Schizophrenia is characterized by a multiplicity of symptoms arising from almost all domains of mental function, e.g. language,  emotion,  reasoning,  motor activity and perception.

These symptoms vary between patients, creating very diverse symptom profiles. The symptoms can include experiencing false perceptions (hallucinations), having false beliefs of control or danger (delusions), expressing disorganized speech and behaviour (positive formal thought disorder,  bizarre behaviour), having impaired goal-directed behaviour (avolition), exhibiting blunted affect, being unable to find pleasure in activities or in the company of others (anhedonia/asociality), poverty of speech and thought (alogia) and impaired attention. The symptoms are often divided into positive and negative.  Positive symptoms reflect an excess or distortion of normal function (e.g. hallucinations and delusions),  while negative symptoms reflect a diminution or loss of normal function (e.g. flattening of affect and poverty of speech).

History of positive and negative symptoms

The nineteenth century English physicians John Russell Reynolds and John Hughlings Jackson first used the terms ‘positive’ and ‘negative’.

Reynolds (1858, 1861) discussed positive and negative symptoms within the context of epilepsy in a descriptive and theoretical way. Jackson (1931) suggested that they should be understood in terms of inhibitory processes. (The temporal relationship of these publications is misleading because Jackson was Reynolds’ contemporary, but his works were published posthumously.)

Disease is said to ‘cause’ the symptoms of insanity. I submit that disease only produces negative mental symptoms, answering to the dissolution, and that all elaborate positive mental symptoms (illusions, hallucinations, delusions, and extravagant conduct) are the outcome of activity of nervous elements untouched by any pathological process; that they arise during activity on the lower level of evolution remaining.

Jackson (1931) believed that the florid positive symptoms were a release phenomenon, occurring when underlying brain processes become disinhibited as a result of a pathological insult to a higher level of brain functioning, while negative symptoms represented a more generalized loss of functions.

While many of the pioneers of psychiatric phenomenology recognized the importance of negative symptoms, they did not use this term. For example, Emil Kraepelin wrote extensively about avolition and affective flattening as central and defining features of ‘dementia praecox’.

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There are apparently two principal groups of disorders that characterize the malady. On the one hand we observe a weakening of those emotional activities which permanently form the mainsprings of volition…  Mental activity and instinct for occupation become mute. The result of this highly morbid process is emotional dullness, failure of mental activities, loss of mastery over volition, of endeavour, and ability for independent action…  The second group of disorders consists in the loss of the inner unity of activities of intellect, emotion, and volition in themselves and among one another…. The near connection between thinking and feeling, between deliberation and emotional activity on the one hand, and practical work on the other is more or less lost. Emotions do not correspond to ideas. The patient laughs and weeps without recognizable cause, without any relation to their circumstances and their experiences, smile as they narrate a tale of their attempted suicide. (Kraepelin 1919, pp. 74 - 75)
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Eugen Bleuler (1911/1950) spoke of the ‘group of schizophrenias’, but argued that a single defining feature was present in all people suffering from the illness. This feature, a disturbance in the ability to formulate coherent thought and language (often referred to as ‘thought disorder’ or ‘loose associations’), was the most important of the ‘fundamental symptoms’. Bleuler considered these ‘fundamental symptoms’ to be present in all patients: loss of continuity of associations, loss of affective responsiveness, loss of attention, loss of volition, ambivalence and autism.

Bleuler held that these symptoms reflect underlying abnormalities in basic cognitive and emotive processes, while he relegated hallucinations and delusions to the status of ‘accessory’  or secondary symptoms.

Certain symptoms of schizophrenia are present in every case and in every period of the illness even though, as with every other disease symptom, they must have attained a certain degree of intensity before they can be recognized with any certainty…  Besides the specific permanent or fundamental symptoms, we can find a host of other, more accessory manifestations such as delusions, hallucinations, or catatonic symptoms…  As far as we know, the fundamental symptoms are characteristic of schizophrenia, while the accessory symptoms may also appear in other types of illness. (Bleuler 1911/1950, p. 13)

Kurt Schneider (1959) changed the focus of schizophrenia symptomatology with his assertion that the fundamental symptoms of schizophrenia reflect an inability to define the boundaries between self and non-self, resulting in experiences such as voices conversing or commenting, delusions of control or passivity, and thought withdrawal or insertion. He posited that these easily identifiable florid positive symptoms,  which he called ‘first rank symptoms’, were the defining characteristics of schizophrenia (Schneider 1959). The clinical definition of schizophrenia shifted at this point to an emphasis on these positive or Schneiderian first-rank symptoms. A series of diagnostic tools were developed, such as the Present State Examination (Wing 1970), the Schedule for Affective Disorders and Schizophrenia (Endicott & Spitzer 1978), Research Diagnostic Criteria (Spitzer et al. 1978) and the DSM-III (American Psychiatric Association 1980), which defined schizophrenia according to a narrow band of positive symptoms.

However, clinical realties relatively quickly led to a corrective return to Bleulerian and Kraepelinian ideas, reintroduced as an emphasis on the importance of negative symptoms as central to the concept of schizophrenia. With this realization came three types of explanatory models attempting to account for the heterogeneity of the symptom profile in schizophrenia. These models include categorical, dimensional and unitary approaches to schizophrenia. Each model will be described in detail below.

R.L.M. Fuller, S.K. Schultz and N.C. Andreasen
References

• Addington, J. & Addington, D. (1991) Positive and negative symptoms of schizophrenia: their course and relationship over time. Schizophrenia Research 5, 51 - 59.
• Alda, M., Zvolsky, P. & Dvorakova, M. (1991) Study of chronic schizophrenics with positive and negative family histories of psychosis. Acta Psychiatrica Scandinavica 83, 334 - 337.
• American Psychiatric Association (1980) Diagnostic and Statistical Manual of Mental Disorders (DSM-III), 3rd edn. American Psychiatric Association, Washington DC.
• Andreasen, N.C. (1979a) Affective flattening and the criteria for schizophrenia. American Journal of Psychiatry 136, 944 - 947.
• Andreasen, N.C. (1979b) Thought, language, and communication disorders. I. Clinical assessment, definition of terms, and evaluation of their reliability. Archives of General Psychiatry 36, 1315 - 1321.
• Andreasen, N.C. (1979c) Thought, language, and communication
• disorders. II. Diagnostic significance. Archives of General Psychiatry 36, 1325 - 1330.
• Andreasen, N.C. (1983) The Scale for the Assessment of Negative Symptoms (SANS). University of Iowa, Iowa City, IA.
• Andreasen, N.C. (1984) The Scale for the Assessment of Positive Symptoms (SAPS). University of Iowa, Iowa City, IA.
• Andreasen, N.C. (1985) Positive vs. negative schizophrenia: a critical evaluation. Schizophrenia Bulletin 11, 380 - 389.
• Andreasen, N.C. (1997) Linking mind and brain in the study of mental illnesses: a project for a scientific psychopathology. Science 275, 1586 - 1593.
• Andreasen, N.C. (1999) A unitary model of schizophrenia: Bleuler's 'fragmented phrene' as schizencephaly. Archives of General Psychiatry 56, 781 - 787.
• Andreasen, N.C. & Grove, W.M. (1986) Evaluation of positive and negative symptoms in schizophrenia. Psychiatrie and Psychobiologie 1, 108 - 121.
• Andreasen, N.C. & Olsen, S. (1982) Negative versus positive schizophrenia: definition and validation. Archives of General Psychiatry 39, 789 - 794.
• Andreasen, N.C., Olsen, S.A., Smith, M.R., Dennert, J.W. & Smith, M.R. (1982) Ventricular enlargement in schizophrenia: definition and prevalence. American Journal of Psychiatry 139, 297 - 302.
• Andreasen, N.C., Ehrhardt, J.C., Swayze, V.W. II et al. (1990) Magnetic resonance imaging of the brain in schizophrenia: the pathophysiologic significance of structural abnormalities. Archives of General Psychiatry 47, 35 - 44.
• Andreasen, N.C., Flaum, M., Arndt, S. et al. (1991) Positive and negative symptoms: assessment and validity. Negative Versus Positive Schizophrenia (eds A. Marneros, N.C. Andreasen & M.T. Tsuang), pp. 28 - 51. Springer-Verlag Berlin, Heidelberg.
• Andreasen, N.C., Rezai, K., Alliger, R. et al. (1992) Hypofrontality in neuroleptic-naive and in patients with chronic schizophrenia: assessment with xenon-133 single-photon emission computed tomography and the Tower of London. Archives of General Psychiatry 49, 943 - 958.
• Andreasen, N.C., Flashman, L., Flaum, M. et al. (1994) Regional brain abnormalities in schizophrenia measured with magnetic resonance imaging. Journal of the American Medical Association 272, 1763 - 1769.
• Andreasen, N.C., O'Leary, D.S., Cizadlo, T. et al. (1996) Schizophrenia and cognitive dysmetria: a positron-emission tomography study of dysfunctional prefrontal - thalamic - cerebellar circuitry. Procedures of the National Academy of Sciences of the USA 93, 9985 - 9990.
• Andreasen, N.C., Paradiso, S. & O'Leary, D.S. (1998) 'Cognitive dysmetria' as an integrative theory of schizophrenia: a dysfunction in cortical - subcortical - cerebellar circuitry? Schizophrenia Bulletin 24 (2), 203 - 218.
• Andreasen, N.C., Nopoulos, P., O'Leary, D.S. et al. (1999) Defining the phenotype of schizophrenia: cognitive dysmetria and its neural mechanisms. Biological Psychiatry 46, 908 - 920.
• Arndt, S., Alliger, R.J. & Andreasen, N.C. (1991) The distinction of positive and negative symptoms: the failure of a two-dimensional model. British Journal of Psychiatry 158, 317 - 322.
• Arndt, S., Andreasen, N.C., Flaum, M., Miller, D. & Nopoulos, P. (1995) A longitudinal study of symptom dimensions in schizophrenia: prediction and patterns of change. Archives of General Psychiatry 52 (5), 352 - 360.
• Barnes, T.R., Hutton, S.B., Chapman, M.J. et al. (2000) West London first-episode study of schizophrenia: clinical correlates of duration of untreated psychosis. British Journal of Psychiatry 177 (3), 207 - 211.
• Barta, P.E., Pearlson, G.D. & Powers, R.E. (1990) Auditory hallucinations and smaller superior temporal gyrus volume in schizophrenia. American Journal of Psychiatry 147, 1457 - 1462.
• Barta, P.E., Powers, R.E., Aylward, E.H. et al. (1997) Quantitative MRI volume changes in late onset schizophrenia and Alzheimer's disease compared to normal controls. Psychiatry Research 68, 65 - 75.
• Biehl, H., Maurer, K. & Schubart, C. (1986) Prediction of outcome and utilization of medical services in a prospective study of first onset schizophrenics: results of a prospective 5-year follow-up study. European Archives of Psychiatry and Neurological Sciences 236, 139 - 147.
• Bilder, R.M., Mukherjee, S. & Rieder, R.O. (1985) Symptomatic and neuropsychological components of defect states. Schizophrenia Bulletin 11, 409 - 491.
• Bleuler, E. (1911/1950) Dementia Praecox or the Group of Schizophrenias. Translated by J. Zinkin. International Universities Press, New York.
• Braff, D.L. (1989) Sensory input deficits and negative symptoms in schizophrenic patients. American Journal of Psychiatry 146, 1006 - 1011.
• Braff, D.L. (1993) Information processing and attention dysfunctions in schizophrenia. Schizophrenia Bulletin 19, 233 - 259.
• Breier, A., Wolkowitz, O.M., Doran, A.R. et al. (1987) Neuroleptic responsivity of negative and positive symptoms in schizophrenia. American Journal of Psychiatry 144 (12), 1549 - 1555.
• Breier, A., Schreiber, J. & Dyer, J. (1991) National Institute of Mental Health longitudinal study of chronic schizophrenia: prognosis and predictors of outcome. Archives of General Psychiatry 48, 239 - 246.
• Brown, K. & White, T. (1992) Syndromes of chronic schizophrenia and some clinical correlates. British Journal of Psychiatry 161, 317 - 322.
• Buchsbaum, M.S., Yang, S., Hazlett, E. et al. (1997) Ventricular volume and asymmetry in schizotypal personality disorder and schizophrenia assessed with magnetic resonance imaging. Schizophrenia Research 27, 45 - 53.
• Carpenter, W.T. & Kirkpatrick, B. (1988) The heterogeneity of the longterm course of schizophrenia. Schizophrenia Bulletin 14, 645 - 659.
• Carpenter, W.T., Strauss, J.S. & Bartko, J.J. (1985) On the heterogeneity of schizophrenia. In: Controversies in Schizophrenia (ed. M. Alpert), pp. 25 - 37. Guildford Press, New York.
• Cohen, M.B., Lake, R.R., Graham, L.S. et al. (1989) Quantitative iodine-123 IMP imaging of brain perfusion in schizophrenia. Journal of Nuclear Medicine 30 (10), 1616 - 1620.
• Cornblatt, B.A., Lenzenweger, M.F. & Dworkin, R.H. (1985) Positive and negative schizophrenic symptoms: attention and information processing. Schizophrenia Bulletin 11, 397 - 407.
• Craig, T.J., Bromet Fennig, E.J., Tanenberg-Karant, S., Lavelle, M. & Galambos, J. (2000) Is there an association between duration of untreated psychosis and 24-month clinical outcome in a first-admission series? American Journal of Psychiatry 157, 60 - 66.
• Crow, T.J. (1980) Molecular pathology of schizophrenia: more than one disease process? British Medical Journal 280, 66 - 68.
• Crow, T.J., Corsellis, J.A.N., Cross, A.J. et al. (1981) The search for changes underlying the type II syndrome. In: Biological Psychiatry (eds C. Perris, G. Struwe & B. Jansson), pp. 727 - 731. Elsevier North-Holland Biomedical Press, Amsterdam,
• Cuesta, M. & Peralta, V. (1995) Cognitive disorders in the positive, negative and disordered syndromes of schizophrenia. Psychiatry Research 58, 227 - 235.
• Dewan, M.J., Pandurangi, A.K., Lee, S.H. et al. (1983) Central brain morphology in chronic schizophrenic patients: a controlled CT study. Biological Psychiatry 18 (10), 1133 - 1140.
• Dworkin, R.H., Lenzenweger, M.F. & Moldin, S.O. (1988) A multidimensional approach to the genetics of schizophrenia. American Journal of Psychiatry 145, 1077 - 1083.
• Endicott, J. & Spitzer, R.L. (1978) A diagnostic interview: the Schedule for Affective Disorders and Schizophrenia (SADS). Archives of General Psychiatry 35, 837 - 844.
• Fenton, W.S. & McGlashan, T.H. (1987) Sustained remission in drugfree schizophrenic patients. American Journal of Psychiatry 144, 1306 - 1309.
• Fenton, W.S. & McGlashan, T.H. (1992) Testing systems for assessment of negative symptoms in schizophrenia. Archives of General Psychiatry 49, 179 - 184.
• Freedman, R. (1998) Basic and clinical approaches to the genetics of deficits in schizophrenia. Biological Psychiatry 43 (Suppl. 8), 3.
• Friston, K.J., Liddle, P.F., Frith, C.D., Hirsch, S.R. & Frackowiak, R.S. (1992) The left medial temporal region and schizophrenia: a PET study. Brain 115 (2), 367 - 382.
• Frith, C.D. (1992) The Cognitive Neuropsychology of Schizophrenia. Lawrence Erlbaum, East Sussex.
• Frith, C.D., Friston, K., Liddle, P.F. & Frackowiak, R.S. (1991) Willed action and the prefrontal cortex in man: a study with PET. Proceedings of the Royal Society of London 244, 241 - 246.
• Gaebel, W., Ulrich, G. & Frick, K. (1987) Visuomotor performance of schizophrenic patients and normal controls in a picture viewing task. Biological Psychiatry 22 (10), 1227 - 1237.
• Goldman-Rakic, P.S. (1994) Working memory dysfunction in schizophrenia. Journal of Neuropsychiatry and Clinical Neuroscience 64, 348 - 357.
• Gur, R.E., Mozley, D., Resnick, S.M. et al. (1991) Relations among clinical scales in schizophrenia. American Journal of Psychiatry 148, 472 - 478.
• Ho, B.-C., Andreasen, N.C., Flaum, M., Nopoulos, P. & Miller, D. (2000) Untreated initial psychosis: its relation to quality of life and symptom remission in first-episode schizophrenia. American Journal of Psychiatry 157, 808 - 815.
• Hull, J.W., Smith, T.E., Anthony, D.T. et al. (1997) Patterns of symptom change: a longitudinal analysis. Schizophrenia Research 24, 17 - 18.
• Inoue, K., Nakajima, T. & Kato, N. (1986) A longitudinal study of schizophrenia in adolescence. I. The 1- to 3-year outcome. Japanese Journal of Psychiatry and Neurology 40, 143 - 151.
• Jackson, J.H. (1931) Selected Writings. Hodder and Stoughton, London.
• Jernigan, T.L., Sargent, T. III, Pfefferbaum, A., Kusubov, N. & Stahl,
• S.M. (1985) 18Fluorodeoxyglucose PET in schizophrenia. Psychiatry Research 16 (4), 317 - 329.
• Johnstone, E.C., Crow, T.J., Frith, C.D., Husband, J. & Kreel, L. (1976)
• Cerebral ventricular size and cognitive impairment in chronic schizophrenia. Lancet 2, 924 - 926.
• Johnstone, E., Frith, C. & Gold, A. (1979) The outcome of severe acute schizophrenic illnesses after 1 year. British Journal of Psychiatry 134, 28 - 33.
• Johnstone, E.C., Owens, D.G.C. & Frith, C.D. (1986) The relative stability of positive and negative features in chronic schizophrenia. British Journal of Psychiatry 150, 60 - 64.
• Kay, S.R., Opler, L.A. & Fiszbein, A. (1986) Significance of positive and negative symptoms in chronic schizophrenia. British Journal of Psychiatry 149, 439 - 448.
• Keefe, R., Mohs, R. & Losonczy, M. (1987) Characteristics of very poor outcome schizophrenia. American Journal of Psychiatry 144, 889 - 895.
• Keilp, J.G., Sweeney, J.A., Jacobsen, P. et al. (1988) Cognitive impairment in schizophrenia: specific regions to ventricular size and negative symptomatology. Biological Psychiatry 24, 47 - 55.
• Kendler, K., Myers, J., O'Neill, A. et al. (2000) Clinical features of schizophrenia and linkage to chromosomes 5q, 6p, 8p, and 10p in the Irish study of high-density schizophrenia families. American Journal of Psychiatry 157 (3), 402 - 408.
• Knight, R.A., Roff, J.D., Barnet, J. & Moss, J.L. (1979) Concurrent and predictive validity of thought disorder and affectivity: a 22-year follow-up of acute schizophrenia. Journal of Abnormal Psychology 88, 1 - 12.
• Knights, A. & Hirsch, S.R. (1981) 'Revealed' depression and drug treatment for schizophrenia. Archives of General Psychiatry 38, 806 - 811.
• Kolakowska, T., Williams, A.O. & Ardern, M. (1985) Schizophrenia with good and poor outcome. I. Early clinical features, response to neuroleptics and signs of organic dysfunction. British Journal of Psychiatry 146, 229 - 239.
• Kraepelin, E. (1919) Dementia Praecox and Paraphrenia. Translated by R.M. Barkley. E. & S. Livingstone, Edinburgh.
• Kulhara, P., Kota, S.K. & Joseph, S. (1986) Positive and negative subtypes of schizophrenia: a study from India. Acta Psychiatrica Scandinavica 74, 353 - 359.
• Liddle, P. (1987a) Schizophrenia symptoms, cognitive performance and neurological dysfunction. Psychological Medicine 17, 49 - 57.
• Liddle, P. (1987b) The symptoms of chronic schizophrenia: a reexamination of the positive - negative dichotomy. British Journal of Psychiatry 151, 145 - 151.
• Liddle, P. & Morris, D. (1991) Schizophrenic syndromes and frontal lobe performance. British Journal of Psychiatry 158, 340 - 345.
• Liddle, P., Friston, K.J. & Frith, C.D. (1992) Cerebral blood flow and mental processes in schizophrenia. Journal of the Royal Society of Medicine 85, 224 - 226.
• Lindenmayer, J.P., Kay, S.R. & Friedman, C. (1986) Negative and positive schizophrenic syndromes after the acute phase: a prospective follow-up. Comprehensive Psychiatry 27, 276 - 286.
• Lo, W.H. & Lo, T. (1977) A 10-year follow-up study of Chinese schizophrenics in Hong Kong. British Journal of Psychiatry 131, 63 - 66.
• McGuffin, P. & Owen, M. (1991) The molecular genetics of schizophrenia: an overview and forward view. European Archives of Psychiatry and Clinical Neuroscience 240, 169 - 173.
• Malaspina, D., Goetz, R.R., Yale, S. et al. (2000) Relation of familial schizophrenia to negative symptoms but not to the deficit syndrome. American Journal of Psychiatry 157, 994 - 1003.
• Marneros, A., Deister, A. & Rohde, A. (1991) Stability of diagnoses in affective, schizoaffective and schizophrenic disorders: cross-sectional versus longitudinal diagnosis. European Archives of Psychiatry and Clinical Neuroscience 241, 1870 - 1192.
• Merriam, A.E., Kay, S.R. & Opler, L.A. (1990) Neurological signs and the positive - negative dimension in schizophrenia. Biological Psychiatry 28, 181 - 192.
• Miller, D.D., Arndt, S.V. & Andreasen, N.C. (1993) Alogia, attentional impairment, and inappropriate affect: their status in the dimensions of schizophrenia. Comprehensive Psychiatry 34, 221 - 226.
• Minas, I.H., Stuart, G.W., Klimidis, S. et al. (1992) Positive and negative symptoms in the psychoses: multidimensional scaling of SAPS and SANS items. Schizophrenia Research 8, 143 - 156.
• Munk-Jorgensen, P. & Mortensen, P.B. (1989) Schizophrenia: a 13-year follow-up - diagnostic and psychopathological aspects. Acta Psychiatrica Scandinavica 79, 391 - 399.
• Nelson, M.D., Saykin, A.J., Flashman, L.A. & Riordan, H.J. (1998) Hippocampal reduction in schizophrenia as assessed by magnetic resonance imaging: a meta-analytic study. Archives of General Psychiatry 55 (5), 433 - 440.
• O'Leary, D., Flaum, M., Kesler, M. et al. (2000) Cognitive correlates of the negative, disorganized, and psychotic symptom dimensions of schizophrenia. Journal of Neuropsychiatry and Clinical Neurosciences 12, 4 - 15.
• Pearlson, G.D., Garbacz, D.J. & Moberg, P.J. (1985) Symptomatic, familial, perinatal, and social correlates of computerized axial tomography (CAT) changes in schizophrenics and bipolars. Journal of Nervous and Mental Disorders 173, 42 - 50.
• Pfohl, B. & Winokur, G. (1982) The evolution of symptoms in institutionalized hebephrenic/catatonic schizophrenics. British Journal of Psychiatry 141, 567 - 572.
• Pogue-Geile, M.F. & Harrow, M. (1984) Negative and positive symptoms in schizophrenia and depression: a follow up. Schizophrenia Bulletin 10, 371 - 387.
• Pogue-Geile, M.F. & Harrow, M. (1985) Negative symptoms in schizophrenia: their longitudinal course and prognostic importance. Schizophrenia Bulletin 11, 427 - 439.
• Portas, C.M., Goldstein, J.M., Shenton, M.E. et al. (1998) Volumetric evaluation of the thalamus in schizophrenic male patients using MRI. Biological Psychiatry 43 (9), 649 - 659.
• Post, R.M., DeLisi, L.E., Holcomb, H.H. et al. (1987) Glucose utilization in the temporal cortex of affectively ill patients: positron emission tomography. Biological Psychiatry 22 (5), 545 - 553.
• Reynolds, J. (1858) On the pathology of convulsions, with special reference to those of children. Liverpool Medico-chirurgie Journal 2, 1 - 14.
• Reynolds, J. (1861) Epilepsy: its Symptoms, Treatment and Relation to Other Chronic Convulsive Diseases, Vol. 2. John Churchill, London.
• Roff, J.D. & Knight, R. (1978) A schizophrenia checklist: reliability without stability, concurrent without predictive validity. Psychological Report 43, 791 - 794.
• Schmahmann, J. (1991) An emerging concept: the cerebellar contribution to higher function. Archives of Neurology 48, 1178 - 1187.
• Schneider, K. (1959) Clinical Psychopathology. Translated by M.W. Hamilton. Grune & Stratton, New York.
• Schroeder, J., Buchsbaum, M.S., Siegel, B.V., Geider, F.J. & Niethammer, R. (1995) Structural and functional correlates of subsyndromes in chronic schizophrenia. Psychopathology 28, 38 - 45.
• Scully, P.J., Coakley, G., Kinsella, A. & Waddington, J.L. (1997)
• Psychopathology, executive (frontal) and general cognitive impairment in relation to duration of initially untreated versus subsequently treated psychosis in chronic schizophrenia. Psychological Medicine 27, 1303 - 1310.
• Shenton, M., Kikinis, R. & Jolesz, F. (1992) Abnormalities of the left temporal lobe and thought disorder in schizophrenia: a quantitative magnetic resonance imaging study. New England Journal of Medicine 327, 604 - 612.
• Siris, S.G. (1991) Diagnosis of secondary depression in schizophrenia: implications for DSM-IV. Schizophrenia Bulletin 17, 75 - 98.
• Spitzer, R., Endicott, J. & Robins, E. (1978) Research Diagnostic Criteria (RDC) for a Selected Group of Functional Disorders, Biometrics Research, 3rd edn. New York State Psychiatric Institute, New York.
• Stephens, J.H. (1978) Long-term prognosis and follow-up in schizophrenia. Schizophrenia Bulletin 4, 25 - 47.
• Strauss, J. & Carpenter, W.T. (1974) Characteristic symptoms and outcome in schizophrenia. Archives of General Psychiatry 30, 429 - 434.
• Tamminga, C.A., Thaker, G.K., Buchanan, R.W. et al. (1992)
• Limbic-system abnormalities identified in schizophrenia using positron emission tomography with fluorodeoxyglucose and neocortical alternations with deficit syndrome. Archives of General Psychiatry 49, 522 - 530.
• Vaillant, G. (1978) A 10-year followup of remitting schizophrenics. Schizophrenia Bulletin 4, 78 - 85.
• Volkow, N.D., Wolf, A.P., Van Gelder, P. et al. (1987) Phenomenological correlates of metabolic activity in 18 patients with chronic schizophrenia. American Journal of Psychiatry 144 (2), 151 - 158.
• Waddington, J.L., Youssef, H.A. & Kinsella, A. (1995) Sequential cross-sectional and 10-year prospective study of severe negative symptoms in relation to duration of initially untreated psychosis in chronic schizophrenia. Psychological Medicine 25, 849 - 857.
• Wassink, T., Flaum, M., Nopolous, P. & Andreasen, N. (1999) Prevalence of depressive symptoms early in the course of schizophrenia. American Journal of Psychiatry 156, 315 - 316.
• Weinberger, D.R., Bigelow, L.B., Kleinman, J.E. et al. (1980) Cerebral ventricular enlargement in chronic schizophrenia: an association with poor response to treatment. Archives of General Psychiatry 37, 11 - 13.
• Wing, J.K. (1970) A standard form of psychiatric Present State Examinations (PSE): a method for standardizing the classification of symptoms. In: Psychiatric Epidemiology (eds E.H. Hare & J.K. Wing). Oxford University Press, London.
• Wolkin, A., Sanfilipo, M., Wolf, A.P. et al. (1992) Negative symptoms and hypofrontality in chronic schizophrenia. Archives of General Psychiatry 49 (12), 959 - 965.
• Wyatt, R.J., Green, M.F. & Tuma, A.H. (1997) Long-term morbidity associated with delayed treatment of first admission schizophrenic patients: a re-analysis of the Camarillo State Hospital data. Psychological Medicine 27, 261 - 268.