Schizophrenia Research Trends

80Guy SandnerBOX 2Cognitive Sciences, A Unified Model of Brain FunctionWe shall consider a list of cognitive functions and examine whether each of them isaltered or preserved in patients. But before, a short description is needed on how “CognitiveSciences” model what happens in the brain. It is a theoretical frame that may be appliedsimultaneously to psychology, neurobiology and computer sciences. The essential idea liesin the belief that the brain manages a coherent internal representation of the actual world.The ongoing sensory-motor experiences feed that representation. The brain is also in chargeof holding that representation coherent. Coherency means that memories remain linked toeach other according to their sequence, hierarchy and semantic relationship. For example inan Irish coffee, the cream remains above the coffee, itself above the whisky. This is acommon example of natural hierarchy, picked up by our eyes. Eischenbaum [55] hasproposed that 1) an ordered topographical reference can serve as a prototype for therepresentation of any other order relationship and 2) that the functional properties of thehippocampus are essential for the coherence of mental representations. Some sensations gooften with others, what is an example of externally imposed semantic coherence. Evocationof “winter” goes with the feeling of cold, being surrounded by snow, lack of leaves on thetrees, frozen water. If we are actually in winter, the representation is congruent with ourenvironment and new aspects can become linked to the previously stored ones. On theopposite, the lack of congruence would trigger arousal. In our example, this would occur ifwe read “April” on a calendar. This example means that the representation is continuouslycompared to the external world (except during deep sleep). Based on the results of thecomparison, the representation may be modified (covert action), or the brain may act on thereal world (overt action: set the calendar appropriately in the example given above). Therepresentation is also used to simulate actions and their outcomes [121]. To that end, thebrain includes a “management” function, called “executive system”.BOX 3A Putative Cause of the Alteration of Attention in PatientsAn interesting general description of basic trends of behavior proposed by Dunn hasbeen recently applied to schizophrenia [21]. This model accounts for the feeling that thedifficulty of patients to manage their attention is a byproduct of some more generalalteration of their sensitivity to the environment. Dunn suggested that two orthogonal, i.e. insome sense independent, behavioral tendencies govern our sensitivity to changes in theenvironment. One tendency was called “neurological threshold”. The other tendencyconcerns the possibility to “counter the neurological threshold changes”. These tendencieswere presented in a four quadrant table. Low neurological threshold (supersensitivity to theenvironment) would elicit an overflow of the brain by sensory information. The opposite,