Chapter 25 molecular mechanisms of learning and memory. Declarative memories are easily formed and easily forgotten and may result from small modifications of synapses that are widely distributed. Procedural learning can be divided into 2 categories: 1) nonassociative learning, 2) associative learning. Nonassociative learning: describes the change in behavioural response that occurs over time in response to a single type of stimulus. Two types of nonassociative learning: 1) habituation: learning to ignore a stimulus that lacks meaning, 2) sensitization: learning to intensify your response to all stimuli even ones that previously evoked little or no reaction. Two types of associative learning: 1) classical conditioning: involves associating a stimulus that evokes a measurable response with a second stimulus that normally does not evoke this response. first stimulus = normally evokes response = us = meat. second stimulus = doesn t normally evoke response = cs = bell. training consists of repeated pairing sound with presentation of meat.