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Cerebral Cortex Advance Access originally published online on March 16, 2005
Cerebral Cortex 2005 15(11):1791-1803; doi:10.1093/cercor/bhi056
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org

Disruption of Layer 4 Development Alters Laminar Processing in Ferret Somatosensory Cortex

Debra F. McLaughlin and Sharon L. Juliano

Department of Anatomy and Cell Biology, and Program in Neuroscience, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA

Address correspondence to Debra F. McLaughlin or Sharon L. Juliano, Department of Anatomy and Cell Biology, USUHS, 4301 Jones Bridge Road, Bethesda, MD 20814, USA. Email: dmclaughlin{at}usuhs.mil or sjuliano{at}usuhs.mil

Treatment with the anti-mitotic agent methylazoxymethanol (MAM) on embryonic day 33 (E33) in ferrets changes features of somatosensory cortex. These include dramatic reduction of cells in layer 4, and altered distributions of thalamocortical afferent terminations and GABAA receptors. To determine the effect of the relative absence of layer 4 on processing of sensory stimuli we used current source-density profiles to assess laminar activity patterns. Nearly synchronous activation occurs across all layers in treated animals, which contrasts with the normal cortical activation pattern of initial sinks in layer 4. This change after MAM treatment is consistent with the absence of layer 4 cells and widespread termination of thalamocortical afferents. Using periodic stimulation at ‘flutter’ frequency, layer 4 neurons in normal somatosensory cortex fire reproducibly to the stimulus rate; the capacity for entrainment is best for layer 4 and weaker in the extragranular layers. The capacity to encode periodic sensory stimuli is disrupted in MAM-treated somatosensory cortex; after an initial response to the onset of periodic stimuli, neurons in all cortical layers show weak entrainment. Neural responses to sensory drive in E33 MAM-treated cortex are also embedded in levels of neural activity substantially above those in normal somatosensory cortex. Sustained stimulation additionally reveals different capacities in each layer for improved signal-to-noise ratios, with layer 4 neurons in normal animals exhibiting the most improved signaling over time. We conclude that normal thalamic terminations, an intact layer 4 and subsequent intracortical processing are integral to proper encoding of stimulus features.

Key Words: cortical dysplasia • cortical information processing • current source-density • multiple unit activity • MAM • neocortical layers


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S. Poluch, B. Jablonska, and S. L. Juliano
Alteration of Interneuron Migration in a Ferret Model of Cortical Dysplasia
Cereb Cortex, January 1, 2008; 18(1): 78 - 92.
[Abstract] [Full Text] [PDF]


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