Figure 1.
The topographic organization of the primary somatosensory area in adult rats.
As in all other mammals examined, the contralateral body is represented from hindlimb to forelimb to face in a mediolateral progression. The individual toes of the hindpaw and digits of the forepaw are represented rostrally, the proximal limbs caudal to this and the trunk most caudally. In rats, there is a large magnification of the vibrissae of the face. In this and following figures, the head representation is shaded red, the forelimb representation is yellow, the hindlimb representation is green, and the trunk representation is blue. In this figure, unresponsive zones (UZ) are represented in black. Modified from Chapin and Lin, 1984.
Table 1.
List of Abbreviations.
Figure 2.
Changes in brain and body size across development.
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.
Table 2.
Subject Information.
Figure 3.
Changes in brain weight across development.
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.
Table 3.
Brain Weights in grams.
Figure 4.
Reconstruction of architectonic borders.
A) Photomicrographs are consecutive sections of CO-stained tissue each containing portions of the architectonic boundaries of the primary somatosensory area. Blood vessels appear as small white circles, and the primary sensory areas are visible as more darkly staining areas. The purple stars in all figures represent location of fluorescent probes placed in the brain during electrophysiological recording experiments and marked on the digital photograph of the brain, along with recording sites. By aligning these probes with digital images containing electrophysiological recordings, functional maps of S1 can be accurately matched to cortical architecture. B) The outer boundary of the cortical sheet and blood vessels are drawn along with portions of S1 (red, blue and green lines) that are visible in each section. C) By aligning blood vessels, data from all sections are superimposed onto a single section, and then a single comprehensive reconstruction of architectonic boundaries is drawn (D). In all sections, medial is to the top and rostral is to the left.
Figure 5.
Appearance of cytochrome oxidase stained cortical tissue across development.
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.
Figure 6.
Differential effectiveness of cortical staining techniques.
Photomicrographs of primary somatosensory cortex in 5-HT- (A and B), MBP- (C and D), and myelin-stained sections (E, F, and G) in P5 (A), P10 (B and C), P20 (D and E), and adult (F and G) subjects. Visible barrels are indicated with black arrows, and V1 is indicated with white arrows. Different stains work best at different ages. 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. See Table 1 for abbreviations. Scale bar = 1 mm.
Figure 7.
Measurements of different cortical areas.
The shaded portion of the brain schematic represents the area being measured. A) The mean area (in mm2) of the cortex (including the dorsolateral cortical sheet, pyriform cortex, and olfactory bulb), B) dorsolateral cortical sheet (DLCS), (C) S1, and (D) the percentage of cortex occupied by S1. Note that the size of the complete cortical sheet, DLCS and S1 increases with age. However, the relative size of S1 as measured using architectonic boundaries is unchanged throughout development and adulthood. * - significantly different from adult. † - significantly different from P20. ** - significantly different from P15. Mean + s.d.
Table 4.
Brain Areas in mm2.
Figure 8.
Functional S1 maps in P5 and P10 rats.
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.
Figure 9.
Functional S1 maps in P15 and P20 rats.
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.
Figure 10.
Functional S1 maps in adult rats.
Reconstructed functional maps of primary somatosensory cortex in adult rats (A and B). In adult rats the topographic organization is precise and consistent across animals and similar to that previously described (Chapin and Lin, 1984). Conventions as in previous figures.
Table 5.
Recording Sites.
Table 6.
Laterality of Receptive Fields.
Figure 11.
Receptive field progressions in an adult rat.
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 Figure 1. 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.
Figure 12.
Receptive field progressions in P20 and P15 rats.
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 Figure 1 [102]. Conventions as in previous figures.
Figure 13.
Receptive field progressions in P10 and P5 rats.
A) Progressions of recording sites in S1 in a P10 rat (left) and corresponding receptive fields for neurons at those sites (right). In P10 rats, the topographic organization is imprecise. The receptive fields are very large and many receptive fields cover multiple body parts (i.e., sites 7–9). Vibrissae representations are found throughout S1 in inappropriate locations (i.e., sites 1, 2, 4 and 5). As recording sites progress from medial to lateral in the caudal portion of S1 (1–3) corresponding receptive fields were all on the ipsilateral vibrissae. Recording sites in the far medial location (4, 5), in what would be the hindpaw representation in the adult, had receptive fields on the ipsilateral or vibrissae. Recording sites in medial portions of S1 in what would normally be the forepaw representation (6–9) had receptive fields on the forepaw, split receptive fields on the upper body and vibrissae, bilateral vibrissae and face and vibrissae. B) Progressions of recording sites in S1 in a P5 rat (left) and corresponding receptive fields for neurons at those sites (right). In P5 rats there is no apparent topography. Receptive fields are large, and, when present on the limbs, encompass both hairy and glabrous portions of the paws. Receptive fields are also observed on both the contralateral and ipsilateral body parts. Vibrissae representations are prevalent and found throughout S1. As recording sites progress from medial to lateral in the caudal portion of S1 (1–3) corresponding receptive fields move from the contralateral vibrissae to the lateral trunk. Far medial recording sites (4–5) in what would normally be the hindpaw representation had receptive field on the vibrissae, and in one instance the dorsal and ventral hindpaw. More medial recording sites (6–8), in what would normally be the forepaw representation had receptive fields on the contralateral or bilateral vibrissae, and wrist and vibrissae. Compare this figure with the full map of the body illustrated in Figure 1. Conventions as in previous figures.
Figure 14.
Changes in receptive field size and configuration at different developmental ages.
The top illustration is a schematic of the body map in adults with the hindpaw zone marked in green and the forepaw zone marked in yellow. The receptive fields below for the different postnatal ages are for neurons in recording sites in each of these zones. At P5 there were very few recording sites with neurons that had receptive fields on either the forelimb or hindlimb. For those that did, receptive fields were large, and encompassed the vibrissae as well. With progressively older postnatal ages, the size of receptive fields for neurons in these zones decreased, and in adults, were small and often encompassed only a single digit or toe. Conventions as in previous figures.
Figure 15.
Representative traces of multi-unit activity in a P5 (A) and P15 (B) rat.
A) Multi-unit activity in response to stimulation of both ipsilateral (left) and contralateral (right) vibrissae. Tic marks indicate the temporal pattern of stimulation. The inset box includes a depiction of S1 with the recording site indicated by an open circle (scale = 1 mm). B) Multi-unit activity in response to stimulation of toe 4 (left) and toe 5 (right) of the contralateral hindpaw. The receptive field for the neurons is indicated in gray on the schematic of the contralateral hindpaw. The inset box includes an illustration of S1 with the recording site marked by an open circle (scale = 1 mm).