Comments on News and Primary Papers
Comment by: Deanna M. Barch
Submitted 13 July 2010
Posted 13 July 2010
Mechanisms of Capacity Limitations in Working Memory
Gold and colleagues have provided an extremely elegant example of how a precisely controlled behavioral study can be used to directly test implications generated by neurobiological theories of cognitive impairment in schizophrenia. Further, they have provided novel and important data in schizophrenia that should cause us to re-examine theories about the mechanisms underling working memory impairments in this illness.
As noted by Gold, it has been hypothesized that altered GABAergic, glutamatergic, and/or dopaminergic inputs into reverberating and oscillatory networks in prefrontal or parietal cortex among individuals with schizophrenia should render such networks unstable and lead to less precise working memory representations that are particularly prone to decay (Lisman et al., 2008; Durstewitz and Seamans, 2008; Rolls et al., 2008; Lewis et al., 2008). However, Gold and colleagues have shown that working memory representations in schizophrenia (at least of color memory) are neither less precise nor show evidence of exceptionally rapid decay. Instead, individuals with schizophrenia showed clearly reduced working memory capacity.
These data contribute to a systemic body of work generated by Gold and colleagues, who have investigated the many aspects of working memory that could be impaired in schizophrenia. They have also shown that iconic decay is not increased in schizophrenia (Hahn et al., 2010), that feature binding is intact (Gold et al., 2003), and that certain aspects of attentional control over working memory are intact (Gold et al., 2006), though others are impaired (Fuller et al., 2006). However, working memory capacity has consistently been shown to be reduced in schizophrenia across numerous studies (Gold et al., 2006; van Raalten et al., 2008; Silver et al., 2003). If we take these results seriously (and we should), they require us to look closely at the neural mechanisms postulated to modulate capacity limitations in working memory in order to generate clues to the mechanisms that may be leading to reduced working memory capacity in schizophrenia.
The neural mechanisms leading to working memory capacity limitations are still very much an open source of debate. However, one influential theory is that the number of “items” that can be maintained in working memory is limited by the number of gamma cycles (30-100 Hz) that can be embedded within a theta cycle (Lisman, 2010). Related to the idea that originally drove the design of the Gold study, Lisman and others have hypothesized that individual items within working memory are represented by oscillating neural populations with spike rates phase-locked in a gamma cycle. The oscillatory activity representing different items must be kept isolated, potentially by keeping gamma activity for different items out of phase with each other. One way to accomplish this would be to couple such gamma cycles into a lower frequency theta oscillation that can help regulate and separate activity associated with different items (as well as maintain information about order). Lisman and others have argued that capacity constraints of approximately four items in working memory (Cowan, 2001) thus reflect the number of gamma cycles that can be embedded in a theta cycle (approximately four) (Lisman, 2010; Wolters and Raffone, 2008).
Gold’s results suggest that it may not be the maintenance of the individual gamma-oscillating neural populations representing individual items that is impaired in schizophrenia. Instead, it may be either the ability to establish such synchronous neural activity associated with a specific item, or the ability to couple a number of different gamma-oscillating sub-networks into a theta cycle. Interestingly, a growing number of studies have shown altered gamma activity during working memory in schizophrenia (Barr et al., 2010; Basar-Eroglu et al., 2007; Light et al., 2006; Kissler et al., 2000), as well as some evidence for altered theta activity (Haenschel et al., 2009). However, additional work is needed to specifically examine gamma-theta coupling in schizophrenia and its role in determining capacity limitations in this disease.
The type of network models of working memory put forth by Wang and colleagues suggest that the dynamics of excitatory and inhibitory inputs drive the number of independent “activity bumps” (i.e., items) that can be maintained in a network (Compte et al., 2000). A related idea about the mechanisms driving capacity limitations and variations in these limits across individuals has been put forth by Klingberg and colleagues, who have argued that the dynamics of such lateral inhibitory mechanisms in parietal cortex limit memory capacity to be between two and seven items (Edin et al., 2009). However, they have also argued that such capacity limits can be overcome, at least temporarily, by excitatory inputs into parietal cortex from prefrontal cortex (Edin et al., 2009). They have suggested that this provides a mechanistic account of top-down control over working memory capacity by prefrontal cortex. As such, given the evidence for at least some types of abnormalities in top-down control of attention in schizophrenia (Fuller et al., 2006; Hahn et al., 2010), and evidence for altered connectivity between prefrontal and parietal regions (Barch and Csernansky, 2007; Karlsgodt et al., 2008), another possible source of reduced capacity in working memory in schizophrenia may be a reduction in prefrontal-mediated excitatory input into parietal networks that maintain items in working memory.
One might argue that the same GABA, glutamate, or dopamine mechanisms thought to impair the maintenance of representations in working memory could also impair the initial establishment of gamma oscillating networks representing items, their coupling to a lower-frequency theta cycle, or even the ability of prefrontal cortex to provide excitatory inputs into neural networks supporting the representation of items in working memory. If so, such models will also need to explain how such impairments could lead to reduced working memory capacity in schizophrenia without a change in precision or decay, a challenge for most current neural network models of working memory. As such, the data provided by Gold and colleagues suggest an exciting new pathway for research on working memory in schizophrenia that may allow us to develop more precise mechanistic hypotheses as to the source of these cognitive impairments and their relationship to pathophysiology of this illness.
Lisman JE, Coyle JT, Green RW, Javitt DC, Benes FM, Heckers S, Grace AA. Circuit-based framework for understanding neurotransmitter and risk gene interactions in schizophrenia. Trends Neurosci. 2008;31(5):234-42. Abstract
Durstewitz D, Seamans JK. The dual-state theory of prefrontal cortex dopamine function with relevance to catechol-o-methyltransferase genotypes and schizophrenia. Biol Psychiatry. 2008;64(9):739-49. Abstract
Rolls ET, Loh M, Deco G, Winterer G. Computational models of schizophrenia and dopamine modulation in the prefrontal cortex. Nat Rev Neurosci. 2008;9(9):696-709. Abstract
Lewis DA, Cho RY, Carter CS, Eklund K, Forster S, Kelly MA, Montrose D. Subunit-selective modulation of GABA type A receptor neurotransmission and cognition in schizophrenia. Am J Psychiatry. 2008;165(12):1585-93. Abstract
Hahn B, Kappenman ES, Robinson BM, Fuller RL, Luck SJ, Gold JM. Iconic Decay in Schizophrenia. Schizophr Bull. 2010. 2010 Jan 6. Abstract
Gold JM, Wilk CM, McMahon RP, Buchanan RW, Luck SJ. Working memory for visual features and conjunctions in schizophrenia. J Abnorm Psychol. 2003;112(1):61-71. Abstract
Fuller RL, Luck SJ, Braun EL, Robinson BM, McMahon RP, Gold JM. Impaired control of visual attention in schizophrenia. J Abnorm Psychol. 2006;115(2):266-75. Abstract
Gold JM, Fuller RL, Robinson BM, McMahon RP, Braun EL, Luck SJ. Intact attentional control of working memory encoding in schizophrenia. J Abnorm Psychol. 2006;115(4):658-73. Abstract
van Raalten TR, Ramsey NF, Jansma JM, Jager G, Kahn RS. Automatization and working memory capacity in schizophrenia. Schizophr Res. 2008;100(1-3):161-71. Abstract
Silver H, Feldman P, Bilker W, Gur RC. Working memory deficit as a core neuropsychological dysfunction in schizophrenia. Am J Psychiatry. 2003;160(10):1809-16. Abstract
Lisman J. Working memory: the importance of theta and gamma oscillations. Curr Biol. 2010;20(11):R490-2. Abstract
Cowan N. The magical number 4 in short-term memory: A reconsideration of mental storage capacity. Behav Brain Sci. 2001;24:87-114. Abstract
Wolters G, Raffone A. Coherence and recurrency: maintenance, control and integration in working memory. Cogn Process. 2008;9(1):1-17. Abstract
Barr MS, Farzan F, Tran LC, Chen R, Fitzgerald PB, Daskalakis ZJ. Evidence for excessive frontal evoked gamma oscillatory activity in schizophrenia during working memory. Schizophr Res. 2010. Abstract
Basar-Eroglu C, Brand A, Hildebrandt H, Karolina Kedzior K, Mathes B, Schmiedt C. Working memory related gamma oscillations in schizophrenia patients. Int J Psychophysiol. 2007;64(1):39-45. Abstract
Light GA, Hsu JL, Hsieh MH, Meyer-Gomes K, Sprock J, Swerdlow NR, Braff DL. Gamma band oscillations reveal neural network cortical coherence dysfunction in schizophrenia patients. Biol Psychiatry. 2006;60(11):1231-40. Abstract
Kissler J, Muller MM, Fehr T, Rockstroh B, Elbert T. MEG gamma band activity in schizophrenia patients and healthy subjects in a mental arithmetic task and at rest. Clin Neurophysiol. 2000;111(11):2079-87. Abstract
Haenschel C, Bittner RA, Waltz J, Haertling F, Wibral M, Singer W, Linden DE, Rodriguez E. Cortical oscillatory activity is critical for working memory as revealed by deficits in early-onset schizophrenia. J Neurosci. 2009;29(30):9481-9. Abstract
Edin F, Klingberg T, Johansson P, McNab F, Tegner J, Compte A. Mechanism for top-down control of working memory capacity. Proc Natl Acad Sci U S A. 2009;106(16):6802-7. Abstract
Compte A, Brunel N, Goldman-Rakic PS, Wang XJ. Synaptic mechanisms and network dynamics underlying spatial working memory in a cortical network model. Cereb Cortex. 2000;10(9):910-23. Abstract
Hahn B, Robinson BM, Kaiser ST, Harvey AN, Beck VM, Leonard CJ, Kappenman ES, Luck SJ, Gold JM. Failure of schizophrenia patients to overcome salient distractors during working memory encoding. Biol Psychiatry. 2010 June 4. Abstract
Barch DM, Csernansky JG. Abnormal parietal cortex activation during working memory in schizophrenia: verbal phonological coding disturbances versus domain-general executive dysfunction. Am J Psychiatry. 2007;164(7):1090-8. Abstract
Karlsgodt KH, van Erp TG, Poldrack RA, Bearden CE, Nuechterlein KH, Cannon TD. Diffusion tensor imaging of the superior longitudinal fasciculus and working memory in recent-onset schizophrenia. Biol Psychiatry. 2008;63(5):512-8. Abstract
View all comments by Deanna M. Barch
Comments on Related News
Related News: Asynchrony and the Brain—Gamma Deficits Linked to Poor Cognitive ControlComment by: Richard Deth
Submitted 14 December 2006
Posted 15 December 2006
Schizophrenia is associated with dopaminergic dysfunction, impaired gamma synchronization and impaired methylation. It is therefore of interest that the D4 dopamine receptor is involved in gamma synchronization (Demiralp et al., 2006) and that the D4 dopamine receptor uniquely carries out methylation of membrane phospholipids (Sharma et al., 1999). A reasonable and unifying hypothesis would be that schizophrenia results from a failure of methylation to adequately support dopamine-stimulated phospholipid methylation, leading to impaired gamma synchronization. Synchronization in response to dopamine can provide a molecular mechanism for attention, as information in participating neural networks is able to bind together to create cognitive experience involving multiple brain regions.
View all comments by Richard Deth
Related News: Asynchrony and the Brain—Gamma Deficits Linked to Poor Cognitive Control
Comment by: Fred Sabb
Submitted 12 January 2007
Posted 12 January 2007
I recommend the Primary Papers
Cho and colleagues find patients with schizophrenia showed a reduction in induced gamma band activity in the dorsolateral prefrontal cortex compared to healthy control subjects during a behavioral task that is known to challenge cognitive control processes. Importantly, the induced gamma band activity was correlated with better performance in healthy subjects, and negatively correlated with higher disorganization symptoms in patients with schizophrenia. These findings help explain previous post-mortem evidence of disruptions in thalamofrontocortical circuits in these patients.
These findings tie together several different previously identified phenotypes into a unifying story. The ability to link phenotypes across translational research domains is paramount to understanding complex neuropsychiatric diseases like schizophrenia. Cho and colleagues provide an excellent example for connecting evidence from symptom rating scales with behavioral, neural systems and neurophysiological data. Although not specifically addressed by the authors, these data may have important implications for understanding the neural basis of thought disorder as well. Hopefully, these findings will provide a frame-work for examining more informed and specific phenotypes relevant to schizophrenia.
View all comments by Fred Sabb
Related News: Order in the Cortex: Clozapine Curbs Unruly Networks
Comment by: J David Jentsch
Submitted 16 September 2007
Posted 17 September 2007
The article by Kargieman and colleagues further specifies the cellular mechanisms underlying the actions of clozapine in a model of pharmacologically induced cortical dysfunction. Separately, clozapine has been demonstrated to be capable of reducing or eliminating the complex behavioral and cognitive impairments elicited by acutely administered NMDA antagonists (Geyer et al., 2001; Idris et al., 2005; Lipina et al., 2005), and these cellular mechanisms shown by Kargieman et al. may represent the level of interaction between clozapine and phencyclidine-like drugs.
What is surprising from so many of these studies is the quality of the reversal of effects produced by clozapine, despite the fact that it (like most other antipsychotic drugs) has limited efficacy both at an individual and population level. Furthermore, there remain many reports in the literature demonstrating that while some cognitive and symptomatic domains in schizophrenia are improved by clozapine, others clearly are not (Goldberg and Weinberger, 1996; Bilder et al., 2002). Why, then, is clozapine so effective in the PCP model? One concern, of course, is that its effects are related to a specific type of pharmacological interaction; one certainly needs to see clozapine's effects in other models that do not involve the acute administration of an NMDA antagonist.
Notably, several groups have been studying the effects of long-term administration of phencyclidine, sometimes followed by washout of the NMDA antagonist, to develop an alternative type of model that may depend upon the neuroadaptations resulting from blockade of NMDA receptors, rather than on the acute pharmacological action itself (Jentsch et al., 1997; Balla et al., 2003; Amitai et al., 2007, and many others). Whilst the specific validity of any one of these approaches is debatable, what appears to be clear is that the ability of clozapine to reverse behavioral or neurochemical deficits is much more tenuous. Is this a weakness of these models, or does it mean they are actually more realistic in their predictions?
Based upon these facts, one is left with a number of questions. First, is a model that predicts that clozapine is completely effective at blocking psychopathology or pathophysiology valid? Second, is the action of clozapine in any one model based upon one kind of manipulation really that provocative? And finally (and perhaps most importantly), is developing models that explain how clozapine works really in our best interest, or is it time to move beyond models that predict marginal gains from existing drugs, in order to look to targets flowing from the new valid genetic mechanisms that appear to hold the keys to the next generation of treatments for schizophrenia?
Amitai N, Semenova S, Markou A. Cognitive-disruptive effects of the psychotomimetic phencyclidine and attenuation by atypical antipsychotic medications in rats. Psychopharmacology (Berl). 2007 Sep;193(4):521-37. Abstract
Balla A, Sershen H, Serra M, Koneru R, Javitt DC. Subchronic continuous phencyclidine administration potentiates amphetamine-induced frontal cortex dopamine release. Neuropsychopharmacology. 2003 Jan;28(1):34-44. Abstract
Bilder RM, Goldman RS, Volavka J, Czobor P, Hoptman M, Sheitman B, Lindenmayer JP, Citrome L, McEvoy J, Kunz M, Chakos M, Cooper TB, Horowitz TL, Lieberman JA. Neurocognitive effects of clozapine, olanzapine, risperidone, and haloperidol in patients with chronic schizophrenia or schizoaffective disorder. Am J Psychiatry. 2002 Jun;159(6):1018-28. Abstract
Geyer MA, Krebs-Thomson K, Braff DL, Swerdlow NR. Pharmacological studies of prepulse inhibition models of sensorimotor gating deficits in schizophrenia: a decade in review. Psychopharmacology (Berl). 2001 Jul;156(2-3):117-54. Abstract
Goldberg TE, Weinberger DR. Effects of neuroleptic medications on the cognition of patients with schizophrenia: a review of recent studies. J Clin Psychiatry. 1996;57 Suppl 9:62-5. Abstract
Idris NF, Repeto P, Neill JC, Large CH. Investigation of the effects of lamotrigine and clozapine in improving reversal-learning impairments induced by acute phencyclidine and D-amphetamine in the rat. Psychopharmacology (Berl). 2005 May;179(2):336-48. Abstract
Jentsch JD, Redmond DE Jr, Elsworth JD, Taylor JR, Youngren KD, Roth RH. Enduring cognitive deficits and cortical dopamine dysfunction in monkeys after long-term administration of phencyclidine. Science. 1997 Aug 15;277(5328):953-5. Abstract
Lipina T, Labrie V, Weiner I, Roder J. Modulators of the glycine site on NMDA receptors, D-serine and ALX 5407, display similar beneficial effects to clozapine in mouse models of schizophrenia. Psychopharmacology (Berl). 2005 Apr;179(1):54-67. Abstract
View all comments by J David Jentsch
Related News: Order in the Cortex: Clozapine Curbs Unruly Networks
Comment by: Jeremy Seamans
Submitted 28 September 2007
Posted 28 September 2007
The paper by Kargieman et al. provides an interesting perspective on the effects of PCP on activity in the prefrontal cortex. Dr. Javitt brings up an excellent point in his commentary that the study highlights the importance of PCP in this preparation as a model of slow-wave sleep disturbances in schizophrenia. In anesthetized animals, field potential recordings resemble the up and down states observed in slow-wave sleep. These states are driven by NMDA receptors and, accordingly, NMDA antagonists such as PCP and ketamine should reduce them as reported. The odd thing about NMDA antagonists is that they themselves can be used as anesthetics to produce a state where slow delta oscillations predominate. For instance, robust up and down states or slow oscillations at or below delta are observed when ketamine is used as an anesthetic. Therefore, NMDA antagonists can induce a state where delta activity is prominent, yet if the subject is already in that state, the effect of the drug is to reduce such activity.
So this also may be the case with PCP. There are numerous EEG studies showing that PCP significantly increases activity in the delta band of awake humans or animals (Stockard et al., 1976; Matsuzaki and Dowling, 1985; Mattia et al.,1988; Marquis et al., 1989; Yamamoto, 1997; Sebban et al., 2002), yet reduces power in this band of anesthetized animals. Moreover, schizophrenics appear to have a significant increase in frontal delta oscillations when awake (Wuebben and Winterer, 2001), yet exhibit slow-wave sleep disturbances and lower delta count when asleep (Ganguli et al., 1987). How is that?
It may be a matter of perspective. In the awake state the cortex is highly desynchronized and firing is quite irregular with power in a variety of high-frequency bands and neurons firing at every phase angle of the field potential. With anesthetics, higher frequencies become unsustainable. Using realistic network model simulations, Durstewitz and Gabriel (2007) showed that if you come from a regime which is quite irregular and then reduce NMDA, you get clear delta wave oscillations, but as you keep reducing NMDA, these delta oscillations will become progressively reduced as well. So in the awake state, reductions in NMDA currents should relatively decrease power in many bands yet enhance delta, but if the network is already in delta, as when the subject is anesthetized or asleep, NMDA reduction would decrease power in this band. Therefore, the results of Kargieman et al., when viewed in light of the literature obtained in awake subjects and schizophrenics, confirms a non-trivial and somewhat paradoxical prediction of the NMDA theory of schizophrenia and the PCP model.
Durstewitz D, Gabriel T. Dynamical basis of irregular spiking in NMDA-driven prefrontal cortex neurons.
Cereb Cortex. 2007 Apr;17(4):894-908. Epub 2006 Jun 1.
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View all comments by Jeremy Seamans
Related News: Clozapine: The Safest Antipsychotic?
Comment by: John McGrath, SRF Advisor
Submitted 23 July 2009
Posted 23 July 2009
I recommend the Primary Papers
The results of this study are surprising. In those with schizophrenia, those on clozapine had by far the lowest relative risk of death (compared to patients on other antipsychotics). Compared to older medications, atypical antipsychotics, to date, do not seem to be impacting on the relative risk of death.
I congratulate the authors on this impressive study. The study is another reminder of the utility of population-based record linkage studies. Thank heavens for the Nordic countries' health registers.
A few years ago we wondered if the differential mortality rate for schizophrenia was worsening over time (Saha et al., 2007). In addition to differential access to health care, we worried that the adverse effects of atypical antipsychotics might be a “ticking time bomb” for worsening mortality in the decades to come. The new Finnish study shows a more nuanced picture emerging.
While the results are thought provoking, let’s not forget about the main game. We all agree that there is still much more work to be done in optimizing the general physical health of people with schizophrenia.
Saha S, Chant D, McGrath J. A systematic review of mortality in schizophrenia: is the differential mortality gap worsening over time? Arch Gen Psychiatry . 2007 Oct 1 ; 64(10):1123-31. Abstract
View all comments by John McGrath
Related News: Clozapine: The Safest Antipsychotic?
Comment by: Francine Benes, SRF Advisor
Submitted 4 November 2009
Posted 4 November 2009
Clozapine: A First-Line Antipsychotic?
Tiihonen et al., of the University of Kuopio in Finland, compared mortality rates in over 66,000 patients with schizophrenia with the entire population of Finland and concluded that clozapine should be used as a first-line drug in the treatment of this disorder. Clozapine is a very effective antipsychotic, and for patients who have received it for several years, the improvement in clinical status can be quite remarkable (Lindstrom, 1988; Agid et al., 2008). Additionally, the improved mortality rate of patients on clozapine may be attributable, at least in part, to the close monitoring of their white blood cell count (WBC).
The stipulation that weekly or biweekly blood samples must be drawn is not an issue that can be viewed lightly, because approximately 1-2 percent of patients on clozapine may show significant decreases in their WBC. This may be a harbinger of agranulocytosis, a potentially lethal form of morbidity in which the bone marrow loses its ability to generate leukocytes; death remains a significant risk for patients taking this drug (Taylor et al., 2009). To some, this may seem like a small price to pay for an improved quality of life. For others, however, it represents an unacceptable degree of risk. Additionally, many patients consider the requirement for frequent blood drawing as intrusive and/or painful and refuse to have it done (personal observation).
Perhaps the greatest source of resistance to using clozapine as a “first-line” drug is the psychiatrist who is faced with this decision. In general, most believe that they would be exposing their patient to unnecessary risk and prefer to look toward other, more “benign” antipsychotic drugs (APDs) for treatment options. In practice, however, the second-generation atypical APDs are not necessarily better candidates for “first-line” use, because they may be even more likely to cause excessive weight gain, diabetes mellitus, and cardiovascular disease (Wehring et al., 2003; Henderson et al., 2005) and result in increased mortality (Meatherall and Younes, 2002). In addition to the risk of agranulocytosis, clozapine may also cause unacceptable amounts of sedation, drooling, and weight gain. Typical APDs, on the other hand, are associated with other side effects that can be quite debilitating. These include extrapyramidal movement disorders, such as 1) akathisia, a condition that may cause a worsening of symptoms as a result of agitation; 2) drug-induced Parkinsonism, in which hypokinesia usually complicates the negative symptoms of schizophrenia; and 3) tardive dyskinesia, a syndrome in which there are involuntary movements of the tongue and lips that can result in significant disability and even disfigurement (Peacock et al., 1996).
In considering the choice of an APD for a “first-episode” patient with schizophrenia, all of these factors must be considered. It is impossible to know how a particular patient with no prior history of having taken an APD will respond to any given drug. What may be an excellent “first-line” drug for one patient may not be so for another. So, the choice of a “first-line” drug requires that the doctor and patient work together to identify the APD that is most appropriate at a particular time in the course of the illness, particularly if the patient has a treatment-sensitive or treatment-resistant form of schizophrenia (Wang et al., 2004).
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Henderson DC, Nguyen DD, Copeland PM, Hayden DL, Borba CP, Louie PM, Freudenreich O, Evins AE, Cather C, Goff DC. Clozapine, diabetes mellitus, hyperlipidemia, and cardiovascular risks and mortality: results of a 10-year naturalistic study. J Clin Psychiatry. 2005;66:1116-21. Abstract
Lindstrom LH. The effect of long-term treatment with clozapine in schizophrenia: a retrospective study in 96 patients treated with clozapine for up to 13 years. Acta Psychiatr Scand. 1988;77:524-9. Abstract
Meatherall R, Younes J. Fatality from olanzapine induced hyperglycemia. J Forensic Sci. 2002;47:893-6. Abstract
Peacock L, Solgaard T, Lublin H, Gerlach J . Clozapine versus typical antipsychotics. A retro- and prospective study of extrapyramidal side effects. Psychopharmacology (Berl). 1996; 124:188-96. Abstract
Taylor DM, Douglas-Hall P, Olofinjana B, Whiskey E, Thomas A. Reasons for discontinuing clozapine: matched, case-control comparison with risperidone long-acting injection. Br J Psychiatry. 2009;194:165-7. Abstract
Wang PS, Ganz DA, Benner JS, Glynn RJ, Avorn J. Should clozapine continue to be restricted to third-line status for schizophrenia?: a decision-analytic model. J Ment Health Policy Econ. 2004;7:77-85. Abstract
Wehring HJ, Kelly DL, Love RC, Conley RR. Deaths from diabetic ketoacidosis after long-term clozapine treatment. Am J Psychiatry. 2003;160:2241-2. Abstract
View all comments by Francine Benes
Related News: Clozapine: The Safest Antipsychotic?
Comment by: Edward Orton (Disclosure)
Submitted 18 November 2009
Posted 18 November 2009
I recommend the Primary Papers
Dr. Benes notes that clozapine is "...a very effective antipsychotic, and...improvement in clinical status can be quite remarkable." The mortality figures reported by Tihonen et al. have proved quite striking to schizophrenia researchers. The perception within the psychiatry community that clozapine is too risky for first-line therapy needs further assessment and discussion. Only about 5 percent of schizophrenics in the U.S. receive clozapine (Lieberman, 2009), leaving the vast majority of patients undermedicated because of this perception. The major issue with starting a patient on clozapine is WBC monitoring. I would like to call upon the NIMH to establish a major study in which schizophrenics are introduced to clozapine on an inpatient basis for 30-60 days to establish safety. It is well known that most WBC events associated with clozapine occur in the first few weeks of treatment. Also, I note that current prescribing practice with clozapine actually allows for monthly blood monitoring after 12 months of continuous clozapine use. Thus, the burden of monitoring diminishes sharply after one year.
Lieberman J. A Beacon of Hope: Prospects for Preventing and Recovering from Mental Illness. NARSAD Research Quarterly 2 (1), Winter 2009.
View all comments by Edward Orton
Related News: Study Forges Link Between Neural Oscillations, Working Memory
Comment by: Kevin Spencer (Disclosure)
Submitted 27 May 2014
Posted 27 May 2014
When we look at an EEG recording, we see the summed electrical fields from throughout the brain that are manifestations of various kinds of information processing. Ideally, we would like to understand the actual information processing mechanisms that are manifested by these various neurophysiological phenomena, such as transients (event-related potential components) and oscillations. One of the reasons why there has been such interest in brain oscillations in recent years is that the neural mechanisms underlying some oscillations have been determined to a certain extent. For example, cortical gamma oscillations are generated through the synergistic interactions between pyramidal cells and fast-spiking inhibitory interneurons, whereas some beta oscillations are generated by gap junction-mediated interactions between only pyramidal cells (Kopell et al., 2010). Understanding the relationships between oscillations and the cognitive processes with which they are associated is an important goal of cognitive neuroscience. Furthermore, understanding these relationships would facilitate the use of EEG phenomena such as oscillations as biomarkers of particular cognitive functions that could be useful targets for treatments of neuropsychiatric disorders.
The study by Yamamoto et al. (Yamamoto et al., 2014) represents an advance in revealing the neural mechanisms underlying cognitive functions. Previous work by Tonegawa and colleagues has demonstrated that for mice, spatial working memory is subserved in part by interactions between the entorhinal cortex and the hippocampus (Suh et al., 2011; Kitamura et al., 2014). They found that these interactions occur in a circuit from the upper layers of the medial entorhinal cortex (MEC) to the dorsal CA1 region of the hippocampus and back to layer 5 of the MEC. In this study, Yamamoto et al. identified oscillatory synchronization in the high gamma band (65-120 Hz) between the MEC and CA1 as the mechanism underlying the apparently conscious retrieval of information in working memory. They were able to reach this conclusion not just by observing relationships between behavioral performance and oscillations, but also by manipulating circuit elements with state-of-the-art genetic and optogenetic methods to determine the causal relationships between neural activity in the MEC and CA1.
While this particular information processing mechanism may not be useful as a biomarker in schizophrenia research (as electrophysiological responses in the medial temporal lobe are difficult to detect with non-invasive methods), one can imagine using a similar set of approaches to study, for example, the beta synchronization between prefrontal and parietal cortices that is involved in visual working memory (e.g., Salazar et al., 2012). Knowledge of the exact circuit elements and direction of information flow within this prefrontal-parietal circuit, along with the cognitive function that arises from activity within it, could enable researchers to precisely model its disruption in schizophrenia and determine how best to ameliorate this dysfunction. We are likely to see more such efforts in the future.
Kitamura T, Pignatelli M, Suh J, Kohara K, Yoshiki A, Abe K, Tonegawa S. Island cells control temporal association memory. Science . 2014 Feb 21 ; 343(6173):896-901. Abstract
Kopell N, Kramer MA, Malerba P, Whittington MA. Are different rhythms good for different functions? Front Hum Neurosci . 2010 ; 4():187. Abstract
Salazar RF, Dotson NM, Bressler SL, Gray CM. Content-specific fronto-parietal synchronization during visual working memory. Science . 2012 Nov 23 ; 338(6110):1097-100. Abstract
Suh J, Rivest AJ, Nakashiba T, Tominaga T, Tonegawa S. Entorhinal cortex layer III input to the hippocampus is crucial for temporal association memory. Science . 2011 Dec 9 ; 334(6061):1415-20. Abstract
Yamamoto J, Suh J, Takeuchi D, Tonegawa S. Successful execution of working memory linked to synchronized high-frequency gamma oscillations. Cell . 2014 May 8 ; 157(4):845-57. Abstract
View all comments by Kevin Spencer