.."t day's session. This suggested that consolidative processes may be an important contributor to long._term plasticity. Enhancement and suppression likely operate by different mechanisms. Enhancement effects are broad and susceptible to the effects of arousal and attention. Suppression of evoked responses is specific and maintains throughout contexts in which arousal and attention are present. Consolidation is likely to be important in effecting experience-dependent. plasticity.