Abstract
Claustrum is a thin sheet of gray matter located between external and extreme capsules of lentiform nucleus (basal ganglia). Functions of claustrum are still not clear. Positron emission tomography (PET) studies have been helpful in measuring the cerebral blood flow responses, as reflection of regional neuronal activity to various sensory stimuli. With PET it was seen that claustrum of healthy males displayed one of the highest activity with visual sexual stimuli.Bilateral activation of claustrum was seen to be involved in motivational processed, which direct behavior to a sexual goal.
Abstract
Introduction
Knowledge regarding the anatomical and functional aspects of claustrum is scanty. Still in our latest editions of textbooks of anatomy we cannot find its functions. Claustrum is a thin sheet of gray matter located between external and extreme capsules of Lentiform nucleus. It is grouped in basal nuclei, and consists of at least two structurally and functionally distinct zones; Insular claustrum and temporal or endopiriform claustrum.1 The ventrally situated part is endopiriform; whereas insular part is dorsally placed. Endopiriform claustrum originates from ventral pallium, the insular claustrum originates from both lateral and ventral pallial portions.2,3
We know most of the connections and functions of rest of the basal nuclei but Claustrum remains mysterious. To solve this mystery a review was done of the latest research works.
Ultrastructure of Claustrum
Cat's dorsal claustrum (insular) was studied by electron microscopy and by anterograde and retrograde tracer techniques. It receives a convergent retinoptic projection from several visual cortical areas. The commonest cell type in the claustrum was a neuron with large spiny dendrites and axon that leaves the cell after giving off local collaterals. There were also cells with beaded dendrites and a locally arborizing axon. Electron microscopy of the claustrum after ablation of the visual cortex showed degenerating type 1-axon terminals synapsing on spiny and beaded dendrites, suggesting a direct cortical input to both cell types. The visual claustrum projects back to the visual cortex, to same areas from which it receives an input. The claustrocortical axons terminate in all cortical layers.4
Although all cerebral cortical areas are reciprocally connected with the claustrum, but the posterior part of the claustrum is mainly connected to two main cortical related zones, sensorimotor and visoauditory. Between these two zones only scanty overlap was observed.5-7
All auditory areas have reciprocal connections with ipsilateral and contralateral claustrum. Main projection is in intermediate part of claustrum.8
The ventral part of claustrum is connected with limbic system.9 The dorsal insular part has reciprocal connections with the insular cortex. It is also connected to many regions of neocortex.10,11 Cat's insular cortex and claustrum were investigated with horseradish peroxidase retrograde technique. Their findings confirm the previous view that claustrum projects to most regions of cerebral cortex and also insular cortex.12 Visual cortex received considerable number of claustral projections.13,14
Functions of Claustrum
Functions of claustrum are still not clear. Differences in morphology and the cellular structure of two parts of the claustrum may suggest differences in functions of two parts of the nucleus. One method of assessing the function of claustrum is through Positron emission tomographic studies, as this helps to measure the cerebral blood flow responses, as reflections of regional neuronal activity, to various sensory stimuli. Second method is to work out the functions through its connections with different parts of brain.
Evidence of role of Claustrum in Emotions and Sexual Arousal
In a study Positron emission tomography was used to investigate responses of regional blood flow in healthy males represented with visual sexual stimuli of graded intensity. The claustrum displayed one of the highest activity. The additional activations were recorded in right insular, paralimbic areas, striatum and the posterior hypothalamus.13,15 This study confirms the results of previous study of Stoleru et al.16 in which they proposed a behavioral model of "sexual arousal" comprising of four coordinated components i.e., cognitive, emotional, motivational and physiological. Briefly the cognitive component comprises a process of appraisal through which a stimulus is categorized as a sexual incentive. The emotional component includes the specific hedonic quality of sexual arousal i.e., the pleasure associated with arising arousal and with perception of specific bodily changes such as penile tumescence. The motivational component comprises the process that direct behavior to a sexual goal, including the perceived urge to express overt sexual behavior. Physiological component include various responses (e.g. cardiovascular, respiratory, genital) leading subject to a state of physiological readiness for sexual behavior. The highly significant bilateral activation of claustrum was one of the striking findings, which was seen to be involved in motivational processes.17 There is further evidence for the role of claustrum in emotional and motivational responses in rats16 and in man.18
Arnow et al19 in a study employed functional MRI to examine the relationship between brain activation and sexual arousal. Strong activations specially associated with penile turgidity were observed in right subinsular regions including the claustrum.19 In addition to above, more evidence of claustrum in sexual arousal is through its connections with surrounding brain areas. Penile erection and subjective sexual arousal were assessed by bold functional MRI, using erotic films as visual stimuli. It was observed that cingulated gyrus and insula were significantly activated.19,20 Claustrum is also connected to limbic system. The connecting neurons are mainly localized in anterior and central parts of claustrum. So there is a role of claustrum in control of emotions, behavior and drive.21,22
It is thus concluded that claustrum has reciprocal connections with all cortical areas. Insular cortex and visual cortex received considerable number of claustral projections. Cingulate cortex also receives inputs from claustrum. Insula and cingulated gyrus are widely thought to be involved in regulations of emotions; so claustrum was thought to be involved in regulation of emotions. By Positron emission tomography and MRI it was seen that claustrum showed highest activations with visual sexual stimuli. The highly significant bilateral activation of the claustrum was one of the striking findings, which was seen to be involved in motivational processes.
Introduction
Knowledge regarding the anatomical and functional aspects of claustrum is scanty. Still in our latest editions of textbooks of anatomy we cannot find its functions. Claustrum is a thin sheet of gray matter located between external and extreme capsules of Lentiform nucleus. It is grouped in basal nuclei, and consists of at least two structurally and functionally distinct zones; Insular claustrum and temporal or endopiriform claustrum.1 The ventrally situated part is endopiriform; whereas insular part is dorsally placed. Endopiriform claustrum originates from ventral pallium, the insular claustrum originates from both lateral and ventral pallial portions.2,3
We know most of the connections and functions of rest of the basal nuclei but Claustrum remains mysterious. To solve this mystery a review was done of the latest research works.
Ultrastructure of Claustrum
Cat's dorsal claustrum (insular) was studied by electron microscopy and by anterograde and retrograde tracer techniques. It receives a convergent retinoptic projection from several visual cortical areas. The commonest cell type in the claustrum was a neuron with large spiny dendrites and axon that leaves the cell after giving off local collaterals. There were also cells with beaded dendrites and a locally arborizing axon. Electron microscopy of the claustrum after ablation of the visual cortex showed degenerating type 1-axon terminals synapsing on spiny and beaded dendrites, suggesting a direct cortical input to both cell types. The visual claustrum projects back to the visual cortex, to same areas from which it receives an input. The claustrocortical axons terminate in all cortical layers.4
Although all cerebral cortical areas are reciprocally connected with the claustrum, but the posterior part of the claustrum is mainly connected to two main cortical related zones, sensorimotor and visoauditory. Between these two zones only scanty overlap was observed.5-7
All auditory areas have reciprocal connections with ipsilateral and contralateral claustrum. Main projection is in intermediate part of claustrum.8
The ventral part of claustrum is connected with limbic system.9 The dorsal insular part has reciprocal connections with the insular cortex. It is also connected to many regions of neocortex.10,11 Cat's insular cortex and claustrum were investigated with horseradish peroxidase retrograde technique. Their findings confirm the previous view that claustrum projects to most regions of cerebral cortex and also insular cortex.12 Visual cortex received considerable number of claustral projections.13,14
Functions of Claustrum
Functions of claustrum are still not clear. Differences in morphology and the cellular structure of two parts of the claustrum may suggest differences in functions of two parts of the nucleus. One method of assessing the function of claustrum is through Positron emission tomographic studies, as this helps to measure the cerebral blood flow responses, as reflections of regional neuronal activity, to various sensory stimuli. Second method is to work out the functions through its connections with different parts of brain.
Evidence of role of Claustrum in Emotions and Sexual Arousal
In a study Positron emission tomography was used to investigate responses of regional blood flow in healthy males represented with visual sexual stimuli of graded intensity. The claustrum displayed one of the highest activity. The additional activations were recorded in right insular, paralimbic areas, striatum and the posterior hypothalamus.13,15 This study confirms the results of previous study of Stoleru et al.16 in which they proposed a behavioral model of "sexual arousal" comprising of four coordinated components i.e., cognitive, emotional, motivational and physiological. Briefly the cognitive component comprises a process of appraisal through which a stimulus is categorized as a sexual incentive. The emotional component includes the specific hedonic quality of sexual arousal i.e., the pleasure associated with arising arousal and with perception of specific bodily changes such as penile tumescence. The motivational component comprises the process that direct behavior to a sexual goal, including the perceived urge to express overt sexual behavior. Physiological component include various responses (e.g. cardiovascular, respiratory, genital) leading subject to a state of physiological readiness for sexual behavior. The highly significant bilateral activation of claustrum was one of the striking findings, which was seen to be involved in motivational processes.17 There is further evidence for the role of claustrum in emotional and motivational responses in rats16 and in man.18
Arnow et al19 in a study employed functional MRI to examine the relationship between brain activation and sexual arousal. Strong activations specially associated with penile turgidity were observed in right subinsular regions including the claustrum.19 In addition to above, more evidence of claustrum in sexual arousal is through its connections with surrounding brain areas. Penile erection and subjective sexual arousal were assessed by bold functional MRI, using erotic films as visual stimuli. It was observed that cingulated gyrus and insula were significantly activated.19,20 Claustrum is also connected to limbic system. The connecting neurons are mainly localized in anterior and central parts of claustrum. So there is a role of claustrum in control of emotions, behavior and drive.21,22
It is thus concluded that claustrum has reciprocal connections with all cortical areas. Insular cortex and visual cortex received considerable number of claustral projections. Cingulate cortex also receives inputs from claustrum. Insula and cingulated gyrus are widely thought to be involved in regulations of emotions; so claustrum was thought to be involved in regulation of emotions. By Positron emission tomography and MRI it was seen that claustrum showed highest activations with visual sexual stimuli. The highly significant bilateral activation of the claustrum was one of the striking findings, which was seen to be involved in motivational processes.
References
1. Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, Ferguson MWJ. Cerebral cortex. In: Gray's anatomy. Edinburgh: Churchill Livingston, 1995, p.1149.
2. Rebelt C, Algo A, Blanco-santiago R., Mendizabal-Zubaiga J, Fuentes M, Bueno-Lopez JL. Neuroepithelial origin of the insular and endopiriform parts of the claustrum. Brain Res Bull 2002;57:495-7.
3. Bayer SA, Aitman J. Development of endopiriform nucleus and claustrum in the rat brain. Neuroscience 1991;45:391-421.
4. Maciejewska B, Morys J, Berdel B, Narkiewicz O. Insular claustrum of the dog - a morphometric investigation of cellular structure. Folia Morphol (Warsz) 1994;53:209-19.
5. Levay S, Sherk H. The visual claustrum of cat. Structure and connections. J Neurosci 1981;1 956-80.
6. Pearson RCA, Brodal P, Gatter KC, Powell TPS. The organization of the connections between the cortex and the claustrum in the monkey. Brain Res 1982;234:435-41.
7. Sherk H. The claustrum and cerebral cortex. In: Jones EG., Peters A.(ed.). Cerebral Cortex. Vol. 5, New York: Plenum 1986;467-99.
8. Sadowski M, Morys J, Jakubowska-Sadowska K, Narkiewicz O. Rat's claustrum shows two main cortical related zones. Brain Res 1997;756:147-52.
9. Beneyto M. Prieto JJ. Connections of the auditory cortex with the claustrum and the endopiriform nucleus in the cat. Brain Res Bull 2001;54:485-98.
10. Kowianski P, Dziwiatkowski J, Kowianska J, Mory SJ. Comparative anatomy of the claustrum in selected species: a morphometeric analysis. Brain Behav Evol 1999; 53: 44-54.
11. Mesulam MM, Mufson EJ. Insula of the old monkey III: Efferent cortical out put and comments on function. JComp Neuro 1982;212:38-52.
12. Augustine JR. The insular lobe in primates including humans. Neural Res 1985; 7:2-10.
13. Banati RB, Goerres GW, Tjoa C, Aggleton JP, Grasby P. The functional anatomy of visual tactile integration in man: a study using Positron emission tomography. Neuropsychologia 2000;38:115-24.
14. Carey RG, Neal TL. The rat claustrum: afferent and efferent connections with visual cortex. Brain Res 1985;329:185-93.
15. Redoute J, Stoleru S, Gregorie MC, Costes N, Cintti L, Lavenne F, et al. Brain processing of visual sexual stimuli in human males. Hum-Brain processing of visual sexual stimuli in human males. Hum-Brain Mapp 2001;1:162-77
16. Stoleru S, Gregoire MC, Gerard D, Decety J, Laferge E, Cinotti L, et al. Neuroanatomical correlates of visually evoked sexual arousal in human males. Arch Sex Behav 1999;28:1-21.
17. Hadjkhani N, Roland PE. Cross model transfer of information between tactile and visual representations in human brain Positron emission tomographyic study. J Neurosci 1998;18:1072-84.
18. Hamamura T, Ichimaru Y, Fibiger HC. Amphetamin sensitization enhances regional c-fos expression produced by conditioned fear. Neuroscience 1997;76:1097-103.
19. Arnow BA, Desmond JE, Banner LL, Glover GH, Solomon A, Polan ML, et al. Brain activation and sexual arousal in healthy heterosexual males. Brain 2002;125:1014-23.
20. Park K, Seo JJ, Kang HK, Rju SB, Kim HH, Jeong GW. A new potential of blood oxygenation level dependent (Bold) functional MRI for evaluating cerebral centers of penile erection.Int J Impot Res 2001;13:73-81
21. Bocher M, Chisin R, Parag Y, Freedman N, Meir Weil Y, Laster H, et al. Cerebral activation associated with sexual arousal in response to a pornographic clip: A 150-H20 PET study in heterosexual men. Neuroimage 2001;14:105-17.
22. Rauch SL, Shin LM, Dougherty DD, Alpert NM, Orr Sp, Lasko M, et al. Neural activation during sexual and competitive arousal in healthy men.Psychiatry Res 1999;91:1-10.
