SCIENCE TIMES
Figure. MLR stimulation improves swimming in animals with subtotal spinal cord injuries (,10% remaining white matter). A-E, individual animals with sever, 91% to 97.5% lesions of the T10 spinal cord are color-coded according to the amount of spared white matter from blue (least spared) to red (most spared). F, estimation of remaining fibers of the major descending tracts from the brain in these animals. G, walking speed without stimulation was fully compensated by the forelimbs and increased with increasing MLR DBS intensity. H, occasional, nonfunctional step-like twitches were scarce, illustrating the sever hindlimb deficits. Despite a slight increase of stepping frequency, no functional steps with MLR DBS were seen. I, under weight-released conditions, swimming speed increased with increasing stimulation intensity. J, Hindlimb stroke frequency increased slightly with stimulation. K and L, representative joint trajectories of the swimming animal show in (D) without MLR DBS (K) and with 100% MLR DBS (L). Joint trajectories are shown at 20-ms intervals. X axis, intensity of MLR BDS as a percent of maximal stimulation (123 6 47.1 mA). *P , .05, **P , .01, ***P , .001, 1-way ANOVA with Dunnett’s multiple comparison to 0% stimulation. Dashed horizontal line indicates the mean intact baseline performance. (From [Bachmann LC, Matis A, Lindau NT, Felder P, Gullo M, Schwab ME. Deep Brain Stimulation of the Midbrain Locomotor Region Improves Paretic Hindlimb Function After Spinal Cord Injury in Rats. Sci Transl Med. 2013;23;5(208):208ra146]. Reprinted with permission from AAAS).
Traumatic Brain Injury at Your Fingertips!
A
rguably the greatest functional feature of today’s most popular portable/handheld smart devices is specific application software. There is a cornucopia of “apps” to aid for any task available for download at finger length. There are more than 900 000 iPhone apps currently available, and the number of smart phone app downloads is expected to increase to 40 billion in 2014 alone.1,2 The significance of these apps lies in their functionality:
NEUROSURGERY
they serve as interactive tools that, if designed appropriately, can play effective roles in assessing or reviewing information at a moment’s notice to help one make the best possible judgment in almost any situation. Unbeknownst to most neurosurgeons and the public, neurosurgery is no exception. As of September 10, 2013, there are more than 50 neurosurgery related apps in the iTunes store. Currently, there are more than 20 apps related to traumatic brain injury (TBI) (Table 1) for the iPhone. In addition to serving as educational resources, these apps contain a range of medical assessments including various algorithms, scales,
and calculators for use by health care professionals and caretakers alike. There are also apps that attempt to provide lifestyle modifications for patients with communication ailments. Although there are several TBI-related apps in the market, a few may be considered particularly useful for neurosurgeons or as a recommendation for use by patients, and this paper is a brief review of some of these useful apps. Traumatic Brain Injury (by Fuze.cc) (Figure A): This is an educational app developed by physicians and neurosurgeons in Brazil designed to serve as an aid to learn or review the general topics in TBI. Currently, it appears to be the most
VOLUME 74 | NUMBER 2 | FEBRUARY 2014 | N19
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
SCIENCE TIMES
Figure. Screen shots of various apps related to TBI. A, Traumatic Brain Injury app showing an example of intracranial hematomas. B, mTBI Pocket Guide app with various categories of information. C, Concussion app, and D, Return2Play for concussion app showing an example of calendar for symptoms.
comprehensive review of TBI of all the apps on iTunes. The app contains schematic figures, pictures of real cases, scales related to TBI, in addition to the diagnosis, management, and
N20 | VOLUME 74 | NUMBER 2 | FEBRUARY 2014
treatment of various conditions under the umbrella of TBI. Samples of topics reviewed are TBI physiology, subdural/epidural hematoma, diffuse axonal injury (DAI), decompressive
craniectomy, ventricular drain management, and various aspects of intensive care. mTBI Pocket Guide (by The National Center for Telehealth and Technology) (Figure B) is also
www.neurosurgery-online.com
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
SCIENCE TIMES
Table. Some of the iPhone Apps Related to Traumatic Brain Injury (TBI) Name
Category
Tool Type
Audience
Stars
Price ($)
mTBI Pocket guide Traumatic Brain Injury
Medical Medical
Teaching Teaching
Medical providers Medical providers
3.5 4
Free 4.99
SCAT2 app SCAT2- Sport Concussion Glasgow Pro Concussion
Medical Medical Medical Medical
Calculator Calculator Calculator Evaluation
Professional and general Professional and general General General
N/A 4 N/A 4
3.99 Free Free Free
Communication Productivity Medical Medical Medical Game Education Education Medical Medical Communication Communication Medical
Speech Organizer Evaluation Neurologist Locator Speech Word Recognition Teaching Organizer Calculator Calculator Organizer Evaluation Tracker/Sensor
General General General General Patients Patients General General General General General Patients General
N/A N/A 4 N/A N/A 4 N/A N/a N/A N/A N/A NA N/A
59.99 Free Free Free Free Free Free 39.99 Free Free 4.99 Free Free
For medical providers
For general providers
For patients Voice 4u AAC Communication CanPlan Concussion Concussion Check Grid Player Guess My Word! Heads Up App Marti Play It Safe Concussion. . . Pocket SCAT2 Qcard Return2Play Shockbox
a very comprehensive app designed for use by providers who evaluate and treat patients with mild TBI and includes guidelines on TBI management, patient education tools, and TBI assessment and questionnaires. It can also help physicians with ICD-9 coding and provides links to various other TBI-related resources that can be very useful to those taking care of TBI patients. And the app is free! TBI Resource (by Patrick Mosa, Eastern Washington University) is an information and educational tool for families and caregivers of patients with TBI. There are several apps that are related to concussion. Concussion (by SportSafety Labs, LLC (Figure C) is one such useful app that provides educational tools for parents, coaches, and health care providers to diagnose concussion and post concussion symptoms. It can be useful at sporting events and includes functions such as call an ambulance via 911, locate the nearest hospital with driving directions, and send your location coordinates to emergency contact and rescue personnel. SCAT2, Pocket SCAT, and SCAT 2 app: The Sport Concussion Assessment Tool 2 (SCAT2) was developed by a group of international experts at the 3rd International Consensus meeting in 2008 with the objective to standardize the method for evaluating injured athletes (.10 years age) who suffered a concussion. The app assesses concussion status by using various scales and surveys to assess pain, motor abilities, and sensation. This
NEUROSURGERY
allows for calculation of the Standardized Assessment of Concussion (SAC) score and Maddocks questions for sideline concussion assessment. The Pocket SCAT2 is a shorter version of the SCAT2 for use by coaches and parents to assess concussion. Additionally, the “SCAT2 app” can save assessments which can be emailed to medical professionals. These apps may be more useful for other healthcare professionals, coaches, or parents to help gather data of the traumatic situation at hand as it relates to TBI. The use of these types of apps by caretakers may help to more effectively translate the information to medical services during the crucial time of injury, which may possibly result in faster response times of appropriate medical specialties and greater recovery outcomes. Return2Play for concussion (by the Pediatric Trauma program at C.S. Mott Children’s Hospital and University of Michigan) (Figure D) is a concussion recovery app that helps patients track their activities and symptoms after a concussion and share this information with their health care providers. Voice4u AAC Communication, Marti, and CanPlan: Many patients who suffer from TBI or other neurological ailments are unable to communicate effectively. These apps lend as simple tools to help facilitate not only the interaction between patients and physicians, but also between patients and others. For example, CanPlan and Marti are similar apps that allow
users to make instructions for custom daily functional processes through the use of video and pictures for things such as making a cup of coffee or showing which medications to take. These videos can be made by physicians or caretakers to serves as guides for patients to be able to replicate any text required. Voice4u is a communication app that allows users to compile, select, or create phrases to show what they are talking about. This way, apps can potentially help patients by improving their ability to complete activities of daily living (ADL) and live more independently. Several associations and help groups have apps specifically designed to help people connect with them. Head injury association app (by Local media solutions) is one such app that aims to maximize TBI survivors’ potential by providing support programs. The appearance of neurosurgery related apps demonstrates a positive trend for the field. For many specialties in medicine, there have been remarkable apps that have been designed to aid physicians of all fields (ie, Epocrates). Even within neurosurgery, there exists several popular apps used by many neurosurgeons/residents/ students and midlevel practitioners. NeuroMind (free, by Pieter Kubben, digitalneurosurgeon. com) is one such popular app that covers a broad list of topics including head trauma, scoring systems, and neurosurgical images. Neurosurgery survival guide ($7.99, Dr Neil Roundy) is another such app for quick reference
VOLUME 74 | NUMBER 2 | FEBRUARY 2014 | N21
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
SCIENCE TIMES
on a broad range of neurosurgical topics. Recently, a useful reference list for apps was published in Congress Quarterly by Khan NR et al.3 However, as noted from our search, there is a paucity of true TBI-related apps. An allencompassing app that describes management and treatment of various TBI pathologies with evidence-based neurosurgical literature would be beneficial to neurosurgical students and residents. Such an app would include a review of TBI-related topics and neuroanatomy with sources, various examples of imaging with descriptions, brief guidelines for management, description of pertinent operative procedures, and a directory of searchable drugs with information on how to use them. We believe medical apps can play a significant role by helping to organize data. There is no doubt that patient care can be improved if new smart phone technologies are responsibly and carefully designed. NAUMAN S. CHAUDHRY FAIZ U. AHMAD M. ROSS BULLOCK MICHAEL Y. WANG
REFERENCES 1. Available at: http://www.apple.com/pr/library/2013/01/ 07App-Store-Tops-40-Billion-Downloads-with-AlmostHalf-in-2012.html. 2. Available at: http://mobithinking.com/mobile-marketingtools/latest-mobile-stats/e. 3. Khan NR, Auschwltz T, Choudhri AF, Kllmo P. Iphone resources in neurosurgery. CNS Q Fall. 2013;22-23;. Available at: http://www.cns.org/publications/cnsq/pdf/ CNSQ_13fall.pdf.
Intrinsic Cortical Signal Gain: Optogenetic Silencing Reveals Active Role of Cortical Amplification During Sensory Input
T
he role of the cortex in receiving incoming sensory information provided by thalamic inputs is not completely understood. Is the cortex act a passive receiving system, performing subsequent manipulations on a similar copy of the incoming data, or does it actively transform thalamic input to improve performance or detection? In a recent study, Li et al (Intracortical multiplication of thalamocortical signals in mouse auditory cortex. Nat Neurosci. 2013;16 (9):1179-1181) used an optogenetics technique to support the latter interpretation. The authors dampened intracortical circuitry by activating parvalbumin (PV1) expressing inhibitory neurons locally, and found that in the uninhibited state, primary auditory cortex amplifies thalamocortical responses while leaving the spectral tuning curves preserved. This process appears to increase the duration and gain of thalamic input signals and serves to improve the signal-tonoise properties of the transmitted information. The authors performed this study in anesthetized mice, examining specifically primary auditory cortex (A1). Using blue LED illumination, they
activated the PV1 inhibitory cellular component which had been modified (Cre-loxP recombination using an adeno-associated viral vector) to express channelrhodopsin-2 (ChR2). The PV1 neurons increased their firing rates considerably with illumination. Extracellular multi-unit recordings were performed in A1 for tonotopic mapping, with tone inputs applied to the contralateral ear. Similar recordings were also performed stereotactically in the ventral medial geniculate body (MGBv) in a tonotopic fashion, and loose-patch and whole-cell voltage clamp recordings were made from the Layer IV region of A1 (predominantly pyramidal cells). During optogenetic silencing, the authors found that the cortical response produced by equivalent thalamic inputs (for the same frequency tone stimulus) was reduced by a factor of 2.4 as compared to the normal non-silenced state. Additionally, the time duration of the cortical response was reduced during optogenetic silencing. The response amplification produced by the surrounding cortical input appeared additionally to preserve the preferred cortical response to upward going frequency-modulated sweeps, but the overall amplitude change brought on by optogenetic silencing was independent of direction of frequency sweeps. The onset latencies to sweep inputs remained unchanged between the silenced and non-silenced state, implying that the spectral range of the cortical response is determined by the thalamocortical input component, and not modulated by surrounding cortical input. In summary, Li et al describe an optogenetic method for silencing surrounding cortical influences
Figure. A and C, 2 neurons exhibiting frequency Sdependent tone evoked responses, both during the case of optogenetic silencing of the cortical network (lower traces) and during the non-silenced case (upper traces). B and D, linear nature of pink amplitude of thalamic input vs the total excitation evoked by the same tone stimulus (left subplot). Onset latencies of the thalamocortical (blue) and total cortical (red) excitatory responses at different frequencies (right subplot). (Reprinted by permission from Macmillan Publishers Ltd: Li LY, Li YT, Zhou M, Tao HW, Zhang LI. Intracortical multiplication of thalamocortical signals in mouse auditory cortex. Nat Neurosci. 2013;16 (9):1179-1181).
N22 | VOLUME 74 | NUMBER 2 | FEBRUARY 2014
www.neurosurgery-online.com
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
Figure. MLR stimulation improves swimming in animals with subtotal spinal cord injuries (,10% remaining white matter). A-E, individual animals with sever, 91% to 97.5% lesions of the T10 spinal cord are color-coded according to the amount of spared white matter from blue (least spared) to red (most spared). F, estimation of remaining fibers of the major descending tracts from the brain in these animals. G, walking speed without stimulation was fully compensated by the forelimbs and increased with increasing MLR DBS intensity. H, occasional, nonfunctional step-like twitches were scarce, illustrating the sever hindlimb deficits. Despite a slight increase of stepping frequency, no functional steps with MLR DBS were seen. I, under weight-released conditions, swimming speed increased with increasing stimulation intensity. J, Hindlimb stroke frequency increased slightly with stimulation. K and L, representative joint trajectories of the swimming animal show in (D) without MLR DBS (K) and with 100% MLR DBS (L). Joint trajectories are shown at 20-ms intervals. X axis, intensity of MLR BDS as a percent of maximal stimulation (123 6 47.1 mA). *P , .05, **P , .01, ***P , .001, 1-way ANOVA with Dunnett’s multiple comparison to 0% stimulation. Dashed horizontal line indicates the mean intact baseline performance. (From [Bachmann LC, Matis A, Lindau NT, Felder P, Gullo M, Schwab ME. Deep Brain Stimulation of the Midbrain Locomotor Region Improves Paretic Hindlimb Function After Spinal Cord Injury in Rats. Sci Transl Med. 2013;23;5(208):208ra146]. Reprinted with permission from AAAS).
Traumatic Brain Injury at Your Fingertips!
A
rguably the greatest functional feature of today’s most popular portable/handheld smart devices is specific application software. There is a cornucopia of “apps” to aid for any task available for download at finger length. There are more than 900 000 iPhone apps currently available, and the number of smart phone app downloads is expected to increase to 40 billion in 2014 alone.1,2 The significance of these apps lies in their functionality:
NEUROSURGERY
they serve as interactive tools that, if designed appropriately, can play effective roles in assessing or reviewing information at a moment’s notice to help one make the best possible judgment in almost any situation. Unbeknownst to most neurosurgeons and the public, neurosurgery is no exception. As of September 10, 2013, there are more than 50 neurosurgery related apps in the iTunes store. Currently, there are more than 20 apps related to traumatic brain injury (TBI) (Table 1) for the iPhone. In addition to serving as educational resources, these apps contain a range of medical assessments including various algorithms, scales,
and calculators for use by health care professionals and caretakers alike. There are also apps that attempt to provide lifestyle modifications for patients with communication ailments. Although there are several TBI-related apps in the market, a few may be considered particularly useful for neurosurgeons or as a recommendation for use by patients, and this paper is a brief review of some of these useful apps. Traumatic Brain Injury (by Fuze.cc) (Figure A): This is an educational app developed by physicians and neurosurgeons in Brazil designed to serve as an aid to learn or review the general topics in TBI. Currently, it appears to be the most
VOLUME 74 | NUMBER 2 | FEBRUARY 2014 | N19
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
SCIENCE TIMES
Figure. Screen shots of various apps related to TBI. A, Traumatic Brain Injury app showing an example of intracranial hematomas. B, mTBI Pocket Guide app with various categories of information. C, Concussion app, and D, Return2Play for concussion app showing an example of calendar for symptoms.
comprehensive review of TBI of all the apps on iTunes. The app contains schematic figures, pictures of real cases, scales related to TBI, in addition to the diagnosis, management, and
N20 | VOLUME 74 | NUMBER 2 | FEBRUARY 2014
treatment of various conditions under the umbrella of TBI. Samples of topics reviewed are TBI physiology, subdural/epidural hematoma, diffuse axonal injury (DAI), decompressive
craniectomy, ventricular drain management, and various aspects of intensive care. mTBI Pocket Guide (by The National Center for Telehealth and Technology) (Figure B) is also
www.neurosurgery-online.com
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
SCIENCE TIMES
Table. Some of the iPhone Apps Related to Traumatic Brain Injury (TBI) Name
Category
Tool Type
Audience
Stars
Price ($)
mTBI Pocket guide Traumatic Brain Injury
Medical Medical
Teaching Teaching
Medical providers Medical providers
3.5 4
Free 4.99
SCAT2 app SCAT2- Sport Concussion Glasgow Pro Concussion
Medical Medical Medical Medical
Calculator Calculator Calculator Evaluation
Professional and general Professional and general General General
N/A 4 N/A 4
3.99 Free Free Free
Communication Productivity Medical Medical Medical Game Education Education Medical Medical Communication Communication Medical
Speech Organizer Evaluation Neurologist Locator Speech Word Recognition Teaching Organizer Calculator Calculator Organizer Evaluation Tracker/Sensor
General General General General Patients Patients General General General General General Patients General
N/A N/A 4 N/A N/A 4 N/A N/a N/A N/A N/A NA N/A
59.99 Free Free Free Free Free Free 39.99 Free Free 4.99 Free Free
For medical providers
For general providers
For patients Voice 4u AAC Communication CanPlan Concussion Concussion Check Grid Player Guess My Word! Heads Up App Marti Play It Safe Concussion. . . Pocket SCAT2 Qcard Return2Play Shockbox
a very comprehensive app designed for use by providers who evaluate and treat patients with mild TBI and includes guidelines on TBI management, patient education tools, and TBI assessment and questionnaires. It can also help physicians with ICD-9 coding and provides links to various other TBI-related resources that can be very useful to those taking care of TBI patients. And the app is free! TBI Resource (by Patrick Mosa, Eastern Washington University) is an information and educational tool for families and caregivers of patients with TBI. There are several apps that are related to concussion. Concussion (by SportSafety Labs, LLC (Figure C) is one such useful app that provides educational tools for parents, coaches, and health care providers to diagnose concussion and post concussion symptoms. It can be useful at sporting events and includes functions such as call an ambulance via 911, locate the nearest hospital with driving directions, and send your location coordinates to emergency contact and rescue personnel. SCAT2, Pocket SCAT, and SCAT 2 app: The Sport Concussion Assessment Tool 2 (SCAT2) was developed by a group of international experts at the 3rd International Consensus meeting in 2008 with the objective to standardize the method for evaluating injured athletes (.10 years age) who suffered a concussion. The app assesses concussion status by using various scales and surveys to assess pain, motor abilities, and sensation. This
NEUROSURGERY
allows for calculation of the Standardized Assessment of Concussion (SAC) score and Maddocks questions for sideline concussion assessment. The Pocket SCAT2 is a shorter version of the SCAT2 for use by coaches and parents to assess concussion. Additionally, the “SCAT2 app” can save assessments which can be emailed to medical professionals. These apps may be more useful for other healthcare professionals, coaches, or parents to help gather data of the traumatic situation at hand as it relates to TBI. The use of these types of apps by caretakers may help to more effectively translate the information to medical services during the crucial time of injury, which may possibly result in faster response times of appropriate medical specialties and greater recovery outcomes. Return2Play for concussion (by the Pediatric Trauma program at C.S. Mott Children’s Hospital and University of Michigan) (Figure D) is a concussion recovery app that helps patients track their activities and symptoms after a concussion and share this information with their health care providers. Voice4u AAC Communication, Marti, and CanPlan: Many patients who suffer from TBI or other neurological ailments are unable to communicate effectively. These apps lend as simple tools to help facilitate not only the interaction between patients and physicians, but also between patients and others. For example, CanPlan and Marti are similar apps that allow
users to make instructions for custom daily functional processes through the use of video and pictures for things such as making a cup of coffee or showing which medications to take. These videos can be made by physicians or caretakers to serves as guides for patients to be able to replicate any text required. Voice4u is a communication app that allows users to compile, select, or create phrases to show what they are talking about. This way, apps can potentially help patients by improving their ability to complete activities of daily living (ADL) and live more independently. Several associations and help groups have apps specifically designed to help people connect with them. Head injury association app (by Local media solutions) is one such app that aims to maximize TBI survivors’ potential by providing support programs. The appearance of neurosurgery related apps demonstrates a positive trend for the field. For many specialties in medicine, there have been remarkable apps that have been designed to aid physicians of all fields (ie, Epocrates). Even within neurosurgery, there exists several popular apps used by many neurosurgeons/residents/ students and midlevel practitioners. NeuroMind (free, by Pieter Kubben, digitalneurosurgeon. com) is one such popular app that covers a broad list of topics including head trauma, scoring systems, and neurosurgical images. Neurosurgery survival guide ($7.99, Dr Neil Roundy) is another such app for quick reference
VOLUME 74 | NUMBER 2 | FEBRUARY 2014 | N21
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
SCIENCE TIMES
on a broad range of neurosurgical topics. Recently, a useful reference list for apps was published in Congress Quarterly by Khan NR et al.3 However, as noted from our search, there is a paucity of true TBI-related apps. An allencompassing app that describes management and treatment of various TBI pathologies with evidence-based neurosurgical literature would be beneficial to neurosurgical students and residents. Such an app would include a review of TBI-related topics and neuroanatomy with sources, various examples of imaging with descriptions, brief guidelines for management, description of pertinent operative procedures, and a directory of searchable drugs with information on how to use them. We believe medical apps can play a significant role by helping to organize data. There is no doubt that patient care can be improved if new smart phone technologies are responsibly and carefully designed. NAUMAN S. CHAUDHRY FAIZ U. AHMAD M. ROSS BULLOCK MICHAEL Y. WANG
REFERENCES 1. Available at: http://www.apple.com/pr/library/2013/01/ 07App-Store-Tops-40-Billion-Downloads-with-AlmostHalf-in-2012.html. 2. Available at: http://mobithinking.com/mobile-marketingtools/latest-mobile-stats/e. 3. Khan NR, Auschwltz T, Choudhri AF, Kllmo P. Iphone resources in neurosurgery. CNS Q Fall. 2013;22-23;. Available at: http://www.cns.org/publications/cnsq/pdf/ CNSQ_13fall.pdf.
Intrinsic Cortical Signal Gain: Optogenetic Silencing Reveals Active Role of Cortical Amplification During Sensory Input
T
he role of the cortex in receiving incoming sensory information provided by thalamic inputs is not completely understood. Is the cortex act a passive receiving system, performing subsequent manipulations on a similar copy of the incoming data, or does it actively transform thalamic input to improve performance or detection? In a recent study, Li et al (Intracortical multiplication of thalamocortical signals in mouse auditory cortex. Nat Neurosci. 2013;16 (9):1179-1181) used an optogenetics technique to support the latter interpretation. The authors dampened intracortical circuitry by activating parvalbumin (PV1) expressing inhibitory neurons locally, and found that in the uninhibited state, primary auditory cortex amplifies thalamocortical responses while leaving the spectral tuning curves preserved. This process appears to increase the duration and gain of thalamic input signals and serves to improve the signal-tonoise properties of the transmitted information. The authors performed this study in anesthetized mice, examining specifically primary auditory cortex (A1). Using blue LED illumination, they
activated the PV1 inhibitory cellular component which had been modified (Cre-loxP recombination using an adeno-associated viral vector) to express channelrhodopsin-2 (ChR2). The PV1 neurons increased their firing rates considerably with illumination. Extracellular multi-unit recordings were performed in A1 for tonotopic mapping, with tone inputs applied to the contralateral ear. Similar recordings were also performed stereotactically in the ventral medial geniculate body (MGBv) in a tonotopic fashion, and loose-patch and whole-cell voltage clamp recordings were made from the Layer IV region of A1 (predominantly pyramidal cells). During optogenetic silencing, the authors found that the cortical response produced by equivalent thalamic inputs (for the same frequency tone stimulus) was reduced by a factor of 2.4 as compared to the normal non-silenced state. Additionally, the time duration of the cortical response was reduced during optogenetic silencing. The response amplification produced by the surrounding cortical input appeared additionally to preserve the preferred cortical response to upward going frequency-modulated sweeps, but the overall amplitude change brought on by optogenetic silencing was independent of direction of frequency sweeps. The onset latencies to sweep inputs remained unchanged between the silenced and non-silenced state, implying that the spectral range of the cortical response is determined by the thalamocortical input component, and not modulated by surrounding cortical input. In summary, Li et al describe an optogenetic method for silencing surrounding cortical influences
Figure. A and C, 2 neurons exhibiting frequency Sdependent tone evoked responses, both during the case of optogenetic silencing of the cortical network (lower traces) and during the non-silenced case (upper traces). B and D, linear nature of pink amplitude of thalamic input vs the total excitation evoked by the same tone stimulus (left subplot). Onset latencies of the thalamocortical (blue) and total cortical (red) excitatory responses at different frequencies (right subplot). (Reprinted by permission from Macmillan Publishers Ltd: Li LY, Li YT, Zhou M, Tao HW, Zhang LI. Intracortical multiplication of thalamocortical signals in mouse auditory cortex. Nat Neurosci. 2013;16 (9):1179-1181).
N22 | VOLUME 74 | NUMBER 2 | FEBRUARY 2014
www.neurosurgery-online.com
Copyright © Congress of Neurological Surgeons. Unauthorized reproduction of this article is prohibited.
