136 NOTES TO CHAPTER 1
was willing to live with and consort in private, but with whom he was reluctant
to be seen in public” (cited in Valenstein 2005, 131). Dale was ultimately victori-
ous; chemical transmission is now understood as the primary form of commu-
nication in the nervous system. The current view is that chemical synaptic trans-
mission characterizes the majority of communication in the brain. In 1950 gap
junctions, which seem to allow electrical current to pass directly from one cell to
another, were also identified.
5 Further, differences in intervals between pulses had an impact on how many
synapses were affected. In the 1980s Hebbian plasticity and long- term potenti-
ation helped to build a connectionist model of cognition. Connectionists argue
that cognition comprises the activations of networks of neurons that are distrib-
uted across the brain. Neurons at different locations in the network calculate the
strength of their own activation based on the firing rates of inputs from other
neurons. These calculations also are weighted by past exposure to stimulation,
which affects the neurons’ amplitudes. The knowledge held in neural networks
“is contained in and defined by its very architecture, in the connection weights
that currently hold among all units as a function of prior learning” (Bates and
Elman 2002, 431).
6 In A Thousand Plateaus, Deleuze and Guattari characterize synaptic plasticity
in terms of the agency it affords to neurobiological matter: “What are wrongly
called ‘dendrites’ do not assure the connections of neurons in a continuous fab-
ric. The discontinuity between cells, the role of the axons, the functioning of the
synapses, the existence of synaptic microfissures, the leap each message makes
across these fissures, make the brain a multiplicity immersed in its plane of con-
sistency or neuroglia, a whole uncertain, probabilistic system.. .” (1987, 15). See
Murphie 2010 and Dewsbury 2011 for discussion.
7 Some models argue for considerable experience dependence in the brain’s matu-
ration. In their manifesto of neural constructivism, Steven Quartz and Terrance
Sejnowski (1997) argue that humans begin life with a “protocortex,” which has
basic circuitry but develops regional specializations only through input from
the rest of the body and the environment to the brain. They argue that cortical
wiring is progressively elaborated through the interaction of mechanisms that
are dependent on experience with developmental trajectories that are intrinsic
(Quartz 1999). Although neural constructivists acknowledge genetic processes,
they emphasize epigenetics, or the varying ways genes are expressed as the envi-
ronment affects them.
8 Neuroimaging technologies are used to create visual images of brain structures
and processes. mri scans, for example, create computerized, two- dimensional
images of brain tissue that look similar to X- rays, whereas fMRI scans depict
oxygenation levels in the brain to approximate neural activity in different brain
regions. There are a number of methodological limitations to imaging research
that are addressed in the growing critical literature on neuroscience. Joe Dumit
(2004), for example, has offered an exhaustive account of the fallacy of “picturing