FoundationalConceptsNeuroscience

rons in the premotor areas of the frontal lobes that are active during
particular movements and also active when these movements are
observed in another person. For example, if 1 am moving my arm in
a specific way, collections of neurons in my premotor areas are active
during the organization and execution of this movement. Some of
these neurons may also fire when I see other people move their arms
in a similar way. Such cells have been termed “mirror neurons.” The
implications of this kind of extensive cortical interconnectivity are
the subject of active investigation and theorizing. The concept of
mirror neurons has been invoked, for example, in speculations about
the origins of language (see Chapter 18). It has also been invoked as
a contributor to the neural basis of empathic connection between
individuals—that is, the ability to connect with another person’s emo-
tional experience.
Another part of the brain that is centrally involved in the regulation
of movement is the cerebellum, which wraps around the brainstem
and is very densely packed with neurons and neural connections.
Estimates of the number of nerve cells in the human cerebellum
are upward of fifty billion, meaning there are more neurons in the
cerebellum alone than there are in all the rest of the brain. One
type of cerebellar neuron is the Purkinje cell, named after the Czech
anatomist and physiologist Jan Purkyng (1787-1869), who first de-
scribed these neurons. Each Purkinje cell may have several hundred
thousand dendritic spines receiving input from other neurons (Fig.
16.6).
The cerebellum is involved in the timing and coordination of move-
ment. Individuals who have sustained damage to their cerebellum are
not paralyzed, but they are impaired in their ability to smoothly exe-
cute movements. Even simple movements become jerky and clumsy.
Movements are notably compromised in timing, leading to ideas