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This study examined the acquisition of a T-maze matching to place task by rats with neurotoxic lesions of the thalamic nucleus medialis dorsalis. This test of spatial working memory also entails learning a task rule that is contrary to the animals’ innate preference. The rats next performed the same matching task over different retention delays. Finally, they were trained on a reversal of the task rule, i.e., to nonmatch to place. Although the lesions produced a clear acquisition impairment on the matching task, there was no evidence of a loss of working memory. A series of control tasks found no appreciable effect on a conditioned cue preference task or on open field activity. The pattern of results shows that medialis dorsalis lesions lead to a selective increase in perseverative behavior that can retard task acquisition. This perseverative deficit closely resembles that observed after prefrontal damage in rats, strongly indicating dysfunction in a common system.

Publisher Summary This chapter reviews the anatomic connectivity of the centromedian–parafascicular (CM–Pf) complex, its role in the pathophysiology of movement disorders, and describe the relationship between anatomic stereotactic planning, and surgical and clinical outcome. Macroscopically, the dorsomedial thalamus is surrounded by the lamella medialis on its anterior, lateral, and inferior boundaries. Its length is 18–20 mm according to the distance between the anterior third of the massa intermedia and the habenular commissural plane. The thalamic central gray represents its medial boundary and because of its extension and size, the medial thalamus is commonly known as the nuclear medial region or medial territorium. The CM–Pf complex may play a key role in alleviating L-DOPA-induced involuntary movements. The effect of the DBS of the CM–Pf complex, as well as the effect of selective lesions, might depend on its impact on different neuronal substrates within the CM–Pf complex. The neuronal degeneration in the CM–Pf complex, which commonly occurs in PD patients, may affect preferentially some neuronal subpopulations, and this might modify the effects of the DBS.

N. A. has been amnesic since 1960 when he sustained a penetrating stab wound to the region of the left dorsomedial thalamus. The amnesia occurs as a strikingly circumscribed disorder in an intelligent (IQ = 124) individual without other cognitive dysfunction. Here, we attempt to characterize the nature of this amnesic disorder as revealed in daily activities, conversations, and personality. These observations are considered in the context of current views about the nature of normal memory and its neurological foundations.

Resume Des lesions bilaterales de l'amygdale pratiquees a un âge precoce (7–8 jours ou 25 jours): (1) entrainent une augmentation importante de la proportion des rats presentant a l'âge adulte un comportement d'agression vis-a-vis de la Souris (par exemple: amygdalectomie a 7–8 jours = 90% de rats tueurs compares aux 9% de tueurs chez les temoins operes); (2) reduisent nettement l'efficacite des contacts sociaux precoces avec la Souris, qui ont normalement pour effet de prevenir le developpement de la conduite agressive (72% de tueurs); (3) reduisent, chez le rat prive de ses bulbes olfactifs, l'efficacite des interactions sociales entre congeneres, qui ont egalement pour effet de prevenir le plus souvent l'apparition d'une agressivite interspecifique (59% de tueurs compares aux 7% chez les rats bulbectomises non amygdalectomises). Les interactions sociales entre rats bulbectomises restent efficaces a la suite d'une destruction bilaterale du thalamus dorsomedian.

The relationship between the nucleus medialis dorsalis thalami (DM) and the frontal lobe was investigated both anatomically and physiologically. Stimulation of DM evoked potentials of both long and short latency in frontal cortex. The long latency response waxed and waned but did not react to tetanic stimulation of the mesencephalic reticular formation or to anesthesia in the same manner as the classical recruiting response. The subcortical distribution of the sites producing the short latency response correlated well with the anatomical distribution of the pathway from DM to frontal cortex. The long latency response is suppressed by tetanic or paired stimulation of another DM point, the nuclei ventralis anterior or reticularis, and the septum, but the short latency response is unaffected by such stimuli. The long latency response seems to be the characteristic response of DM, and the short latency response appears to be due to stimulation of fibers of passage to frontal cortex. Stimulation of nuclei ventralis anterior, reticularis and septum can evoke long latency potentials in both DM and frontal cortex.

Resume La stimulation du thalamus dorsomedian ne delenche aucune reaction d'agression interspecifique chez le Rat. Qu'elle soit epileptogene ou non, cette stimulation thalamique entraine regulierement une inhibition de la reaction d'agression du rat tueur a l'egard de la Souris.

Rats with bilateral lesions of either the anterior, central, or posterior dorsomedial thalamus or with sham operations were compared on the acquisition of a food reinforced, tone-light, go/no-go discrimination task in an operant chamber. Rats with small lesions of the central portion of the medial thalamus (centered on the dorsomedial nucleus) were found to be deficient relative to rats with sham or small anterior medial thalamic lesions.

A group of 15 Long Evans rats with bilateral electrolytic lesions of the dorsomedial area of the thalamus (DMT) and a group consisting of 14 sham-operated and one normal rat were compared on maze activity, spontaneous alternation, runway acquisition and extinction, and response to a novel alley. The DMT-damaged rats were found to spontaneously alternate at chance level. Also, relative to controls, the experimental animals were slower to habituate locomotion in the maze and more resistant to extinction in the runway. The two groups did not differ significantly on response to novelty.

Eight rats with lesions of the dorsomedial thalamus and 10 rats with sham operations were compared on acquisition and subsequent reversals of a spatial discrimination. The rats with thalamic damage showed greater perseveration to the incorrect choices (p less than 0.002) and made fewer reversals (p less than 0.05) and more errors (p less than 0.02) during the 100 reversal trials following initial acquisition than did the sham-operated animals. The two groups did not differ on the original acquisition.

Focal field potentials and unit discharges of impulses evoked by low frequency (2–10/sec) stimulations of dorsomedial thalamus (DM) were simultaneously recorded with microelectrodes in the middle and inferior frontal gyri of the dorsal frontal granular cortex (FC) in the normal unanesthetized monkey. The depth profiles and sequences of responses of the FC evoked by the stimulations of DM were observed to be generally similar to the augmenting type of responses reported previously by others in the sensorimotor cortex of encephale isoleor paralyzed cat. Stimulations of DM evoked short latency (3.2–4.0 msec) negative waves at a depth of 0.6–1.7 mm and correlated positive waves on the surface of the FC. Additional waves of alternating polarity succeeded the primary waves during augmenting sequences according to variations of stimulus strength and frequency. Unit discharges recorded with the same electrode simultaneously with field potentials revealed that a brief burst of 2–4 impulses occurred in association with each of the short latency deep negative waves evoked by repetitive stimuli. The latency of the earliest of the spikes of a burst was in the range of 6.5–9 msec. Following the burst of spikes, there was a long period of absence of spikes in each response. Surface corticograms of FC and nearby precentral cortex revealed that the evoked responses were highly pronounced and restricted to the frontal granular cortex and did not spread diffusely to the agranular cortex. Only a prolonged (40–60 sec) stimulation caused a synchronizing tendency in the corticogram of the agranular area. Furthermore, the evoked potentials in the corticogram of FC were presently only during quiet wakeful states, and became highly disorganized and almost indecipherable during states of synchronizing EEG and decreased consciousness as in natural slow-wave sleep or under Nembutal anesthesia. From these results, it is concluded that the dorsomedial thalamus is organized more like a specific thalamic nucleus to the frontal association cortex, and less like an integral part of the diffuse projection system.

This study examined the effects of dorsomedial thalamic lesions on spontaneous alternation, learning, and reversal of spatial and nonspatial discriminations. Animals with thalamic damage, primarily involving the dorsomedial and periventricular nuclei, were impaired in learning and reversal of both brightness and tactile discriminations, but were not deficient in learning or 2 subsequent reversals of a spatial discrimination. Spontaneous alternation behavior was also unaffected by the lesion. It is suggested that although dorsomedial thalamic structures may be involved in nonspatial discrimination learning, they are not part of the neural apparatus underlying reversal or alternation behavior.