576
ethical committee of each district (ie, about seventy in the Thames Regions) will have to be approached. Such a policy would seriously hinder continuation of the study. There is a strong case for establishing regional or even national ethical committees for studies of regional or national scope if there are no issues peculiar to particular districts. The
the basis of HIV the prevalence figures among general population of active women has been criticised. No sexually information on risk factors will be available; many sexually active women intend never to become pregnant; pregnancy terminations will be missed, and these women may well be at higher risk of HIV infection; and with the right to opt out of anonymous testing no scheme can claim to be comprehensive. Emphasis on the right to opt out may well come to be regretted. In the USA, no individual rights are recognised over an anonymised residuum of a blood sample taken for other purposes. With possibilities of testing pools of 10 or even 50 samples simultaneously, and of randomly selecting only some samples for testing (so that no individual would ever know whether or not her sample had been tested), it is difficult to see who benefits from the right to opt out. The degree to which the right is exercised will need careful monitoring. Terminations clearly pose a problem and parallel studies will be required to evaluate the distortion that they induce. That pregnant women do not represent all sexually active women has to be treated in this context as an unfortunate fact of life. There is no other source of material on that scale, and unless evidence of serious bias is forthcoming, the reduction in statistical uncertainty due to the numbers would seem far to outweigh a minor bias due to self-selection. The lack of risk factor information becomes a drawback once prevalence becomes appreciable. Thus, in the results of the latest study, one would like to know where and how the 0-49 per thousand prevalence in inner London arises. In some areas of London it would therefore seem appropriate to conduct named, with consent, testing in parallel with anonymous testing. The former provides risk-factor information, the latter provides lack of bias. The 4 per 100 000 prevalence outside London is a less urgent target for further work. use
of pregnant
women as
Even with all these caveats, the value of Professor Peckham’s results can be clearly seen, and it is not difficult to envisage the increasing value that will accumulate as a time-series of such results becomes available covering the UK. Greatly protracted discussion on the rights and wrongs of anonymous testing has delayed the introduction of a national programme in Britain by several years, to the serious detriment of public health control of the disease. This latest study provides baseline data two years earlier than would otherwise have been the case.
1. Short term prediction of HIV infection and AIDS in England and Wales: report of a working group (the Cox report). London: HM Stationery 2.
3.
4.
Office, 1988. Working group report to Director of Public Health Laboratory Service (the Day report). Acquired immune deficiency syndrome in England and Wales to end 1993—projections using data to end September 1989. Commun Dis Rep Jan 1990 (suppl). Gill ON, Day NE, Adler MW. Monitoring the prevalence of HIV. Br Med J 1989; 299: 1295-98. Carne CA, Weller IVD, Johnson AM, et al. Prevalence of antibodies to human immunodeficiency virus, gonorrhoea rates, and changed sexual
behaviour in homosexual men in London. Lancet 1989; i: 656-58. 5. Evans BA, McLean KA, Dawson SG, et al. Trends in sexual behaviour and risk factors for HIV infection among homosexual men, 1984-7. Br Med J 1989, 298: 215-18. 6. Grant DB, Smith I. Survey of neonatal screening for primary hypothyroidism in England, Wales, and Northern Ireland 1982-4. Br Med J 1988; 296: 1355-58.
MAGNETOENCEPHALOGRAPHY The electrical
activity of the brain produces changes in potential (the electroencephalogram, EEG); in current, detectable by the resulting magnetic fields (the magnetoencephalogram, MEG); and in electrical impedance. The EEG is a long-established method of investigating cerebral function; cerebral impedance imaging is in its infancy, but MEG is undergoing rapid development in many centres worldwide. The brain’s magnetic signals are extremely weak-about 10-13 tesla by comparison with the geomagnetic field of 5 x 10-5 tesla and the typical urban magnetic noise level of 5 x 10-7 tesla / JHz. MEG became feasible only with the development of sensitive superconducting quantum interference devices (SQUIDS) and gradiometers (systems of detector coils that discriminate against distant noise sources). MEG systems have evolved swiftly from cumbersome single-channel probes incapable of sampling the field at more than one location on the head at a time, to arrays of over twenty-five channels, now commercially available at prices of 1-2 million. The scalp EEG is only indirectly related to neuronal generators, since it arises from the volume currents that flow
throughout the brain and its coverings. The poor conductivity of the skull and inhomogeneous impedance of the brain attenuate and distort the spatial pattern of the it is difficult to locate the source. The theoretical advantage of the MEG is that the magnetic fields of the brain are not greatly affected by the medium through which they pass. In an idealised homogeneous spherical head, an elemental current generator produces a simple magnetic field which enters and leaves the head at two points or extrema. The underlying generator lies at the bisector of the line joining the extrema; its direction is perpendicular to this line and its depth is linearly related to the distance between the extrema.1 Departures from the idealised spherical head and variations in internal conductivity may lead to a volume current contribution that could distort the magnetic field. However, many experimental isofield maps obtained from evoked response and epilepsy studies2,3 show that the idealised model usually holds true, so the volume current contamination is small. The difficulty of deducing the underlying current distribution from either magnetic field (MEG) or electrical potential measurements (EEG) exemplifies the wider class of "inverse problems".4 Such problems seldom have a unique mathematical solution, and become insoluble when more than one spatially restricted generator is responsible for the observed patterns. However, given the constraints of anatomy and existing knowledge, it is often possible to decide between mathematically
EEG,
so
577
equivalent descriptions of the data on the grounds of plausibility. MEG performs well in localising focal epileptogenic generators by comparison with other imaging techniques and invasive electrocorticogram measurements.2,S--8 EEG and MEG recordings of the same interictal event often show totally different waveforms, with a variable temporal relation9 that evidently reflects different physiological processes
or
different generators. Modena
et
aP°
reported
single-channel MEG measurements in benign childhood epilepsy in which the MEG revealed abnormal signals that absent from both interictal and ictal EEG records. MEG recordings of evoked responses provide greater topographic resolution than do potential measurements. Thus various components of the somatosensory response to stimulation of nerves in the forearm or leg have different equivalent dipole sources in the corresponding projection areas,11,12 and both ipsilateral and contralateral responses are demonstrable over the second somatosensory area.13 The processing of information relating to different frequencies at different sites within the primary auditory cortex is clearly demonstrable by MEG14 and relates to perceived rather than spectral pitch.15 The amplitude and sources of evoked response components are altered by changes in physical characteristics of the stimuli and are sensitive to minor deviations within an otherwise uniform series of stimuli.16 Simultaneous stimuli in different modalities have complex effects: the responses are not merely the sum of the estimated sources for each modality Y Clinical MEG studies have lately included recordings made during migraine attacks which show changes similar to those produced by spreading depression in laboratory animals-a slow biphasic wave followed by general reduction of activity lasting 10 min.18 EEG and MEG are complementary methods of investigation: sources that are radially oriented do not alter the magnetic field (but are the main source of the EEG) whereas MEG is preferentially sensitive to generators lying in the sulci, which include much of the primary sensory projection areas. Combined EEG and MEG studies therefore offer a good possibility of localising cerebral were
activity. 1. Williamson SL, Kaufman L. Magnetic fields of the cerebral cortex. In: Erne SN, Hahlbohm HD, Lubig H, eds. Biomagnetism. Berlin: Walter de Gruyter, 1981: 353-402. 2. Barth DS, Sutherling W, Broffman J. Neuromagnetic localization of epileptiform spike activity in the human brain. Science 1982; 218: 891-94. 3. Sutherling W, Crandall PH, Darcey TM, Berlin DP, Levesque MF, Barth DS. The magnetic and electric fields agree with intracranial localisation of somatosensory cortex. Neurology (NY) 1988; 38: 1705-13. 4. Sarvas J. Basic mathematical and electromagnetic concepts of the biomagnetic inverse problem. Phys Med Biol 1987; 32: 11-22. 5. Barth DS, Sutherling W, Engel J. Neuromagnetic evidence of spatially distributed sources underlying epileptiform spikes in the human brain. Science 1984; 223: 293-96. 6. Ricci GB, Romani GL, Salustri C, et al. Study of focal epilepsy by multichannel neuromagnetic measurements. Electroencephalogr Clin Neurophysiol 1987; 66: 358-68. 7. Rose DF, Sato S, Smith PD, et al. Localisation of magnetic interictal discharges in temporal lobe epilepsy. Ann Neurol 1987; 22: 348-54. 8. Rose DF, Smith PD, Sato S. Magnetoencephalography and epilepsy research. Science 1987; 238: 319-35. 9. Guy CN, Binnie CD, Cayllesi A, et al. 7th International Conference on Biomagnetism, New York, 1989: 253 (abstr). 10. Modena I, Ricci GB, Barbanera S, Leoni R, Romani GL, Carelli P. Biomagnetic measurements of spontaneous brain activity in epileptic patients. Electroencephalogr Clin Neurophysiol 1982; 54: 622-28.
11. Huttunen J, Hari R, Leinonen L. Cerebral magnetic fields to stimulation of ulnar and median nerves. Electroencephalogr Clin Neurophysiol 1987; 66: 391-400. 12. Huutunen J, Kaukoranta E, Hari R. Cerebral magnetic responses to stimulation of tibial and sural nerves. J Neurol Sci 1987; 79: 43-54. 13. Hari R, Hämäläinen M, Kaukoranta E, Reinikainen K, Tezner D. Neuromagnetic responses from the second sensory cortex in man. Acta Neurol Scand 1983; 68: 207-12. 14. Romani GL, Williamson SJ, Kaufman L. Characterization of the human auditory cortex by the neuromagnetic method. Exp Brain Res 1982; 47: 381-93. 15. Pantev C, Hoke M, Lütkenhöner B. Tonotopic organisation of the auditory cortex revisited: frequency versus pitch representation. In: Williamson SJ, Hoke M, Kotani M, Stroink G, eds. Advances in biomagnetism. New York: Plenum (in press). 16. Hari R. Activation of the human auditory cortex by various sound sequences. In: Williamson SJ, Hoke M. Kotani M, Stroink G, eds. Advances in biomagnetism. New York: Plenum (in press). 17. Weinberg H, Cheyne DO, Brickett P, Harrop R, Gordon R. An interaction of cortical sources associated with simultaneous auditory and somesthetic stimulation. In: Pfurtcheller G, Loopes da Silva FH, eds. Functional brain imaging. Toronto: Hans Huber; 1988: 83-88. 18. Teply N, Barcley GL, Moran J, Simians RT, Welch KMA. Observation of spreading cortical depression in migraine patients. In: Williamson SJ, Hoke M, Kotani M, Stroink G, eds. Advances in biomagnetism. New York: Plenum (in press).
CARING FOR DISABLED PEOPLE’S HEALTH IN BRITAIN In 1984 Gloag1 described UK services for young adults with physical disabilities as the "worst in Europe". Five years later Thomas, Bax, and Smyth,in their study of the health and social needs of adults with physical disabilities, find that little has changed. Health districts up and down the country appear reluctant to consider the long-term needs of people with physical disabilities or those with brain injury. Thomas et al studied 100 physically disabled people aged 18-25 years and uncovered widespread neglect by the generic (mainstream) services. Thus, 40% had not seen a specialist doctor for over 2 years and, although 60% had health problems worthy of attention, only 28% had received regular hospital treatment after leaving school. Those with restricted mobility were not receiving adequate physiotherapy or exercise to maintain their physical abilities, nor were their mobility aids in good working order. The individuals in this sample had very little personal knowledge of their health care needs--eg, a person with spina bifida who was susceptible to accidental damage because of skin anaesthesia did not understand why he got pressure sores. Thomas and colleagues estimate that there are about 22 000 people with physical disabilities in this age group in the UK. Will the 1989 white-papers Working for Patients and Caring for People lead to better health care for disabled people? There is little incentive for general practitioners or health authorities to divert resources to this group, but a strong move to develop generic primary care and neighbourhood nursing teams. The trouble is that generic health care for all is not yet achievable. This philosophy could lead to the dismantling of existing specialist health care teams for people with learning disabilities (mental handicap) rather than the expansion of their remit to include people with other disabilities. Thomas et al found that patients who had both learning and physical disabilities were least well provided for, and suggest that the absence or reduction of medical input in many community mental handicap teams might be the explanation. Powerful specialties are seldom vocal in their support of these less celebrated services, but the Royal College of Physicians made similar recommendations to those of Thomas et al in their 1986 report on physical disability. An important point
ethical committee of each district (ie, about seventy in the Thames Regions) will have to be approached. Such a policy would seriously hinder continuation of the study. There is a strong case for establishing regional or even national ethical committees for studies of regional or national scope if there are no issues peculiar to particular districts. The
the basis of HIV the prevalence figures among general population of active women has been criticised. No sexually information on risk factors will be available; many sexually active women intend never to become pregnant; pregnancy terminations will be missed, and these women may well be at higher risk of HIV infection; and with the right to opt out of anonymous testing no scheme can claim to be comprehensive. Emphasis on the right to opt out may well come to be regretted. In the USA, no individual rights are recognised over an anonymised residuum of a blood sample taken for other purposes. With possibilities of testing pools of 10 or even 50 samples simultaneously, and of randomly selecting only some samples for testing (so that no individual would ever know whether or not her sample had been tested), it is difficult to see who benefits from the right to opt out. The degree to which the right is exercised will need careful monitoring. Terminations clearly pose a problem and parallel studies will be required to evaluate the distortion that they induce. That pregnant women do not represent all sexually active women has to be treated in this context as an unfortunate fact of life. There is no other source of material on that scale, and unless evidence of serious bias is forthcoming, the reduction in statistical uncertainty due to the numbers would seem far to outweigh a minor bias due to self-selection. The lack of risk factor information becomes a drawback once prevalence becomes appreciable. Thus, in the results of the latest study, one would like to know where and how the 0-49 per thousand prevalence in inner London arises. In some areas of London it would therefore seem appropriate to conduct named, with consent, testing in parallel with anonymous testing. The former provides risk-factor information, the latter provides lack of bias. The 4 per 100 000 prevalence outside London is a less urgent target for further work. use
of pregnant
women as
Even with all these caveats, the value of Professor Peckham’s results can be clearly seen, and it is not difficult to envisage the increasing value that will accumulate as a time-series of such results becomes available covering the UK. Greatly protracted discussion on the rights and wrongs of anonymous testing has delayed the introduction of a national programme in Britain by several years, to the serious detriment of public health control of the disease. This latest study provides baseline data two years earlier than would otherwise have been the case.
1. Short term prediction of HIV infection and AIDS in England and Wales: report of a working group (the Cox report). London: HM Stationery 2.
3.
4.
Office, 1988. Working group report to Director of Public Health Laboratory Service (the Day report). Acquired immune deficiency syndrome in England and Wales to end 1993—projections using data to end September 1989. Commun Dis Rep Jan 1990 (suppl). Gill ON, Day NE, Adler MW. Monitoring the prevalence of HIV. Br Med J 1989; 299: 1295-98. Carne CA, Weller IVD, Johnson AM, et al. Prevalence of antibodies to human immunodeficiency virus, gonorrhoea rates, and changed sexual
behaviour in homosexual men in London. Lancet 1989; i: 656-58. 5. Evans BA, McLean KA, Dawson SG, et al. Trends in sexual behaviour and risk factors for HIV infection among homosexual men, 1984-7. Br Med J 1989, 298: 215-18. 6. Grant DB, Smith I. Survey of neonatal screening for primary hypothyroidism in England, Wales, and Northern Ireland 1982-4. Br Med J 1988; 296: 1355-58.
MAGNETOENCEPHALOGRAPHY The electrical
activity of the brain produces changes in potential (the electroencephalogram, EEG); in current, detectable by the resulting magnetic fields (the magnetoencephalogram, MEG); and in electrical impedance. The EEG is a long-established method of investigating cerebral function; cerebral impedance imaging is in its infancy, but MEG is undergoing rapid development in many centres worldwide. The brain’s magnetic signals are extremely weak-about 10-13 tesla by comparison with the geomagnetic field of 5 x 10-5 tesla and the typical urban magnetic noise level of 5 x 10-7 tesla / JHz. MEG became feasible only with the development of sensitive superconducting quantum interference devices (SQUIDS) and gradiometers (systems of detector coils that discriminate against distant noise sources). MEG systems have evolved swiftly from cumbersome single-channel probes incapable of sampling the field at more than one location on the head at a time, to arrays of over twenty-five channels, now commercially available at prices of 1-2 million. The scalp EEG is only indirectly related to neuronal generators, since it arises from the volume currents that flow
throughout the brain and its coverings. The poor conductivity of the skull and inhomogeneous impedance of the brain attenuate and distort the spatial pattern of the it is difficult to locate the source. The theoretical advantage of the MEG is that the magnetic fields of the brain are not greatly affected by the medium through which they pass. In an idealised homogeneous spherical head, an elemental current generator produces a simple magnetic field which enters and leaves the head at two points or extrema. The underlying generator lies at the bisector of the line joining the extrema; its direction is perpendicular to this line and its depth is linearly related to the distance between the extrema.1 Departures from the idealised spherical head and variations in internal conductivity may lead to a volume current contribution that could distort the magnetic field. However, many experimental isofield maps obtained from evoked response and epilepsy studies2,3 show that the idealised model usually holds true, so the volume current contamination is small. The difficulty of deducing the underlying current distribution from either magnetic field (MEG) or electrical potential measurements (EEG) exemplifies the wider class of "inverse problems".4 Such problems seldom have a unique mathematical solution, and become insoluble when more than one spatially restricted generator is responsible for the observed patterns. However, given the constraints of anatomy and existing knowledge, it is often possible to decide between mathematically
EEG,
so
577
equivalent descriptions of the data on the grounds of plausibility. MEG performs well in localising focal epileptogenic generators by comparison with other imaging techniques and invasive electrocorticogram measurements.2,S--8 EEG and MEG recordings of the same interictal event often show totally different waveforms, with a variable temporal relation9 that evidently reflects different physiological processes
or
different generators. Modena
et
aP°
reported
single-channel MEG measurements in benign childhood epilepsy in which the MEG revealed abnormal signals that absent from both interictal and ictal EEG records. MEG recordings of evoked responses provide greater topographic resolution than do potential measurements. Thus various components of the somatosensory response to stimulation of nerves in the forearm or leg have different equivalent dipole sources in the corresponding projection areas,11,12 and both ipsilateral and contralateral responses are demonstrable over the second somatosensory area.13 The processing of information relating to different frequencies at different sites within the primary auditory cortex is clearly demonstrable by MEG14 and relates to perceived rather than spectral pitch.15 The amplitude and sources of evoked response components are altered by changes in physical characteristics of the stimuli and are sensitive to minor deviations within an otherwise uniform series of stimuli.16 Simultaneous stimuli in different modalities have complex effects: the responses are not merely the sum of the estimated sources for each modality Y Clinical MEG studies have lately included recordings made during migraine attacks which show changes similar to those produced by spreading depression in laboratory animals-a slow biphasic wave followed by general reduction of activity lasting 10 min.18 EEG and MEG are complementary methods of investigation: sources that are radially oriented do not alter the magnetic field (but are the main source of the EEG) whereas MEG is preferentially sensitive to generators lying in the sulci, which include much of the primary sensory projection areas. Combined EEG and MEG studies therefore offer a good possibility of localising cerebral were
activity. 1. Williamson SL, Kaufman L. Magnetic fields of the cerebral cortex. In: Erne SN, Hahlbohm HD, Lubig H, eds. Biomagnetism. Berlin: Walter de Gruyter, 1981: 353-402. 2. Barth DS, Sutherling W, Broffman J. Neuromagnetic localization of epileptiform spike activity in the human brain. Science 1982; 218: 891-94. 3. Sutherling W, Crandall PH, Darcey TM, Berlin DP, Levesque MF, Barth DS. The magnetic and electric fields agree with intracranial localisation of somatosensory cortex. Neurology (NY) 1988; 38: 1705-13. 4. Sarvas J. Basic mathematical and electromagnetic concepts of the biomagnetic inverse problem. Phys Med Biol 1987; 32: 11-22. 5. Barth DS, Sutherling W, Engel J. Neuromagnetic evidence of spatially distributed sources underlying epileptiform spikes in the human brain. Science 1984; 223: 293-96. 6. Ricci GB, Romani GL, Salustri C, et al. Study of focal epilepsy by multichannel neuromagnetic measurements. Electroencephalogr Clin Neurophysiol 1987; 66: 358-68. 7. Rose DF, Sato S, Smith PD, et al. Localisation of magnetic interictal discharges in temporal lobe epilepsy. Ann Neurol 1987; 22: 348-54. 8. Rose DF, Smith PD, Sato S. Magnetoencephalography and epilepsy research. Science 1987; 238: 319-35. 9. Guy CN, Binnie CD, Cayllesi A, et al. 7th International Conference on Biomagnetism, New York, 1989: 253 (abstr). 10. Modena I, Ricci GB, Barbanera S, Leoni R, Romani GL, Carelli P. Biomagnetic measurements of spontaneous brain activity in epileptic patients. Electroencephalogr Clin Neurophysiol 1982; 54: 622-28.
11. Huttunen J, Hari R, Leinonen L. Cerebral magnetic fields to stimulation of ulnar and median nerves. Electroencephalogr Clin Neurophysiol 1987; 66: 391-400. 12. Huutunen J, Kaukoranta E, Hari R. Cerebral magnetic responses to stimulation of tibial and sural nerves. J Neurol Sci 1987; 79: 43-54. 13. Hari R, Hämäläinen M, Kaukoranta E, Reinikainen K, Tezner D. Neuromagnetic responses from the second sensory cortex in man. Acta Neurol Scand 1983; 68: 207-12. 14. Romani GL, Williamson SJ, Kaufman L. Characterization of the human auditory cortex by the neuromagnetic method. Exp Brain Res 1982; 47: 381-93. 15. Pantev C, Hoke M, Lütkenhöner B. Tonotopic organisation of the auditory cortex revisited: frequency versus pitch representation. In: Williamson SJ, Hoke M, Kotani M, Stroink G, eds. Advances in biomagnetism. New York: Plenum (in press). 16. Hari R. Activation of the human auditory cortex by various sound sequences. In: Williamson SJ, Hoke M. Kotani M, Stroink G, eds. Advances in biomagnetism. New York: Plenum (in press). 17. Weinberg H, Cheyne DO, Brickett P, Harrop R, Gordon R. An interaction of cortical sources associated with simultaneous auditory and somesthetic stimulation. In: Pfurtcheller G, Loopes da Silva FH, eds. Functional brain imaging. Toronto: Hans Huber; 1988: 83-88. 18. Teply N, Barcley GL, Moran J, Simians RT, Welch KMA. Observation of spreading cortical depression in migraine patients. In: Williamson SJ, Hoke M, Kotani M, Stroink G, eds. Advances in biomagnetism. New York: Plenum (in press).
CARING FOR DISABLED PEOPLE’S HEALTH IN BRITAIN In 1984 Gloag1 described UK services for young adults with physical disabilities as the "worst in Europe". Five years later Thomas, Bax, and Smyth,in their study of the health and social needs of adults with physical disabilities, find that little has changed. Health districts up and down the country appear reluctant to consider the long-term needs of people with physical disabilities or those with brain injury. Thomas et al studied 100 physically disabled people aged 18-25 years and uncovered widespread neglect by the generic (mainstream) services. Thus, 40% had not seen a specialist doctor for over 2 years and, although 60% had health problems worthy of attention, only 28% had received regular hospital treatment after leaving school. Those with restricted mobility were not receiving adequate physiotherapy or exercise to maintain their physical abilities, nor were their mobility aids in good working order. The individuals in this sample had very little personal knowledge of their health care needs--eg, a person with spina bifida who was susceptible to accidental damage because of skin anaesthesia did not understand why he got pressure sores. Thomas and colleagues estimate that there are about 22 000 people with physical disabilities in this age group in the UK. Will the 1989 white-papers Working for Patients and Caring for People lead to better health care for disabled people? There is little incentive for general practitioners or health authorities to divert resources to this group, but a strong move to develop generic primary care and neighbourhood nursing teams. The trouble is that generic health care for all is not yet achievable. This philosophy could lead to the dismantling of existing specialist health care teams for people with learning disabilities (mental handicap) rather than the expansion of their remit to include people with other disabilities. Thomas et al found that patients who had both learning and physical disabilities were least well provided for, and suggest that the absence or reduction of medical input in many community mental handicap teams might be the explanation. Powerful specialties are seldom vocal in their support of these less celebrated services, but the Royal College of Physicians made similar recommendations to those of Thomas et al in their 1986 report on physical disability. An important point
