During the processing of information in humans, activated neurons behave in a specific way. The activity of these neurons leaves traces on the neurons, such as changes in synaptic or intrinsic properties. Formation of the memory traces is associated with molecular changes in the neurons. Hence, monitoring collective neural activities and following the trace of neural activities are important to neuroscience research. This collective or group of neurons is described as a 'neural ensemble', while the neural trace is described as a 'neural engram'. Both terms have been used and studied by neuroscientists for a long time. In this article, we discuss the development of these concepts, current research methods, and future areas of development.