of his study to the phenomena of how speech is understood and produced. through his study, it was discovered and expanded upon that we articulate via the left hemisphere. broca's observations and methods are widely considered to be where neuropsychology really takes form as a recognizable and respected discipline. armed with the understanding that specific, independent areas of the brain are responsible for articulation and understanding of speech, the brains abilities were finally being acknowledged as the complex and highly intricate organ that it is. broca was essentially the first to fully break away from the ideas of phrenology and delve deeper into a more scientific and psychological view of the brain. carl wernicke carl wernicke was an influential nineteenth century neuropsychiatrist specifically interested in understanding how abnormalities could be localized to specific brain regions. previously held theories attributed brain function as one singular process but wernicke was one of the first to attribute brain function to different regions of the brain based on sensory and motor function. in 1873, wernicke observed a patient presenting with poor language comprehension despite maintaining intact speech and hearing following a severe stroke. post-morbid analysis revealed a lesion near the auditory region of the brain in the parietal-temporal region of the left hemisphere. originally named sensory aphasia, this region later became known as wernicke's area. individuals with damage to this area present with fluent but receptive aphasia characterized by the inability to comprehend or express written or spoken language while maintaining intact speech and auditory processes. along with paul broca, wernicke's contributions greatly expanded the present knowledge of language development and localization of left hemispheric function. karl spencer lashley lashley's works and theories that follow are summarized in his book brain mechanisms and intelligence. lashley's theory of the engram was the driving force for much of his research. an engram was believed to be a part of the brain where a specific memory was stored. he continued to use the training/ablation method that franz had taught him. he would train a rat to learn a maze and then use systematic lesions and removed sections of cortical tissue to see if the rat forgot what it had learned. through his research with the rats, he learned that forgetting was dependent on the amount of tissue removed and not where it was removed from. he called this mass action and he believed that it was a general rule that governed how brain tissue would respond, independent of the type of learning. but we know now that mass action was a misinterpretation of his empirical results, because in order to run a maze the rats required multiple cortical areas. cutting into small individual parts alone will not impair the rats' brains much, but taking large sections removes multiple cortical areas at one time, affecting various functions such as sight, motor coordination, and memory, making the animal unable to run a maze properly. lashley also proposed that a portion of a functional area could carry out the role of the entire area, even when the rest of the area has been removed. he called this phenomenon equipotentiality. we know now that he was seeing evidence of plasticity in the brain: within certain constraints the brain has the ability for certain areas to take over the functions of other areas if those areas should fail or be removed - although not to the extent initially argued by lashley. approaches experimental neuropsychology is an approach that uses methods from experimental psychology to uncover the relationship between the nervous system and cognitive function. the majority of work involves studying healthy humans in a laboratory setting, although a minority of researchers may conduct animal experiments. human work in this area often takes advantage of specific features of our nervous system (for example that visual information presented to a specific visual field is preferentially processed by the cortical hemisphere on the opposite side) to make links between neuroanatomy and psychological function. clinical neuropsychology is the application of neuropsychological knowledge to the assessment (see neuropsychological test and neuropsychological assessment), management, and rehabilitation of people who have experienced illness or injury (particularly to the brain) which has caused neurocognitive problems. in particular they bring a psychological viewpoint to treatment, to understand how such illness and injury may affect and be affected by psychological factors. they also can offer an opinion as to whether a person is demonstrating difficulties due to brain pathology or as a consequence of an emotional or another (potentially) reversible cause or both. for example, a test might show that both patients x and y are unable to name items that they have been previously exposed to within the past 20 minutes (indicating possible dementia). if patient y can name some of them with further prompting (e.g. given a categorical clue such as being told that the item they could not name is a fruit), this allows a more specific diagnosis than simply dementia (y appears to have the vascular type which is due to brain pathology but is usually at least somewhat reversible). clinical neuropsychologists often work in hospital settings in an interdisciplinary medical team; others work in private practice and may provide expert input into medico-legal proceedings. cognitive neuropsychology is a relatively new development and has emerged as a distillation of the complementary approaches of both experimental and clinical neuropsychology. it seeks to understand the mind and brain by studying people with brain injuries or neurological illnesses. one model of neuropsychological functioning is known as functional localization. this is based on the principle that if a specific cognitive problem can be found after an injury to a specific area of the brain, it is possible that this part of the brain is in some way involved. however, there may be reason to believe that the link between mental functions and neural regions is not so simple. an alternative model of the link between mind and brain, such as parallel processing, may have more explanatory power for the workings and dysfunction of the human brain. yet another approach investigates how the pattern of errors produced by brain-damaged individuals can constrain our understanding of mental representations and processes without reference to the underlying neural structure. a more recent but related approach is cognitive neuropsychiatry which seeks to understand the normal function of mind and brain by studying psychiatric or mental illness. connectionism is the use of artificial neural networks to model specific cognitive processes using what are considered to be simplified but plausible models of how neurons operate. once trained to perform a specific cognitive task these networks are often damaged or 'lesioned' to simulate brain injury or impairment in an attempt to understand and compare the results to the effects of brain injury in humans. functional neuroimaging uses specific neuroimaging technologies to take readings from the brain, usually when a person is doing a particular task, in an attempt to understand how the activation of particular brain areas is related to the task. in particular, the growth of methodologies to employ cognitive testing within established functional magnetic resonance imaging (fmri) techniques to study brain-behavior relations is having a notable influence on neuropsychological research. in practice these approaches are not mutually exclusive and most neuropsychologists select the best approach or approaches for the task to be completed. methods and tools standardized neuropsychological teststhese tasks have been designed so the performance on the task can be linked to specific neurocognitive processes. these tests are typically standardized, meaning that they have been administered to a specific group (or groups) of individuals before being used in individual clinical cases. the data resulting from standardization are known as normative data. after these data have been collected and analyzed, they are used as the comparative standard against which individual performances can be compared. examples of neuropsychological tests include: the wechsler memory scale (wms), the wechsler adult intelligence scale (wais), boston naming test, the wisconsin card sorting test, the benton visual retention test, and the controlled oral word association. when interpreting neuropsychological testing it is important that the diagnosis is empirically informed in order to determine if the cognitive deficits presented are legitimate. successful malingering and symptom exaggeration can result in substantial benefits for the individual including but not limited to significant financial compensation, injury litigation, disability claims, and criminal sentencing. due to the nature of these potential benefits, it is imperative that malingering is identified in neuropsychological tests in order to avoid making an invalid diagnosis. the slick, sherman, and iverson (1999) criteria for malingered neurocognitive dysfunction (mnd) has pioneered the ability to detect malingering in a variety of performance validity tests (pvt) and symptom validity tests (svt) across multiple neuropsychological contexts and disorders. these tests detect malingering by identifying performance that is below the level of probability for neuropsychological dysfunction. brain scansthe use of brain scans to investigate the structure or function of the brain is common, either as simply a way of better assessing brain injury with high resolution pictures, or by examining the relative activations of different brain areas. such technologies may include fmri (functional magnetic resonance imaging) and positron emission tomography (pet), which yields data related to functioning, as well as mri (magnetic resonance imaging), computed axial tomography (cat or ct), and diffusion tensor imaging (dti) which yields structural data. global brain projectbrain models based on mouse and monkey have been developed based on theoretical neuroscience involving working memory and attention, while mapping brain activity based on time constants validated by measurements of neuronal activity in various layers of the brain. these methods also map to decision states of behavior in simple tasks that involve binary outcomes. electrophysiologythe use of electrophysiological measures designed to measure the activation of the brain by measuring the electrical or magnetic field produced by the nervous system. this may include electroencephalography (eeg) or magneto-encephalography (meg). experimental tasksthe use of designed experimental tasks, often controlled by computer and typically measuring reaction time and accuracy on a particular tasks thought to be related to a specific neurocognitive process. an example of this is the cambridge neuropsychological test automated battery (cantab) or cns vital signs (cnsvs).