Appearance of cytochrome oxidase stained cortical tissue across development.

<p>Photomicrographs of cortex that has been flattened, sectioned tangentially and then stained for CO in P5 (top) through adult (bottom) subjects. Portions of the primary sensory areas, especially somatosensory cortex, are visible in all sections, but individual sections do not show all of the boundaries of a field. Images were imported into Adobe Photoshop and levels were adjusted to increase contrast. In all photomicrographs, medial is to the top and rostral is to the left.</p

Functional S1 maps in P5 and P10 rats.

<p>Reconstructed functional maps of primary somatosensory cortex in P5 (A and B) and P10 (C and D) rats. A schematic of a rat body is divided into different major sections: the head, portions of the face and the vibrissae are red, the trunk and tail are blue, the forelimbs are yellow, and the hindlimbs are green. Recording sites that contained neurons that had receptive fields on these major parts are shown as circles filled with that color (i.e., yellow). Recording sites that contained neurons that responded to multiple body parts are labeled with the colors of all of the corresponding body parts. Recording sites that did not respond to any somatosensory stimulation are marked with an X. At P5, medial portions of S1 that normally represent portions of the limbs and trunk contain representations of the face/vibrissae with only a few sites containing neurons responsive to stimulation of the contralateral body. By P10, representations of body parts are beginning to emerge. Conventions as in previous figures.</p

Receptive field progressions in an adult rat.

<p>Progressions of recording sites in S1 in an adult rat (left in A) and corresponding receptive fields for neurons at those sites (right in A). Numbered sites in the cortex correspond to numbered receptive fields on the body. Receptive fields are shaded grey. In adults, the topographic organization is precise and consistent across animals. As recording sites progress from medial to lateral in the caudal portion of S1 (sites 1–4) corresponding receptive fields move from the tail, lower trunk to upper trunk. The hindpaw (5–7) and forepaw (8–10) have corresponding progression from toes 5–1 and digits 5–1, respectively. Compare this figure with the full map of the body illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032322#pone-0032322-g001" target="_blank">Figure 1</a>. B) Representative trace of cortical activity in response to stimulation of digits of the contralateral digit 4 (top left) in an adult rat. In the top left drawing of the forepaw, each digit is labeled with its corresponding number, and the receptive field on dorsal digit 4 is shaded in grey. In the bottom left is a schematic of S1 with the recording site marked with an open circle (scale = 1 mm). A trace of multi-unit activity is located to the right of the forepaw schematic. Tic marks represent the temporal pattern of stimulation. Peri-event histograms, labeled with their corresponding digit, show the increase in the amount of cortical activity in the 1 second surrounding digit stimulation.</p

Functional S1 maps in P15 and P20 rats.

<p>Reconstructed functional maps of primary somatosensory cortex in P15 (A and B) and P20 (C and D) rats. At P15, normal somatotopy is beginning to emerge, but there is still considerable variability in map organization between individuals (compare A and B). By P20, the functional maps have an adult-like organization. Conventions as in previous figures.</p

Brain Weights in grams.

<p>Brain Weights in grams.</p

Laterality of Receptive Fields.

<p>Laterality of Receptive Fields.</p

Receptive field progressions in P20 and P15 rats.

<p>A) Progressions of recording sites in S1 in a P20 rat (left) and corresponding receptive fields for neurons at those sites (right). In P20 rats, the topographic organization is similar to that seen in adults. As recording sites progress from medial to lateral in the caudal portion of S1 (sites 1–3) corresponding receptive fields move from the tail, hindlimb and lower trunk to upper trunk and face. Compared to adults, receptive fields on the hindpaw (4–6) and forepaw (8–10) are larger and can encompass multiple digits, toes, or pads. B) Progressions of recording sites in S1 in a P15 rat (left) and corresponding receptive fields for neurons at those sites (right). In P15 rats the topographic representation is less well-organized and there is greater variability between animals. Receptive fields are larger and can encompass more than one body part (i.e., site 7). As recording sites progress from medial to lateral in the caudal portion of S1 (1–3) corresponding receptive fields move from the tail and lower trunk, to the middle trunk and head. Most often receptive fields are on the entire foot (4–5) or large portions of the forepaw (7–10). Compare this figure with the full map of the body illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032322#pone-0032322-g001" target="_blank">Figure 1 </a><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032322#pone.0032322-Karlen1" target="_blank">[102]</a>. Conventions as in previous figures.</p

Brain Areas in mm².

<p>Brain Areas in mm².</p

Changes in brain and body size across development.

<p>A) Scaled pictures of Long Evans rats at P5, P10, P15, P20, and during adulthood. B) The relative sizes of the rat brains at the same ages. While both the size and shape of the body change dramatically across development, the size and shape of the brain changes less significantly than the body.</p

Changes in brain weight across development.

<p>A) Changes in the weight (in grams) of the whole brain, left hemisphere, right hemisphere, and subcortical regions across development. B) Changes in the weight of the left hemisphere, right hemisphere, and subcortical regions as a percentage of the weight of the whole brain across development. * - significantly different from all other ages. † - significantly different from P5, P10, and adult. Mean + s.d.</p