- Email: [email protected]
Motor Control: Parietal Stimulation Prevents Voluntary Hand Movement
Current Biology
Dispatches 2. Thompson, D.W. (1917). On Growth and Form (Cambridge: Cambridge University Press).
and molecular dynamics. Semin. Cell Dev. Biol. 67, 153–160.
3. Heisenberg, C.P. (2017). D’Arcy Thompson’s ‘on Growth and form’: From soap bubbles to tissue self-organization. Mech. Dev. 145, 32–37.
9. Devenport, D. (2014). The cell biology of planar cell polarity. J. Cell Biol. 207, 171–179.
4. Plateau, J. (1873). Statique Experimentale et Theorique Des Liquides Soumis aux Seules Forces Moleculaires (Paris: Gauthier-Villars). 5. Lecuit, T., and Lenne, P.F. (2007). Cell surface mechanics and the control of cell shape, tissue patterns and morphogenesis. Nat. Rev. Mol. Cell Biol. 8, 633–644. 6. Hayashi, T., and Carthew, R.W. (2004). Surface mechanics mediate pattern formation in the developing retina. Nature 431, 647–652. 7. Gibson, M.C., Patel, A.B., Nagpal, R., and Perrimon, N. (2006). The emergence of geometric order in proliferating metazoan epithelia. Nature 442, 1038–1041. 8. Yu, J.C., and Fernandez-Gonzalez, R. (2017). Quantitative modelling of epithelial morphogenesis: integrating cell mechanics
14. Fletcher, A.G., Osterfield, M., Baker, R.E., and Shvartsman, S.Y. (2014). Vertex models of epithelial morphogenesis. Biophys. J. 106, 2291–2304.
10. Martin, A.C., Kaschube, M., and Wieschaus, E.F. (2009). Pulsed contractions of an actinmyosin network drive apical constriction. Nature 457, 495–499.
15. Condic, M.L., Fristrom, D., and Fristrom, J.W. (1991). Apical cell shape changes during Drosophila imaginal leg disc elongation: a novel morphogenetic mechanism. Development 111, 23–33.
11. Plageman, T.F., Jr., Chung, M.I., Lou, M., Smith, A.N., Hildebrand, J.D., Wallingford, J.B., and Lang, R.A. (2010). Pax6-dependent Shroom3 expression regulates apical constriction during lens placode invagination. Development 137, 405–415.
16. Rupprecht, J.F., Ong, K.H., Yin, J., Huang, A., Dinh, H.H., Singh, A.P., Zhang, S., Yu, W., and Saunders, T.E. (2017). Geometric constraints alter cell arrangements within curved epithelial tissues. Mol. Biol. Cell 28, 3582–3594.
12. Kim, H.Y., Varner, V.D., and Nelson, C.M. (2013). Apical constriction initiates new bud formation during monopodial branching of the embryonic chicken lung. Development 140, 3146–3155.
17. Irvine, K.D., and Wieschaus, E. (1994). Cell intercalation during Drosophila germband extension and its regulation by pair-rule segmentation genes. Development 120, 827–841.
13. Misra, M., Audoly, B., Kevrekidis, I.G., and Shvartsman, S.Y. (2016). Shape transformations of epithelial shells. Biophys. J. 110, 1670–1678.
18. Jodoin, J.N., and Martin, A.C. (2016). Abl suppresses cell extrusion and intercalation during epithelium folding. Mol. Biol. Cell 27, 2822–2832.
Motor Control: Parietal Stimulation Prevents Voluntary Hand Movement Axel Lindner Department of Psychiatry and Psychotherapy, University Hospital Tu¨bingen, Calwerstraße 14, 72076 Tu¨bingen, Germany Correspondence: [email protected] https://doi.org/10.1016/j.cub.2018.09.001
Inhibition of action is commonly attributed to frontal cortex. A new study shows that intra-surgical stimulation of human posterior parietal cortex selectively prevents the initiation and execution of voluntary movement of the contralateral hand. Making the right move at the right time is crucial for humans and animals alike. I am constantly reminded of this simple truth, for instance whenever trying to cross a busy street. In such situations I usually plan my way across the street in advance. Yet, my action plan needs to be withheld until there is a large enough traffic gap; and, if something unexpected happens, for example an approaching car suddenly accelerates, I might need to stop my plan at the very last second. What is going on in peoples’ brains in such situations? How does our central nervous system realize the proactive and reactive inhibition of voluntary movement needed in everyday life? While we already have gained a quite decent understanding of how the brain
brings about goal-directed movement, much less is known about the ways it prevents specific actions and why. In this issue of Current Biology, Desmurget et al. [1] report that intra-surgical stimulation of posterior parietal cortex does inhibit the initiation and execution of voluntary hand movement with high selectivity. Their results provide novel clues about how this part of the human brain could assist us in achieving optimal performance through action inhibition. The stimulation technique used by Desmurget et al. [1] is referred to as direct electrical stimulation. Direct electrical stimulation is first of all a clinical tool, which can be used to identify areas that subserve important functions, such as
R1200 Current Biology 28, R1190–R1211, October 22, 2018 ª 2018 Elsevier Ltd.
language. Such functional mapping can help neurosurgeons to reduce postoperative deficits in their patients whenever there is need to resect brain tissue [2,3]. For instance, in case of Desmurget et al.’s [1] patients, intrasurgical mapping was required to inform the neurosurgeon prior to tumor removal. Direct electrical stimulation provides researchers with rare and valuable insights into human brain function through its direct — though artificial — interference with neuronal processing [2,3]. Direct electrical stimulation is widely known through the work of Wilder Penfield and Edwin Boldrey [4] in the 1930s. Penfield and Boldrey used direct electrical stimulation for a clinical
Current Biology
Dispatches purpose, but it additionally allowed them to produce the most detailed maps of motor and somatosensory representations in human cerebral cortex at the time. Their graphical illustration of these maps, the ‘sensory and motor homunculus’, is familiar to many people. The motor homunculus can be considered a cornerstone in the investigation of motor functions of the human brain. It was based on the observation of direct-electricalstimulation-induced ‘positive movement effects’ in the stimulated patient. Penfield and Boldrey noticed, however, that, apart from such positive motor effects, stimulation of certain areas could inhibit ongoing speech. Since then, such directelectrical-stimulation-induced inhibitory effects on speech and on other bodily movement have been studied in great detail and the regions in which these effects could be triggered are referred to as ‘negative motor areas’ [5]. Is the function of these negative motor areas truly inhibitory? Could it be that direct electrical stimulation effectively perturbs (locally or remotely) the processing within these areas whose primary role is rather excitatory? While this cannot be ruled out with certainty [2,3], Filevich et al. [6] provided compelling arguments in favor of a true inhibitory role of negative motor areas in a recent review. Interestingly, all of the negative motor areas reported in their review were restricted to frontal cortex (Figure 1, blue circles). Moreover, the objective measures of direct-electricalstimulation-induced negative motor effects in these areas had been reported only for ongoing movements, and not for movement initiation [6]. The new study by Desmurget et al. [1] differs from these earlier works on negative motor areas in various respects. Most strikingly, their study does report a negative motor area in the posterior part of the brain, namely in superior parietal lobule, next to the convexity of the intraparietal sulcus (Figure 1, red squares). Moreover, their study shows a high degree of effector specificity: Parietal stimulation only led to an inhibition of voluntary movement of the hand that was contralateral to the direct electrical stimulation sites. Stimulation did not affect movements of the ipsilateral hand, movements of the leg, or speech. This
p
a
p
a
r
l
Parietal inhibition sites
Frontal inhibition site
Negative motor areas l Current Biology
Figure 1. Negative motor areas. All blue circles on the ‘glass brain’ point to negative motor areas in frontal cortex, as were reviewed by Filevich et al. [6]. Red squares designate the ‘new’ parietal inhibition sites reported by Desmurget et al. [1]. Red diamonds indicate their frontal control site. Blue lines intersect at the anterior commissure (a, anterior; p, posterior; l, left; r, right). Adapted with permission from [6].
result contrasted sharply with direct electrical stimulation of frontal ‘control’ sites (Figure 1, red diamonds): stimulation of the dorsal precentral gyrus and the posterior part of superior frontal gyrus inhibited ongoing movement across all effectors, as is often seen during frontal direct electrical stimulation. Finally, direct electrical stimulation at the parietal sites not only led to an inhibition of ongoing hand movements but also prevented patients from initiating such movements. This also differs from results for frontal areas, which foremost seem to be engaged in the stopping of already ongoing action programs [7]. What could be the functional contribution of this ‘new’ negative motor area in posterior parietal cortex? Before addressing this question, it is worthwhile to briefly review the functional properties of nearby areas in posterior parietal cortex. Electrophysiological studies in monkeys as well as human imaging experiments document the contribution of these areas to the planning and control of actions, including goal-directed movements of the upper limbs [8,9]. The fact that the latter parietal areas exhibit a high degree of
effector-specificity and predominantly code for movement of the contralateral limb [8,9] corresponds well with the pattern of results reported by Desmurget et al. [1]. So does the result of a recent fMRI study [10], which showed that overlapping regions in posterior parietal cortex not only become active when subjects plan goaldirected finger movements, but also when they proactively plan to avoid such movements. Finally, posterior parietal cortex can represent alternative hand action plans [11], and plans are weighted according to their behavioral import [12]. These latter characteristics further suggest a role of posterior parietal cortex in action selection, as they allow the highlighting of promising action opportunities [8,13]. The inhibition of inappropriate actions or action inopportunities would perfectly complement this putative parietal function [10] — as if reflecting the opposite side of the same coin (compare [14]). It is important to stress that the aforementioned types of prospective action inhibition are not only a theoretical construct. The investigation of human corticospinal excitability has revealed direct physiological signs of prospective
Current Biology 28, R1190–R1211, October 22, 2018 R1201
Current Biology
Dispatches inhibition during action preparation, such as to prevent impulsive responses, to delay the execution of motor plans until the right moment, or to inhibit competing or undesirable behavioral options [15,16]. Posterior parietal cortex, and in particular the negative motor area described by Desmurget et al. [1], may be well suited to mediate such effects [17]. Additional research is needed to critically investigate these ideas and to link them to neuropsychiatric phenomena [18]. For instance, given the aforesaid, it may not be surprising that parietal lesions can cause involuntary limb movements. This is the case in the posterior variant of the alien hand syndrome [19], which well might reflect patients’ inability to inhibit action opportunities [20]. Clearly, the study of Desmurget et al. [1] provides ‘stimulating’ clues that will fuel future investigations about how posterior parietal cortex could support us in realizing an optimal course of action through both the excitation and inhibition of goal-directed movement.
REFERENCES 1. Desmurget, M., Richard, N., Beuriat, P.-A., Szathmari, A., Mottolese, C., Duhamel, J.-R., and Sirigu, A. (2018). Selective inhibition of volitional hand movements after stimulation of the dorsoposterior parietal cortex in humans. Curr. Biol. 28, 3303–3309.
2. Borchers, S., Himmelbach, M., Logothetis, N., and Karnath, H.O. (2011). Direct electrical stimulation of human cortex - the gold standard for mapping brain functions? Nat. Rev. Neurosci. 13, 63–70. 3. Desmurget, M., and Sirigu, A. (2015). Revealing humans’ sensorimotor functions with electrical cortical stimulation. Philos. Trans. R. Soc. Lond. B 370, 20140207. 4. Penfield, W., and Boldrey, E. (1937). Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation. Brain 60, 389–443. 5. Lu¨ders, H.O., Dinner, D.S., Morris, H.H., Wyllie, E., and Comair, Y.G. (1995). Cortical electrical stimulation in humans. The negative motor areas. Adv. Neurol. 67, 115–129. 6. Filevich, E., Ku¨hn, S., and Haggard, P. (2012). Negative motor phenomena in cortical stimulation: implications for inhibitory control of human action. Cortex 48, 1251–1261. 7. Aron, A.R., Robbins, T.W., and Poldrack, R.A. (2014). Inhibition and the right inferior frontal cortex: one decade on. Trends Cogn. Sci. 18, 177–185. 8. Andersen, R.A., and Cui, H. (2009). Intention, action planning, and decision making in parietal-frontal circuits. Neuron 63, 568–583. 9. Culham, J.C., Cavina-Pratesi, C., and Singhal, A. (2006). The role of parietal cortex in visuomotor control: what have we learned from neuroimaging? Neuropsychologia 44, 2668–2684. 10. Lindner, A., Iyer, A., Kagan, I., and Andersen, R.A. (2010). Human posterior parietal cortex plans where to reach and what to avoid. J. Neurosci. 30, 11715–11725.
11. Klaes, C., Westendorff, S., Chakrabarti, S., and Gail, A. (2011). Choosing goals, not rules: deciding among rule-based action plans. Neuron 70, 536–548. 12. Iyer, A., Lindner, A., Kagan, I., and Andersen, R.A. (2010). Motor preparatory activity in posterior parietal cortex is modulated by subjective absolute value. PLoS Biol. 8, e1000444. 13. Cisek, P. (2012). Making decisions through a distributed consensus. Curr. Opin. Neurobiol. 22, 927–936. 14. Mostofsky, S.H., and Simmonds, D.J. (2008). Response inhibition and response selection: two sides of the same coin. J. Cogn. Neurosci. 20, 751–761. 15. Duque, J., Greenhouse, I., Labruna, L., and Ivry, R.B. (2017). Physiological markers of motor inhibition during human behavior. Trends Neurosci. 40, 219–236. 16. Bestmann, S., and Duque, J. (2016). Transcranial magnetic stimulation: decomposing the processes underlying action preparation. Neuroscientist 22, 392–405. 17. Rathelot, J.A., Dum, R.P., and Strick, P.L. (2017). Posterior parietal cortex contains a command apparatus for hand movements. Proc. Natl. Acad. Sci. USA 114, 4255–4260. 18. Aron, A.R. (2011). From reactive to proactive and selective control: developing a richer model for stopping inappropriate responses. Biol. Psychiatry. 69, e55–e68. 19. Hassan, A., and Josephs, K.A. (2016). Alien hand syndrome. Curr. Neurol. Neurosci. Rep. 16, 73. 20. McBride, J., Sumner, P., Jackson, S.R., Bajaj, N., and Husain, M. (2013). Exaggerated object affordance and absent automatic inhibition in alien hand syndrome. Cortex 49, 2040–2054.
Sensory Biology: Structure of an Insect Chemoreceptor Yichen Luo and John R. Carlson* Dept. of Molecular, Cellular and Developmental Biology, Interdepartmental Neuroscience Program, Yale University, New Haven, CT 06520-8103, USA *Correspondence: [email protected] https://doi.org/10.1016/j.cub.2018.09.002
Odorant receptors detect a vast diversity of chemical compounds and underlie many aspects of life. The structure of insect odorant receptors, however, has remained unknown. A cryo-EM study now reveals an intriguing architecture. Twenty years have elapsed since the first insect odorant receptors were identified [1,2]. Odorant receptors may be the
largest family of ion channels in the animal kingdom: an enormous number of insect species have them, each species has
R1202 Current Biology 28, R1190–R1211, October 22, 2018 ª 2018 Elsevier Ltd.
many of them, and their sequences are highly divergent. The odorant receptors detect and discriminate among
Dispatches 2. Thompson, D.W. (1917). On Growth and Form (Cambridge: Cambridge University Press).
and molecular dynamics. Semin. Cell Dev. Biol. 67, 153–160.
3. Heisenberg, C.P. (2017). D’Arcy Thompson’s ‘on Growth and form’: From soap bubbles to tissue self-organization. Mech. Dev. 145, 32–37.
9. Devenport, D. (2014). The cell biology of planar cell polarity. J. Cell Biol. 207, 171–179.
4. Plateau, J. (1873). Statique Experimentale et Theorique Des Liquides Soumis aux Seules Forces Moleculaires (Paris: Gauthier-Villars). 5. Lecuit, T., and Lenne, P.F. (2007). Cell surface mechanics and the control of cell shape, tissue patterns and morphogenesis. Nat. Rev. Mol. Cell Biol. 8, 633–644. 6. Hayashi, T., and Carthew, R.W. (2004). Surface mechanics mediate pattern formation in the developing retina. Nature 431, 647–652. 7. Gibson, M.C., Patel, A.B., Nagpal, R., and Perrimon, N. (2006). The emergence of geometric order in proliferating metazoan epithelia. Nature 442, 1038–1041. 8. Yu, J.C., and Fernandez-Gonzalez, R. (2017). Quantitative modelling of epithelial morphogenesis: integrating cell mechanics
14. Fletcher, A.G., Osterfield, M., Baker, R.E., and Shvartsman, S.Y. (2014). Vertex models of epithelial morphogenesis. Biophys. J. 106, 2291–2304.
10. Martin, A.C., Kaschube, M., and Wieschaus, E.F. (2009). Pulsed contractions of an actinmyosin network drive apical constriction. Nature 457, 495–499.
15. Condic, M.L., Fristrom, D., and Fristrom, J.W. (1991). Apical cell shape changes during Drosophila imaginal leg disc elongation: a novel morphogenetic mechanism. Development 111, 23–33.
11. Plageman, T.F., Jr., Chung, M.I., Lou, M., Smith, A.N., Hildebrand, J.D., Wallingford, J.B., and Lang, R.A. (2010). Pax6-dependent Shroom3 expression regulates apical constriction during lens placode invagination. Development 137, 405–415.
16. Rupprecht, J.F., Ong, K.H., Yin, J., Huang, A., Dinh, H.H., Singh, A.P., Zhang, S., Yu, W., and Saunders, T.E. (2017). Geometric constraints alter cell arrangements within curved epithelial tissues. Mol. Biol. Cell 28, 3582–3594.
12. Kim, H.Y., Varner, V.D., and Nelson, C.M. (2013). Apical constriction initiates new bud formation during monopodial branching of the embryonic chicken lung. Development 140, 3146–3155.
17. Irvine, K.D., and Wieschaus, E. (1994). Cell intercalation during Drosophila germband extension and its regulation by pair-rule segmentation genes. Development 120, 827–841.
13. Misra, M., Audoly, B., Kevrekidis, I.G., and Shvartsman, S.Y. (2016). Shape transformations of epithelial shells. Biophys. J. 110, 1670–1678.
18. Jodoin, J.N., and Martin, A.C. (2016). Abl suppresses cell extrusion and intercalation during epithelium folding. Mol. Biol. Cell 27, 2822–2832.
Motor Control: Parietal Stimulation Prevents Voluntary Hand Movement Axel Lindner Department of Psychiatry and Psychotherapy, University Hospital Tu¨bingen, Calwerstraße 14, 72076 Tu¨bingen, Germany Correspondence: [email protected] https://doi.org/10.1016/j.cub.2018.09.001
Inhibition of action is commonly attributed to frontal cortex. A new study shows that intra-surgical stimulation of human posterior parietal cortex selectively prevents the initiation and execution of voluntary movement of the contralateral hand. Making the right move at the right time is crucial for humans and animals alike. I am constantly reminded of this simple truth, for instance whenever trying to cross a busy street. In such situations I usually plan my way across the street in advance. Yet, my action plan needs to be withheld until there is a large enough traffic gap; and, if something unexpected happens, for example an approaching car suddenly accelerates, I might need to stop my plan at the very last second. What is going on in peoples’ brains in such situations? How does our central nervous system realize the proactive and reactive inhibition of voluntary movement needed in everyday life? While we already have gained a quite decent understanding of how the brain
brings about goal-directed movement, much less is known about the ways it prevents specific actions and why. In this issue of Current Biology, Desmurget et al. [1] report that intra-surgical stimulation of posterior parietal cortex does inhibit the initiation and execution of voluntary hand movement with high selectivity. Their results provide novel clues about how this part of the human brain could assist us in achieving optimal performance through action inhibition. The stimulation technique used by Desmurget et al. [1] is referred to as direct electrical stimulation. Direct electrical stimulation is first of all a clinical tool, which can be used to identify areas that subserve important functions, such as
R1200 Current Biology 28, R1190–R1211, October 22, 2018 ª 2018 Elsevier Ltd.
language. Such functional mapping can help neurosurgeons to reduce postoperative deficits in their patients whenever there is need to resect brain tissue [2,3]. For instance, in case of Desmurget et al.’s [1] patients, intrasurgical mapping was required to inform the neurosurgeon prior to tumor removal. Direct electrical stimulation provides researchers with rare and valuable insights into human brain function through its direct — though artificial — interference with neuronal processing [2,3]. Direct electrical stimulation is widely known through the work of Wilder Penfield and Edwin Boldrey [4] in the 1930s. Penfield and Boldrey used direct electrical stimulation for a clinical
Current Biology
Dispatches purpose, but it additionally allowed them to produce the most detailed maps of motor and somatosensory representations in human cerebral cortex at the time. Their graphical illustration of these maps, the ‘sensory and motor homunculus’, is familiar to many people. The motor homunculus can be considered a cornerstone in the investigation of motor functions of the human brain. It was based on the observation of direct-electricalstimulation-induced ‘positive movement effects’ in the stimulated patient. Penfield and Boldrey noticed, however, that, apart from such positive motor effects, stimulation of certain areas could inhibit ongoing speech. Since then, such directelectrical-stimulation-induced inhibitory effects on speech and on other bodily movement have been studied in great detail and the regions in which these effects could be triggered are referred to as ‘negative motor areas’ [5]. Is the function of these negative motor areas truly inhibitory? Could it be that direct electrical stimulation effectively perturbs (locally or remotely) the processing within these areas whose primary role is rather excitatory? While this cannot be ruled out with certainty [2,3], Filevich et al. [6] provided compelling arguments in favor of a true inhibitory role of negative motor areas in a recent review. Interestingly, all of the negative motor areas reported in their review were restricted to frontal cortex (Figure 1, blue circles). Moreover, the objective measures of direct-electricalstimulation-induced negative motor effects in these areas had been reported only for ongoing movements, and not for movement initiation [6]. The new study by Desmurget et al. [1] differs from these earlier works on negative motor areas in various respects. Most strikingly, their study does report a negative motor area in the posterior part of the brain, namely in superior parietal lobule, next to the convexity of the intraparietal sulcus (Figure 1, red squares). Moreover, their study shows a high degree of effector specificity: Parietal stimulation only led to an inhibition of voluntary movement of the hand that was contralateral to the direct electrical stimulation sites. Stimulation did not affect movements of the ipsilateral hand, movements of the leg, or speech. This
p
a
p
a
r
l
Parietal inhibition sites
Frontal inhibition site
Negative motor areas l Current Biology
Figure 1. Negative motor areas. All blue circles on the ‘glass brain’ point to negative motor areas in frontal cortex, as were reviewed by Filevich et al. [6]. Red squares designate the ‘new’ parietal inhibition sites reported by Desmurget et al. [1]. Red diamonds indicate their frontal control site. Blue lines intersect at the anterior commissure (a, anterior; p, posterior; l, left; r, right). Adapted with permission from [6].
result contrasted sharply with direct electrical stimulation of frontal ‘control’ sites (Figure 1, red diamonds): stimulation of the dorsal precentral gyrus and the posterior part of superior frontal gyrus inhibited ongoing movement across all effectors, as is often seen during frontal direct electrical stimulation. Finally, direct electrical stimulation at the parietal sites not only led to an inhibition of ongoing hand movements but also prevented patients from initiating such movements. This also differs from results for frontal areas, which foremost seem to be engaged in the stopping of already ongoing action programs [7]. What could be the functional contribution of this ‘new’ negative motor area in posterior parietal cortex? Before addressing this question, it is worthwhile to briefly review the functional properties of nearby areas in posterior parietal cortex. Electrophysiological studies in monkeys as well as human imaging experiments document the contribution of these areas to the planning and control of actions, including goal-directed movements of the upper limbs [8,9]. The fact that the latter parietal areas exhibit a high degree of
effector-specificity and predominantly code for movement of the contralateral limb [8,9] corresponds well with the pattern of results reported by Desmurget et al. [1]. So does the result of a recent fMRI study [10], which showed that overlapping regions in posterior parietal cortex not only become active when subjects plan goaldirected finger movements, but also when they proactively plan to avoid such movements. Finally, posterior parietal cortex can represent alternative hand action plans [11], and plans are weighted according to their behavioral import [12]. These latter characteristics further suggest a role of posterior parietal cortex in action selection, as they allow the highlighting of promising action opportunities [8,13]. The inhibition of inappropriate actions or action inopportunities would perfectly complement this putative parietal function [10] — as if reflecting the opposite side of the same coin (compare [14]). It is important to stress that the aforementioned types of prospective action inhibition are not only a theoretical construct. The investigation of human corticospinal excitability has revealed direct physiological signs of prospective
Current Biology 28, R1190–R1211, October 22, 2018 R1201
Current Biology
Dispatches inhibition during action preparation, such as to prevent impulsive responses, to delay the execution of motor plans until the right moment, or to inhibit competing or undesirable behavioral options [15,16]. Posterior parietal cortex, and in particular the negative motor area described by Desmurget et al. [1], may be well suited to mediate such effects [17]. Additional research is needed to critically investigate these ideas and to link them to neuropsychiatric phenomena [18]. For instance, given the aforesaid, it may not be surprising that parietal lesions can cause involuntary limb movements. This is the case in the posterior variant of the alien hand syndrome [19], which well might reflect patients’ inability to inhibit action opportunities [20]. Clearly, the study of Desmurget et al. [1] provides ‘stimulating’ clues that will fuel future investigations about how posterior parietal cortex could support us in realizing an optimal course of action through both the excitation and inhibition of goal-directed movement.
REFERENCES 1. Desmurget, M., Richard, N., Beuriat, P.-A., Szathmari, A., Mottolese, C., Duhamel, J.-R., and Sirigu, A. (2018). Selective inhibition of volitional hand movements after stimulation of the dorsoposterior parietal cortex in humans. Curr. Biol. 28, 3303–3309.
2. Borchers, S., Himmelbach, M., Logothetis, N., and Karnath, H.O. (2011). Direct electrical stimulation of human cortex - the gold standard for mapping brain functions? Nat. Rev. Neurosci. 13, 63–70. 3. Desmurget, M., and Sirigu, A. (2015). Revealing humans’ sensorimotor functions with electrical cortical stimulation. Philos. Trans. R. Soc. Lond. B 370, 20140207. 4. Penfield, W., and Boldrey, E. (1937). Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation. Brain 60, 389–443. 5. Lu¨ders, H.O., Dinner, D.S., Morris, H.H., Wyllie, E., and Comair, Y.G. (1995). Cortical electrical stimulation in humans. The negative motor areas. Adv. Neurol. 67, 115–129. 6. Filevich, E., Ku¨hn, S., and Haggard, P. (2012). Negative motor phenomena in cortical stimulation: implications for inhibitory control of human action. Cortex 48, 1251–1261. 7. Aron, A.R., Robbins, T.W., and Poldrack, R.A. (2014). Inhibition and the right inferior frontal cortex: one decade on. Trends Cogn. Sci. 18, 177–185. 8. Andersen, R.A., and Cui, H. (2009). Intention, action planning, and decision making in parietal-frontal circuits. Neuron 63, 568–583. 9. Culham, J.C., Cavina-Pratesi, C., and Singhal, A. (2006). The role of parietal cortex in visuomotor control: what have we learned from neuroimaging? Neuropsychologia 44, 2668–2684. 10. Lindner, A., Iyer, A., Kagan, I., and Andersen, R.A. (2010). Human posterior parietal cortex plans where to reach and what to avoid. J. Neurosci. 30, 11715–11725.
11. Klaes, C., Westendorff, S., Chakrabarti, S., and Gail, A. (2011). Choosing goals, not rules: deciding among rule-based action plans. Neuron 70, 536–548. 12. Iyer, A., Lindner, A., Kagan, I., and Andersen, R.A. (2010). Motor preparatory activity in posterior parietal cortex is modulated by subjective absolute value. PLoS Biol. 8, e1000444. 13. Cisek, P. (2012). Making decisions through a distributed consensus. Curr. Opin. Neurobiol. 22, 927–936. 14. Mostofsky, S.H., and Simmonds, D.J. (2008). Response inhibition and response selection: two sides of the same coin. J. Cogn. Neurosci. 20, 751–761. 15. Duque, J., Greenhouse, I., Labruna, L., and Ivry, R.B. (2017). Physiological markers of motor inhibition during human behavior. Trends Neurosci. 40, 219–236. 16. Bestmann, S., and Duque, J. (2016). Transcranial magnetic stimulation: decomposing the processes underlying action preparation. Neuroscientist 22, 392–405. 17. Rathelot, J.A., Dum, R.P., and Strick, P.L. (2017). Posterior parietal cortex contains a command apparatus for hand movements. Proc. Natl. Acad. Sci. USA 114, 4255–4260. 18. Aron, A.R. (2011). From reactive to proactive and selective control: developing a richer model for stopping inappropriate responses. Biol. Psychiatry. 69, e55–e68. 19. Hassan, A., and Josephs, K.A. (2016). Alien hand syndrome. Curr. Neurol. Neurosci. Rep. 16, 73. 20. McBride, J., Sumner, P., Jackson, S.R., Bajaj, N., and Husain, M. (2013). Exaggerated object affordance and absent automatic inhibition in alien hand syndrome. Cortex 49, 2040–2054.
Sensory Biology: Structure of an Insect Chemoreceptor Yichen Luo and John R. Carlson* Dept. of Molecular, Cellular and Developmental Biology, Interdepartmental Neuroscience Program, Yale University, New Haven, CT 06520-8103, USA *Correspondence: [email protected] https://doi.org/10.1016/j.cub.2018.09.002
Odorant receptors detect a vast diversity of chemical compounds and underlie many aspects of life. The structure of insect odorant receptors, however, has remained unknown. A cryo-EM study now reveals an intriguing architecture. Twenty years have elapsed since the first insect odorant receptors were identified [1,2]. Odorant receptors may be the
largest family of ion channels in the animal kingdom: an enormous number of insect species have them, each species has
R1202 Current Biology 28, R1190–R1211, October 22, 2018 ª 2018 Elsevier Ltd.
many of them, and their sequences are highly divergent. The odorant receptors detect and discriminate among