The Journal of Neurophysiology Vol. 86 No. 1 July 2001, pp. 354-367
Copyright ©2001 by the American Physiological Society
Temporal Frequency of Whisker Movement. II. Laminar Organization
of Cortical Representations
Ehud
Ahissar,
Ronen
Sosnik,
Knarik
Bagdasarian, and
Sebastian
Haidarliu
Department of Neurobiology, The Weizmann Institute of Science,
Rehovot 76100, Israel
Ahissar, Ehud,
Ronen Sosnik,
Knarik Bagdasarian, and
Sebastian Haidarliu.
Temporal Frequency of Whisker Movement. II. Laminar Organization
of Cortical Representations. J. Neurophysiol. 86: 354-367, 2001. Part of the information obtained by
rodent whiskers is carried by the frequency of their movement. In the
thalamus of anesthetized rats, the whisker frequency is represented by
two different coding schemes: by amplitude and spike count (i.e.,
response amplitudes and spike counts decrease as a function of
frequency) in the lemniscal thalamus and by latency and spike count
(latencies increase and spike counts decrease as a function of
frequency) in the paralemniscal thalamus (see accompanying paper). Here
we investigated neuronal representations of the whisker frequency in
the primary somatosensory ("barrel") cortex of the anesthetized
rat, which receives its input from both the lemniscal and paralemniscal
thalamic nuclei. Single and multi-units were recorded from layers 2/3,
4 (barrels only), 5a, and 5b during vibrissal stimulation. Typically,
the input frequency was represented by amplitude and spike count in the
barrels of layer 4 and in layer 5b (the "lemniscal layers") and by
latency and spike count in layer 5a (the "paralemniscal layer").
Neurons of layer 2/3 displayed a mixture of the two coding schemes.
When the pulse width of the stimulus was reduced from 50 to 20 ms, the
latency coding in layers 5a and 2/3 was dramatically reduced, while the
spike-count coding was not affected; in contrast, in layers 4 and 5b,
the latencies remained constant, but the spike counts were reduced with
20-ms stimuli. The same effects were found in the paralemniscal and
lemniscal thalamic nuclei, respectively (see accompanying paper). These
results are consistent with the idea that thalamocortical loops of
different pathways, although terminating within the same cortical
columns, perform different computations in parallel. Furthermore, the
mixture of coding schemes in layer 2/3 might reflect an integration of
lemniscal and paralemniscal outputs.
