Thalamocortical Connections between the Mediodorsal Nucleus of the Thalamus and Prefrontal Cortex in the Human Brain: A Diffusion Tensor Tractographic Study

PURPOSE: The elucidation of thalamocortical connections between the mediodorsal nucleus (MD) of thalamus and the prefrontal cortex (PFC) is important in the clinical fields of neurorehabilitation and psychiatry. However, little is known about these connections in human brain. We attempted to identify and investigate the anatomical characteristics of the thalamocortical connection between MD and PFC in human brain using diffusion tensor tractography (DTT). MATERIALS AND METHODS: Thirty-two healthy volunteers were recruited for this study. Diffusion tensor images were scanned using a 1.5-T. A seed region of interest was placed at the MD of the thalamus on coronal images, and target regions of interest were placed on the dorsolateral prefrontal cortex (DLPFC), the ventrolateral prefrontal cortex (VLPFC), and the orbitofrontal cortex (OFC), respectively. The three thalamocortical connections found were reconstructed using Functional Magnetic Resonance Imaging of the Brain (FMRIB) software. RESULTS: The three thalamocortical connections were arranged in subcortical white matter in the following order from upper to lower levels: the DLPFC, the VLPFC, and the OFC. In terms of fractional anisotropy and mean diffusivity values, no significant differences were observed between the DLPFC, VLPFC and OFC (p>0.05). In contrast, the OFC tract volume was higher than those of the DLPFC and the VLPFC (p<0.05). CONCLUSION: Three thalamocortical connections were reconstructed between MD and PFCs in human brain using DTT. We believe that the results of this study would be helpful to clinicians in treating frontal network syndrome and psychiatric diseases.

Functional mapping of the cardiorespiratory effects of dorsal and median raphe nuclei in the rat

The dorsal (DRN) and median (MRN) raphe nuclei are important sources of serotonergic innervation to the forebrain, projecting to sites involved in cardiovascular regulation. These nuclei have been mapped using electrical stimulation, which has the limitation of stimulating fibers of passage. The present study maps these areas with chemical stimulation, investigating their influence on cardiorespiratory parameters. Urethane-anesthetized (1.2 g/kg, iv) male Wistar rats (280-300 g) were instrumented for pulsatile and mean blood pressure (MBP), heart rate, renal nerve activity, and respiratory frequency recordings. Microinjections of L-glutamate (0.18 M, 50-100 nl with 1 percent Pontamine Sky Blue) were performed within the DRN or the MRN with glass micropipettes. At the end of the experiments the sites of microinjection were identified. The majority of sites within the MRN (86.1 percent) and DRN (85.4 percent) evoked pressor responses when stimulated (DRN: deltaMBP = +14.7 ± 1.2; MRN: deltaMBP = +13.6 ± 1.3 mmHg). The changes in renal nerve activity and respiratory rate caused by L-glutamate were +45 ± 11 and +42 ± 9 percent (DRN; P < 0.05 percent), +40 ± 10 and +29 ± 7 percent (MRN, P < 0.05), respectively. No significant changes were observed in saline-microinjected animals. This study shows that: a) the blood pressure increases previously observed by electrical stimulation within the raphe are due to activation of local neurons, b) this pressor effect is due to sympathoexcitation because the stimulation increased renal sympathetic activity but did not produce tachycardia, and c) the stimulation of cell bodies in these nuclei also increases the respiratory rate.

Right Anterior Thalamic Infarction Presenting Only with Cognitive Dysfunction

A 60 year-old right-handed man developed a sudden inability to find his way home from work. Neurologic examina-tions revealed no focal neurological deficit. Neuropsychological tests showed a memory deficit especially in the visu-ospatial domain along with visuospatial and frontal-executive dysfunction. A brain MRI revealed a small but discrete lesion in the right thalamus. The majority of the lesion was confined to the dorsomedial nucleus. These results suggest that a small unilateral thalamic infarction affecting the anterior area may be sufficient to produce "strategic-infarct dementia" without focal neurological deficit.

Right Anterior Thalamic Infarction Presenting Only with Cognitive Dysfunction

A 60 year-old right-handed man developed a sudden inability to find his way home from work. Neurologic examina-tions revealed no focal neurological deficit. Neuropsychological tests showed a memory deficit especially in the visu-ospatial domain along with visuospatial and frontal-executive dysfunction. A brain MRI revealed a small but discrete lesion in the right thalamus. The majority of the lesion was confined to the dorsomedial nucleus. These results suggest that a small unilateral thalamic infarction affecting the anterior area may be sufficient to produce "strategic-infarct dementia" without focal neurological deficit.

Response of Hypothalamic Hypophyseal Hormones to Stimulation and Lesion in the Thalamus and Hypothalamus

Plasma levels of growth hormone(GH), luteinizing hormone(LH) and cortisol were determined by radioimmunoassay following radiofrequency(RF) stimulation or coagulation of various nuclei in thalamus and hypothalamus. RF stimulation or coagulation of many nuclei in thalamus and hypothalamus consisted of pulvinar and dorsomedial nucleus in thalamus and anterior and posterior hypothalamic nuclei in hypothalamus. Anterior thalamic stimulation resulted in highly significant increase of plasma LH, GH, cortisol and TH levels. However thalamic stimulation resulted no change in the level of various plasma hormones. Hypothalamic lesion produced significantly decreased plasma LH, GH and cortisol levels. Plasma cortisol and LH levels were highest 2 hours after stimulation while GH levels did not increased until 6 hours and TH until 72 hours respectively after stimulation. The significant difference in latency for beginning of hormone secretion suggests that GH, cortisol and LH may be controlled by several separate neuronal networks. Plasma GH and cortisol levels were lowest 72 hrs after coagulation of the anterior hypothalamic area, while GH, cortisol and LH levels did not change following stimulation or coagulation of posterior hypothalamic nucleus and thalamic nucldi. It was also noted that the anterior hypothalamic stimulation or coagulation caused increased or decreased in GH, cortisol, and LH than that observed from stimulation or coagulation of other hypothalamic and thalamic nuclei respectively.