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E M Rouiller

Publications and source records attributed to E M Rouiller.

At least 19 recordsLinked to original sources
PubMed1999

Origin of thalamic inputs to the primary, premotor, and supplementary motor cortical areas and to area 46 in macaque monkeys: a multiple retrograde tracing study.

The origin of thalamic inputs to distinct motor cortical areas was established in five monkeys to determine whether the motor areas receive inputs from a common thalamic nucleus and the extent to which the territories of origin overlap. To not rely on the rough definition of cytoarchitectonic boundaries in the thalamus, monkeys were subjected to multiple injections of tracers (four to seven) in the primary (M1), premotor (PM), and supplementary (SMA) motor cortical areas and in area 46. The cortical areas were distributed into five groups, each receiving inputs from a specific set of thalamic nuclei: 1) M1; 2) SMA-proper and the caudal part of the dorsal PM (PMdc); 3) the rostral and caudal parts of the ventral PM (PMvr and PMvc); 4) the rostral part of the dorsal PM (PMdr); and 5) the superior and inferior parts of area 46 (area 46sup and area 46inf). A major degree of overlap was obtained for the origins of the thalamocortical projections directed to areas 46inf and 46sup and for those terminating in SMA-proper and PMdc. PMvc and PMvr received inputs from adjacent and/or common thalamic regions. In contrast, the degree of overlap between M1 and SMA was smaller. The projection to M1 shared relatively limited zones of origin with the projections directed to PM. Thalamic inputs to the motor cortical areas (M1, SMA, PMd, and PMv), in general, were segregated from those directed to area 46, except in the mediodorsal nucleus, in which there was clear overlap of the territories sending projections to area 46, SMA-proper, and PMdc.

Afferent Pathways↗
PubMed1999

Preferential induction of fos-like immunoreactivity in granule cells of the cochlear nucleus by acoustic stimulation in behaving rats.

Neuronal activity in the cochlear nucleus was mapped in relation to acoustic stimuli that signalled a sensory-motor response, using Fos-like immunoreactivity. Rats were trained to associate an acoustic stimulus with a reward and then to discriminate between two sounds ('learning' rats; n = 18). The same stimuli carrying no behavioural significance were pseudo-randomly presented to 'control' rats (n = 4) to differentiate stimulus related- from learning related-activity. To establish a baseline, Fos-like immunoreactivity was determined in rats (n = 2) unexposed to acoustic stimulation. The number of Fos-positive cells was significantly increased in the rats exposed to sounds ('learning' and 'control') as compared to the non-stimulated animals. This stimulus related increase of Fos-like activity in the cochlear nucleus was most prominent in a subpopulation of small neurons, whose spatial distribution corresponds to that of the granule cells. There was also an increase in the number of Fos-positive neurons of larger size, but less prominent than for the small cells. Brief exposure to sounds (30 s) was sufficient to induce Fos-like activity.

Acoustic Stimulation↗
PubMed1999

Neural activity of supplementary and primary motor areas in monkeys and its relation to bimanual and unimanual movement sequences.

A chronic single-unit study of motor cortical activity was undertaken in two monkeys trained to perform a bimanually coordinated task. The hypothesis was tested that the supplementary motor area plays a specific role in coordinating the two hands for common goal-oriented actions. With this objective, a special search was made for neurons that might exhibit properties exclusively related to bimanual task performance. Monkeys learned to reach for and to pull open a spring-loaded drawer with one hand, while the other hand reached out to grasp food from the drawer recess. The two hands were precisely coordinated for achievement of this goal. Monkeys also performed, in separate blocks of trials, only the pulling or grasping movements, using the same hands as in the bimanual task. Task-related activity of 348 neurons from the supplementary motor area and 341 neurons from the primary motor area, each examined in the bimanual and in both unimanual tasks, was recorded in the two hemispheres. Most neurons from the supplementary motor area were recorded within its caudal microexcitable portion. Contrary to expectation, the proportion of neurons with activity patterns related exclusively to the bimanual task was small, but somewhat higher in the supplementary motor area (5%) than in the primary motor cortex (2%). Another group of neurons that were equally modulated during the bimanual as well as to both unimanual task components might also contribute in controlling bimanual actions. Such "task-dependent" rather than "effector-dependent" activity patterns were more common in neurons of the supplementary motor area (19%) than of the primary motor cortex (5%). Bilateral receptive fields were also more numerous among the supplementary motor area neurons. However, a large majority of neurons from primary and supplementary motor areas had activity profiles clearly related only to contralateral hand movements (65% in the primary motor and 51% in the supplementary motor area). A similar group of neurons showed an additional slight modulation with ipsilateral movements; they were equally common in the two areas (14% and 16%, respectively) and their significance for bimanual coordination is questionable. Summed activity profiles of all neurons recorded in the primary and supplementary motor areas of the same hemisphere were compared. The modulations of the three histograms, corresponding to the two unimanual and the bimanual tasks, were similar for the two motor areas, i.e. prominent with bimanual and contralateral movements and weak with ipsilateral movements. It is concluded that the supplementary motor area is likely to contribute to bimanual coordination, perhaps more than the primary motor cortex, but that it is not a defining function for the former cortical area. Instead, it is suggested that the supplementary motor area is part of a callosally interconnected and distributed network of frontal and parietal cortical areas that together orchestrate bimanual coordination.

Animals↗
PubMed1998

Dual morphology and topography of the corticothalamic terminals originating from the primary, supplementary motor, and dorsal premotor cortical areas in macaque monkeys.

In the motor, somatosensory, and auditory systems of rodents and cats, the corticothalamic connection is composed of a main projection formed by small endings and a minor projection terminating with giant endings. To establish whether the corticothalamic projection originating from motor cortical areas in primates exhibits the same duality, the anterograde tracer biotinylated dextran amine was injected in eight macaque monkeys in the primary motor (M1; n = 3), the supplementary motor (SMA; n = 3) and the dorsal premotor (PMd; n = 2) cortical areas to label corticothalamic axons. The corticothalamic projection originating from these three motor cortical areas was characterized by the presence of axon terminals constituting the same two types of endings, observed both as boutons en passant and terminaux. The population of small endings exhibited a mean cross-sectional maximum diameter of 0.95 microm (S.D. = 0.23), a range of diameters not overlapping that of giant endings (mean diameter = 3.46 microm, S.D. = 0.74 microm). Topographically, the giant endings originating from M1 were located in the same thalamic nucleus (ventroposterolateral nucleus, oral part) in which the small endings were found. In contrast, the giant endings originating from SMA and PMd were located in a thalamic nucleus (mediodorsal nucleus) distinct from the main termination zone formed by small endings. Along the rostrocaudal axis, the giant endings were distributed in a restricted zone, irrespective of the origin of the projection (M1, SMA, PMd). The dual morphology of corticothalamic endings, previously found in rodents and cats, is present in the motor system of subhuman primates for both primary and nonprimary motor cortical areas.

Animals↗
PubMed1998

Effects of lesions in the mesial frontal cortex on bimanual co-ordination in monkeys.

The hypothesis was tested that the mesial frontal cortex, including the supplementary motor area, is engaged in bimanual co-ordination. Three monkeys, trained in a well-co-ordinated bimanual pull-and-grasp task, were subjected to unilateral or bilateral lesions of the mesial frontal cortex. With unilateral lesions, the deficit consisted in a delay in movement initiation of the contralateral arm. With a bilateral lesion, the deficit was more pronounced with marked bilateral delays in movement onset and slowing in reaching. However, in the three monkeys bimanual co-ordination at the moment of goal achievement remained intact with an excellent temporal co-variation of the two limbs. In the two unilateral cases, an adaptive strategy developed after a few sessions, either by catching up during reaching with the limb contralateral to the lesion (monkey M1) or by delaying movement initiation of the limb ipsilateral to the lesion (monkey M2). This outcome is discussed in terms of Lashley's principle of motor equivalence, i.e. invariant goal achievement with variable means. Bilateral lesions led to a transient and near-total impairment in movement self-initiation when all external cues were absent. It is concluded that in monkeys the mesial frontal cortex does not play a crucial role in bimanual co-ordination but rather in movement initiation, especially when sensory cues are absent.

Animals↗
PubMed1998

Discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus of the rat.

The aim of the present study was to characterize the discharge properties of single neurons in the dorsal nucleus of the lateral lemniscus (DNLL) of the rat. In the absence of acoustic stimulation, two types of spontaneous discharge patterns were observed: units tended to fire in a bursting or in a nonbursting mode. The distribution of units in the DNLL based on spontaneous firing rate followed a rostrocaudal gradient: units with high spontaneous rates were most commonly located in the rostral part of the DNLL, whereas in the caudal part units had lower spontaneous discharge rates. The most common response pattern of DNLL units to 200 ms binaural noise bursts contained a prominent onset response followed by a lower but steady-state response and an inhibitory response in the early-off period. Thresholds of response to noise bursts were on average higher for DNLL units than for units recorded in the inferior colliculus under the same experimental conditions. The DNLL units were arranged according to a mediolateral sensitivity gradient with the lowest threshold units in the most lateral part of the nucleus. In the rat, as in other mammals, the most common DNLL binaural input type was an excitatory response to contralateral ear stimulation and inhibitory response to ipsilateral ear stimulation (EI type). Pure tone bursts were in general a more effective stimulus compared to noise bursts. Best frequency (BF) was established for 97 DNLL units and plotted according to their spatial location. The DNLL exhibits a loose tonotopic organization, where there is a concentric pattern with high BF units located in the most dorsal and ventral parts of the DNLL and lower BF units in the middle part of the nucleus.

Acoustic Stimulation↗
PubMed1998

Dexterity in adult monkeys following early lesion of the motor cortical hand area: the role of cortex adjacent to the lesion.

Infant monkeys were subjected to unilateral lesions of the motor cortex (mainly its hand representation). After maturation, they showed normal use of the contralateral hand for global grip movements. However, as compared with the ipsilateral hand, precision grip tasks requiring relatively independent finger movements were performed with less dexterity, particularly if adjustments of the wrist position were necessary. The purpose of this study was to investigate mechanisms which may be responsible for the rather well, although not complete, preservation of manipulative behaviour of these adult monkeys. To this end, the hand representations were mapped bilaterally with intracortical microstimulation in the mature monkeys, and the dexterity of both hands assessed quantitatively in a precision grip task. The behavioural effects of reversible inactivations of the primary (M1) and supplementary (SMA) motor cortical areas were then tested. The following were found. (i) The hand contralateral to the lesion exhibited subtle but significant dexterity deficits, as compared with the ipsilateral hand; the deficit was essentially for complex movements requiring dissociation of the thumb-index finger pinch from the other digits, involving also an arm rotation. (ii) Reversible inactivation of the M1 hand representation in the intact hemisphere dramatically impaired dexterity of the opposite hand without affecting the ipsilateral hand (contralateral to the early lesion). (iii) A relatively complete hand representation was found to occupy a new territory, medial to the old lesion. (iv) The role of this new displaced representation was crucial for the preserved dexterity of the opposite hand, as evidenced by its functional inactivation. In contrast, inactivation of both SMA cortices did not interfere with the manipulative behaviour. It is thus concluded that the preserved functional capacity of manipulations with the hand opposite the early lesion can be essentially attributed to a cortical reorganization around the old lesion. Under the present experimental conditions, contributions from either the SMA or the intact M1 appear not to be crucial.

Animals↗
PubMed1998

Neuronal activity in the primate supplementary motor area and the primary motor cortex in relation to spatio-temporal bimanual coordination.

Single neuronal activity was recorded from the supplementary motor area (SMA-proper and pre-SMA) and primary motor cortex (M1) in two Macaca fascicularis trained to perform a delayed conditional sequence of coordinated bimanual pull and grasp movements. The behavioural paradigm was designed to distinguish neuronal activity associated with bimanual coordination from that related to a comparable motor sequence but executed unimanually (left or right arm only). The bimanual and unimanual trials were instructed in a random order by a visual cue. Following the cue, there was a waiting period until presentation of a "go-signal", signalling the monkey to perform the instructed movement. A total of 143 task-related neurons were recorded from the SMA (SMA-proper, 62; pre-SMA, 81). Most SMA units (87%) were active in both unimanual contralateral and unimanual ipsilateral trials (bilateral neurons), whereas 9% of units were active only in unimanual contralateral trials and 3% were active only in unimanual ipsilateral trials. Forty-eight per cent of SMA task-related units were classified as bimanual, defined as neurons in which the activity observed in bimanual trials could not be predicted from that associated with unimanual trials when comparing the same events related to the same arm. For direct comparison, 527 neurons were recorded from M1 in the same monkeys performing the same tasks. The comparison showed that M1 contains significantly less bilateral neurons (75%) than the SMA, whereas the reverse was observed for contralateral neurons (22% in M1). The proportion of M1 bimanual cells (53%) was not statistically different from that observed in the SMA. The results suggest that both the SMA and M1 may contribute to the control of sequential bimanual coordinated movements. Interlimb coordination may then take place in a distributed network including at least the SMA and M1, but the contribution of other cortical and subcortical areas such as cingulate motor cortex and basal ganglia remains to be investigated.

Animals↗
PubMed1998

Antibody-dependent Fos-like immunoreactivity (FLI) in the auditory pathway of the rat in response to electric stimulation of the cochlea.

The distribution of Fos-like immunoreactivity (FLI) in the auditory pathway was analyzed and quantified in two groups of rats subjected to a similar electric stimulation of the cochlea, but the brains of the two groups were treated with a different antibody against Fos. The brains of control (unstimulated) rats were processed and analyzed in the same way. In a given auditory nucleus, for the same paradigm of stimulation, a very different density of FLI can be found depending on the antibody used to process the tissue. There are auditory nuclei which exhibited a significant activation of FLI as compared to control animals when one antibody was used whereas there was no difference when using the other antibody. In other cases, for both antibodies, a significant FLI increase was observed in relation to the stimulus. However, the increase of FLI density was significantly greater in some auditory nuclei with one antibody, while it was the reverse in other auditory nuclei. The present data demonstrate quantitatively that the use of two different Fos antibodies can strongly affect the FLI produced in the auditory pathway by electric stimulation of the cochlea, confirming previous qualitative observations based on acoustic stimulation of the cochlea.

Animals↗
PubMed1997

Effects of reversible inactivation of the supplementary motor area (SMA) on unimanual grasp and bimanual pull and grasp performance in monkeys.

The supplementary motor area (SMA) was reversibly inactivated by muscimol microinfusion in two monkeys while they were performing two motor tasks: (1) a delayed conditional bimanual drawer pulling and grasping sequence which was initiated on a self-paced basis; (2) a unimanual reach and grasp task (modified Kluver board task). Unilateral or bilateral inactivation of the SMA induced a prominent deficit in trial initiation of bimanual sequential movements, affecting the hand contralateral to the inactivated side or both hands, respectively. The deficit was a long lasting (10-15 min or more) inability of the monkey to place its hand (s) in the ready position on start touch-sensitive pads, a condition required to initiate the drawer task. However, if after such a deficit period, the experimenter put his hand on the start touch-sensitive pad to initiate the trial, then the monkey executed the drawer task without obvious motor deficit. SMA inactivation did not affect unimanual reaching and grasping movements in the board task. In contrast to the SMA, inactivation of other motor areas (primary, premotor dorsal, anterior intraparietal area) did not affect the initiation of movement sequences in the drawer task. These data thus indicate that the SMA plays a crucial and specific role in initiation of self-paced movement sequences. However, SMA inactivation did not prevent the monkeys to perform coordinated movements of the two forelimbs and hands, indicating that SMA is not necessary for bimanual coordination.

Animals↗
PubMed1997

Effect of high-frequency electrical stimulation of the auditory nerve in an animal model of cochlear implants.

HYPOTHESIS: Electrical stimulation of the cochlea at high rates induces significant adaptation of the auditory nerve. BACKGROUND: A new development of cochlear implants is the use of speech processors delivering electrical pulses on the implanted electrodes at high rates, such as 1,000 pulses per second (pps) and above. Such a stimulation mode allows subjects with cochlear implants to reach excellent understanding of speech. METHODS: Long Evans-rats received implantation of stimulating electrodes in the left cochlea. Two hundred-millisecond trains of short (20 microns) monophasic pulses were delivered in 50% duty cycle at 500 microA above threshold. The pulse rate in the train was increased from 100 pps to 1,500 pps. Electrically evoked auditory brainstem responses (EABR) were recorded. The amplitude of the compound action potential of the auditory nerve to each single pulse in the train was measured as the first vertex positive wave (WAVE I) of the EABR. RESULTS: At 100 and 200 pps, WAVE I amplitudes to each pulse were large and remained stable throughout the pulse train. For increasing pulse rates, WAVE I amplitudes progressively decreased during the first 40 to 50 ms of the train and reached 80% at 300 pps to 15% at 1,500 pps of the maximal amplitude observed for the first pulse in the train. CONCLUSIONS: The decrease of the WAVE I amplitude in response to high-rate pulsatile stimulation reflects an adaptation of the auditory nerve due, at least in part, to the refractory period of auditory nerve fibers.

Acoustic Stimulation↗
PubMed1996

Electrically induced fos-like immunoreactivity in the auditory pathway of the rat: effects of survival time, duration, and intensity of stimulation.

The goal of the present study was to establish how Fos-like immunoreactivity (FLI) elicited in the rat auditory pathway by unilateral electric stimulation of the cochlea is affected by the following experimental parameters: duration and intensity of stimulation, duration of survival time after offset of stimulation. The dense FLI found in the ipsilateral dorsal cochlear nucleus, as well as the moderate FLI found in the contralateral dorsal cochlear nucleus and in the posteroventral cochlear nucleus on both sides, were consistent after survival times ranging from 0 to 2-3 h, but they significantly decreased after longer survival times (5 and 6 h). In the same nuclei, FLI was increased even by short durations of stimulation (5 and 10 min) as compared to control rats, although FLI progressively increased for longer stimulation (20 and 45 min). In the auditory thalamus, FLI was found mainly in the peripeduncular nucleus, the dorsal and medial divisions of the medial geniculate body, whereas its ventral division was virtually devoid of immunoreactive neurons. This pattern of FLI distribution in the auditory thalamus persisted even after relatively long survival times (5 and 6 h). In both the cochlear nucleus and auditory thalamus, the density of FLI slightly increased in parallel with the intensity of stimulation. In other auditory nuclei, such as the inferior colliculus and the nucleus of the lateral lemniscus, there was no simple relation between the density of FLI and the three tested experimental parameters. Thus, the distribution and density of FLI did not vary in parallel in the various nuclei of the auditory pathway as a function of the tested experimental parameters; different patterns of FLI changes were instead observed in different auditory nuclei.

Action Potentials↗
PubMed1996

Evidence for direct connections between the hand region of the supplementary motor area and cervical motoneurons in the macaque monkey.

In primates the corticospinal neurons of the hand representation of the primary motor cortex (M1) give rise to direct contacts with the cervical motoneurons that control distal forelimb muscles. We investigated, at the light-microscopy level, whether corticospinal cells present in the hand area of the supplementary motor area (SMA) also establish direct connections with cervical motoneurons, particularly those innervating hand and finger muscles. The hand representation of the M1 (two monkeys) or SMA (two monkeys) was located using intracortical microstimulation and injected with the anterograde tracer biotinylated dextran amine to label corticospinal terminals. Forearm muscles acting on the wrist and hand as well as hand muscles acting on the thumb and index finger, thus including those activated by intracortical stimulation, were injected with the retrograde tracer cholera-toxin B subunit, in order to label the motoneurons. A consistent zone of overlap between the two markers was found in the cervical cord. Close appositions between corticospinal axonal terminals and the somata or dendrites of motoneurons were found after injection in the M1, confirming previous observations. The new finding is the observation of similar close appositions after injection in the SMA, suggesting its control of hand movements in parallel with the M1.

Animals↗
PubMed1995

Direct visual pathways for reaching movements in the macaque monkey.

The brain seems to process the location of objects faster than their intrinsic features, such as size, when these parameters are used to guide action. To uncover a potential anatomical substrate of these different processing speeds, we investigated in the monkey the pathways linking extrastriate visual cortex with the dorsal premotor area, a frontal area known to be involved in visually guided reaching movements. Retrogradely transported anatomical tracers were injected at physiologically defined sites and the distribution of labelled cells was examined in the ipsilateral cortex. We found a projection to the dorsal premotor cortex from the parieto-occipital area (PO). This area receives direct projections from the primary visual cortex (V1), and is part of the dorsal visual stream involved in the processing of spatial information. No direct projections to the dorsal premotor cortex arise from the ventral visual areas, thought to process object features. Our finding provides evidence for direct pathways from the dorsal visual stream to the dorsal premotor cortex and supports the view that the location of objects is processed faster by the brain than their intrinsic features.

Animals↗
PubMed1995

The auditory pathway in cat corpus callosum.

The cortical auditory fields of the two hemispheres are interconnected via the corpus callosum. We have investigated the topographical arrangement of auditory callosal axons in the cat. Following circumscribed biocytin injections in the primary (AI), secondary (AII), anterior (AAF) and posterior (PAF) auditory fields, labelled axons have been found in the posterior two-thirds of the corpus callosum. Callosal axons labelled by small individual cortical injections did not form a tight bundle at the callosal midsagittal plane but spread over as much as one-third of the corpus callosum. Axons originating from different auditory fields were roughly topographically ordered, reflecting to some extent the rostro-caudal position of the field of origin. Axons from AAF crossed on average more rostrally than axons from AI; the latter crossed more rostrally than axons from PAF and AII. Callosal axons originating in a discrete part of the cortex travelled first in a relatively tight bundle to the telo-diencephalic junction and then dispersed progressively. In conclusion, the cat corpus callosum does not contain a sector reserved for auditory axons, nor a strictly topographically ordered auditory pathway. This observation is of relevance to neuropsychological and neuropathological observations in man.

Animals↗
PubMed1995

Morphology and spatial distribution of corticothalamic terminals originating from the cat auditory cortex.

In this paper we studied the morphology and spatial distribution of corticothalamic axons and terminals originating from the auditory cortical fields of the cat. The anterograde tracer biocytin was injected at electrophysiologically characterized loci in the primary (AI) (N = 2), anterior (AAF) (N = 1), posterior (PAF) (N = 1) and secondary (AII) (N = 2) auditory fields. In all cases, two different types of labeled terminals were found in the auditory thalamus: small spherical endings (1-2 microns) and giant, finger-like endings (5-10 microns). After biocytin injections in AI and AAF, the majority of anterogradely labeled axons terminated in the rostral half of the pars lateralis (LV) of the ventral division of the medial geniculate body (vMGB). In LV, the corticothalamic axons ramified profusely, giving rise to dense terminal fields forming well delineated curved stripes, with small spherical endings. Additional terminal fields formed by small endings were observed in the medial division of the medial geniculate body (mMGB). Giant endings were observed in a small area in the dorsal nucleus (D) of the dorsal division of the medial geniculate body (dMGB), near its border with the vMGB. PAF projections were located in the caudal half of vMGB and in mMGB, where only small terminals were found. Giant endings were seen in the superficial part of dMGB emerging from labeled corticothalamic axons oriented in parallel to the dorsal surface of the MGB. Projections from AII gave rise to a main terminal field of small endings in D; a second terminal field consisting of giant endings intermingled with small endings was found in the deep dorsal nucleus (DD) of dMGB. We conclude that small terminals serve the feedback projection to the thalamic nucleus from which the injected cortical field receives its main input, whereas giant terminals cross the borders between the parallel ascending auditory pathways.

Acoustic Stimulation↗
PubMed1995

Re-examination of the plasticity of the corticothalamic projection after unilateral neonatal lesion of the sensorimotor cortex in the rat: a phaseolus vulgaris-leucoagglutinin tracing study.

After unilateral lesion of the sensorimotor cortex in neonatal rats (postnatal days 2-4), the reorganization of the corticothalamic projection originating from the opposite intact sensorimotor cortex was studied. Three months after the lesion, the anterograde tracer phaseolus vulgaris-leucoagglutinin (PHA-L) was injected in the caudal forelimb area (CFA) of the intact opposite sensorimotor cortex to label the corticothalamic axons, in order to establish their trajectory as well as the distribution of their terminal fields in the thalamus. As previously reported, in addition to the standard ipsilateral corticothalamic projection, lesioned rats were characterized also by the presence of a contralateral corticothalamic projection, reaching the decorticate hemithalamus. There is some controversy in literature whether such bilateral corticothalamic projection is present in normal intact rats. On the basis of counts of axons crossing the midline to innervate the hemithalamus contralateral to the cortical injection, the present study provides evidence that the corticothalamic projection is indeed bilateral in normal rats, although the contralateral projection is sparse. Lesioned rats subjected to a similar small size PHA-L injection in the CFA of the intact opposite cortex showed a significantly increased contralateral corticothalamic projection. The number of labeled axons crossing the midline in the thalamus was, on average, five times higher in lesioned rats than in normal rats. It can be concluded that the contralateral corticothalamic projection from the CFA, observed after neonatal lesion of the opposite sensorimotor cortex, is not a novel projection resulting from the lesion, but rather an enhancement and extension of an existing, minor, projection present in normal rats. The enhancement of the crossing corticothalamic projection in lesioned rats is due to an increase of the number of crossing axons in the thalamus rather than to an increase of the degree of branching of the few axons present in control animals.

Animals↗