Certain chemicals induce neuromodulation.
A suburb is a residential area or a mixed use area , either existing as part of a city or urban area or as a separate residential community within commuting distance of a city .. residential area. residential area. commuting. commuting. In most English-speaking regions , suburban areas are defined in contrast to central or inner city areas , but in Australian English and South African English , `` suburb '' has become largely synonymous with what is called a `` neighborhood '' in other countries and the term extends to inner city areas .. English-speaking regions. English-speaking world. central. Central business district. inner city. inner city. Australian English. Australian English. South African English. South African English. neighborhood. neighborhood. In some areas , such as Australia , China , New Zealand , the United Kingdom , and a few U.S. states , new suburbs are routinely annexed by adjacent cities .. Australia. Australia. China. China. New Zealand. New Zealand. United Kingdom. United Kingdom. annexed. annexed. In others , such as Arabia , Canada , France , and much of the United States , many suburbs remain separate municipalities or are governed as part of a larger local government area such as a county .. Arabia. Arabia. Canada. Canada. France. France. United States. United States. municipalities. Municipality. local government. local government. county. county. Suburbs first emerged on a large scale in the 19th and 20th centuries as a result of improved rail and road transport , which led to an increase in commuting .. commuting. commuting. In general , they have lower population densities than inner city neighborhoods within a metropolitan area , and most residents commute to central cities or other business districts ; however , there are many exceptions , including industrial suburbs , planned communities , and satellite cities .. central. Central business district. inner city. inner city. population densities. population density. commute. commuting. business districts. business districts. planned communities. planned communities. satellite cities. satellite cities. Suburbs tend to proliferate around cities that have an abundance of adjacent flat land .