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A
B
Rearing environment:
Clicks or noise pulses
Neural activity is synchronized
IC
Repetitive
clicks
CN
C
D
Summary of Tuning Curves (Cortex)
Frequency Tuning Curves (IC)
3
100
broader
2
50
Control
1
Control
Noise pulse
Click-reared
0
0
5 10
Stimulus Frequency (kHz)
15
20
25
0 6
Postnatal age (days)
32
64
FIGURE 9.16 The temporal pattern of auditory nerve activity influences the development of frequency
tuning. A. Mice or rats were reared with repetitive broadband stimuli (clicks or noise pulses). B. Stimuli of
this sort activate many hair cells in the cochlear and synchronize the discharge pattern of auditory nerve
fibers. C. Single neurons were recorded in the mouse inferior colliculus (IC), and those from click-reared
animals responded to a broader range of frequencies compared to those from controls. D. Recordings were
also made in the rat auditory cortex, and broader frequency tuning properties were maintained during devel-
opment in noise pulse-reared animals. A larger bandwidth, plotted in octaves, indicates that the neurons were
responding to a greater range of frequencies. (Adapted from Sanes and Constantine-Paton, 1985; Zhang
et al., 2002)
(Snyder et al., 1990). In the experimental situation, the
dendritic endings of the auditory sensory neurons can
be stimulated directly with an electrode that is
implanted within the cochlea. When animals were
reared with repetitive electrical pulses to their cochlea,
a synchronous activity pattern was produced.
Although it was not possible to record frequency
tuning curves because the animals were deafened, a
single position along the cochlea was stimulated elec-
trically while an electrode was lowered through the
inferior colliculus. In normal animals, a single point on
the cochlea evokes a response within a limited region
of tissue, referred to as a spatial tuning curve . In stimu-
lated animals, the spatial tuning curves were much
broader, as if a single position in the cochlea now pro-
jected to a much wider area of the tonotopic map in
the inferior colliculus. Consistent with findings from
the visual pathway, these experiments support the
idea that coactive synapses establish strong connec-
tions during development.
In the visual system, many cortical neurons respond
to stimuli of a specific orientation, or to stimuli that are
moving in a specific direction. Many investigators
have asked whether a specific visual experience can
influence the maturation of complex response proper-
ties, although the activity pattern produced by each
environment is seldom known (Blakemore and
Cooper, 1970; Cynader et al., 1973). When kittens are
reared in a visual environment consisting entirely of
vertical or horizontal stripes, and neurons are later
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