Figure legends
Fig. 1 : (A) Lateral view of the ferret cerebral cortex
displaying the rostral posterior parietal cortex (PPr). The box shows
the enlarged PPr area below, with the large dots representing the
location of recording penetrations (not all displayed due to overlap).
(B) The experiment involved multiple single-unit recordings of responses
evoked by the presentation of a visual (white bar moved
nasal-to-temporal across a screen), a tactile stimulus (1 g calibrated
fiber moved across skin/hairs by an electronically controlled actuator),
or the combination of both visual and tactile stimulation. (C) Examples
of single-unit neuronal responses recorded after visual alone, tactile
alone and combined visual- tactile stimulation. Top row shows the
responses of a unimodal visual neuron (left) and a unimodal tactile
neuron (right). The middle row depicts a bimodal PPr neuron that
generated multisensory enhancement (left) (combined response
significantly greater than most effective unimodal response) and another
bimodal neuron (right) that generated multisensory response depression.
Bottom row shows a subthreshold multisensory response where a combined
stimulus significantly enhances (left) or depresses (right) activity
with a stimulus from a different modality that is not effective when
presented alone.
Fig. 2. Sensory and multisensory neurons in PPr show
proportional changes from infancy and across adolescence. (A) The
histograms indicate the average (± SE) proportion of a particular neuron
response type (V=unimodal visual; T=unimodal tactile; S=Subthreshold
multisensory; B=bimodal multisensory) during the different developmental
epochs (yellow=infancy; blue=early adolescence; green=middle
adolescence; red=late adolescence; see Methods for definitions). (B) The
same data as in part ‘A’ except now plotted with lines connecting the
different response types across development.
Fig. 3 : Responsiveness (average number of spikes/response ± SE)
of PPr neuron types (Unimodal =unisensory visual and unisensory tactile;
Bimodal multisensory; Subthreshold multisensory) across developmental
stages (Infancy=yellow; early adolescence=blue; middle
adolescence=green; late adolescence- red). For subthreshold neurons,
only one subthreshold such neuron was identified in infancy. Univariate
ANOVA followed by posthoc Bonferroni tests * = p<0.05; ** =
p<0.01.
Fig. 4 : Spontaneous activity (spikes/sec ± SE; recorded 500 ms
before sensory stimulation) in unimodal (unisensory visual and
unisensory tactile), bimodal multisensory and subthreshold multisensory
neurons across the developmental periods (Infancy=yellow; early
adolescence=blue; middle adolescence=green; late adolescence=red). For
the subthreshold category, only one neuron was identified in infancy.
Univariate ANOVA followed by posthoc Bonferroni tests* =
p<0.05; ** = p<0.01.
Fig. 5: A. Responses of PPr neurons to multisensory stimulation
across the developmental stages. (A) Pie charts indicate the
p roportions of bimodal neurons that exhibited significant multisensory
integration in the different age groups. B . For bimodal neurons
that demonstrate MSI, these box/whisker plots show the significant
increase in the magnitude of MS enhancement. No enhancement was seen
during Infancy; the Early adolescence group was significantly different
from Mid and Late adolescence ones. KW followed by Post Hoc Mann Whitney
tests, p<0.01 in both comparisons. Mid and Late adolescence
groups were not different from each other. C. For bimodal
neurons that failed to demonstrate significant MSI, these box/whisker
plots show the significant increase in response levels across the
developmental stages. KW followed by Post Hoc Mann Whitney tests, * =
p<0.05. D. Cumulative probability plots of response
changes after combined VT stimulation in all bimodal neurons
(integrative and non-integrative) across four age groups. A
Kruskall-Wallis non-parametric ANOVA (KW) followed by post-hoc
Kolmogorov-Smirnov tests showed that all groups were significantly
different from each other (p<0.05 for all comparisons). These
data show that both integrative and non-integrative bimodal responses
exhibit developmental changes that shift from primarily suppressive
responses in neurons from infants to progressively higher response
changes in adolescents.
Fig. 6: (A) For all subthreshold multisensory neurons, although
present in each age group, their multisensory responses (box/whisker
plots for each age group) do not show significant changes in magnitude
across the different developmental stages. KW non-parametric ANOVA. Not
significant. Only a single subthreshold neuron was observed during
infancy (yellow circle). B. For subthreshold multisensory
neurons that exhibited response enhancement, the bar graphs (± SE) show
that the average magnitude of multisensory enhancement was not affected
by developmental age. (Univariate ANOVA. Not significant). C.For subthreshold multisensory neurons that exhibited response
depression, the bar graphs (± SE) show that the average magnitude of
multisensory depression also was not affected by developmental age
(Univariate ANOVA; Not significant).
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