Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Intern. J. Neuroscience, 113:1505–1523, 2003 Copyright  Taylor & Francis Inc. ISSN: 0020-7454 / 1543-5245 online DOI: 10.1080/00207450390231545 ACALCULIA: AN fMRI STUDY WITH IMPLICATIONS WITH RESPECT TO BRAIN PLASTICITY BYRON BERNAL Neurologist, Miami Children’s Hospital Department of Radiology Miami, Florida, USA ALFREDO ARDILA Neuropsychologist, Memorial Regional Hospital Hollywood, Florida, USA NOLAN R. ALTMAN Neuroradiologist, Chief, Department of Radiology Miami Children’s Hospital Miami, Florida, USA We report the case of a 44-year-old right-handed man with severe acalculia and 4 normal age-matched controls. The acalculia patient had magnetic resonance findings of a wedge shaped defect in the left posterior temporal-parietal cortex, involving the angular gyrus, and a lacunar infarct of the right thalamus. Functional magnetic resonance exams were performed utilizing four tasks consisting of serial subtracting by sevens, basic calculation, complex calculation, and abstract calculation. Both patient and controls showed specific task-related activation Received 3 March 2003. Our sincere gratitude to Dr. Mauricio Concha and Dr. Monica Rosselli for their significant contribution when studying this case and for their valuable suggestions; to Dr. Rosario Rosales for her invaluable help with the bibliography work-up and review of the article. Address correspondence to Nolan R Altman, MD, Miami Children’s Hospital, Department of Radiology, 3100 SW 62nd Avenue, Miami, Florida 33155-3009, USA. E-mail: nolan.altman@ MCH.com 1505 1506 B. Bernal et al. with some differences that may indicate brain plasticity, even though no significant recovery in calculations abilities was observed in the patient. Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Keywords acalculia, brain, calculations, fMRI, functional, plasticity Brain plasticity is defined as the ability of the circuitry of the brain to reorganize in response to a neural insult (Kaas, 1991; Simos et al., 2000). From this definition there is no causal relationship between mutability of neural tissue and recovery. Brain plasticity may involve pathway-redundancy, changes in synaptic strength, growth of new synapses, assumption of function by contralateral homologous cortex, and substitution of uncrossed pathways (Frackowiak, 1996; Lee & van Donkelaar, 1995). These brain capabilities usually occur early in immature brains, but may be observed even late in adulthood (Kennard, 1940; Nass, 1984; Vargha-Khadem et al., 1985; Chollet et al., 1991). Thus, the neuronal circuitry involved in a specific function may possibly be shifted, displaced, or relocated after an insult. Brain plasticity has been investigated by functional magnetic resonance imaging (Rossini et al., 1998; Musso et al., 1999; Thulborn et al., 1999; Cao et al., 1999) and positron emission tomography (Chollet et al., 1991; Weiller et al., 1995), in patients with brain lesions and cognitive impairments. These studies correlate changes in brain activation to recovery of the lost function. However, no studies have addressed the functional changes that can occur in the brain not related to recovery. The understanding of these “non-successful” changes can contribute to the knowledge of functional recovery. Functional magnetic resonance (fMR), a current tool used to map brain activity related to motor, sensory, and cognitive tasks, is based on the chemical and vascular changes produced by brain cortical activity. These minute tissue changes occur locally and modify the signal of the MR images. fMRI has been utilized to study brain plasticity in patients after stroke. These studies have focused on different types of brain functions: motor (Rijntjes et al., 1994; Weiller et al., 1993; Maegaki et al., 1995; Rossini et al., 1998), sensory (Maegaki et al., 1995), and language (Weiller et al., 1995; Heiss et al., 1999; Musso et al., 1999; Cappa et al., 1997; Cao et al., 1999). To our knowledge, no prior investigations with functional images Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Acalculia and Brain Plasticity 1507 have addressed brain plasticity in acalculia, a term that defines the loss or impairment in computation ability. Similar to language, calculation relies on a multi-modular network involving frontal and parietal lobes of both hemispheres (Fulbright et al., 2000), with important nodes located primarily in the left posterior parietal areas (Stanescu-Cosson et al., 2000). The understanding of brain plasticity in calculation is important, as calculation is a category-specific model less dependent on language input modalities (Le Clec’H et al., 2000). Despite recent knowledge gained from functional and lesional models, whether there is reorganization without recovery still remains an unanswered question. We present a case in which a righthanded patient, who suffered a left parietal stroke, showed rightparietal activation without significant recovery of the lost arithmetic skills. As in other reports with different cognitive deficits (Weiller et al., 1993; Weiller et al., 1995), the normal activation is assumed from results in normal volunteers, reported in the literature, and from our own service. MATERIALS AND METHODS The patient is a 44-year-old right-handed man, who suffered a stroke during abdominal surgery five years prior to the exam. He complains of difficulty in controlling his right hand, using numerical information, and solving arithmetic problems. Magnetic resonance imaging (MRI) demonstrated a wedge shaped defect in the left posterior temporal-parietal cortex, involving the angular gyrus, and a lacunar infarct of right thalamus (Figure 1). Neuropsychological evaluation showed no important language deficits (Table 1). Mild difficulties were found in right-left orientation and finger gnosis. Reading was normal but in writing (spontaneous and by dictation) a significant number of word omissions and, to a lesser degree, additions were noted (Figure 2). The significant findings were limited to the mathematical domain. The patient was able to count forward, but not backward. He could perform simple one-digit additions (e.g., 5 + 3), but failed all other mathematical tests, including serial additions and subtractions, Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1508 B. Bernal et al. FIGURE 1. Axial T1 weighted MRI of the brain shows generalized atrophy with involvement of cortical and subcortical white matter. A chronic infarct in the left parietaloccipital junction and lacunar right thalamic infarct is seen. multiplying, and dividing. Solving arithmetical problems (e.g., “how many books are there in two dozen and a half?”) was impossible. Similar difficulties were observed in oral and written calculations. However, he preserved the ability to calculate grossly the answer Acalculia and Brain Plasticity 1509 TABLE 1. Language evaluation of the acalculia patient Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Language testing Boston Naming Test Multilingual Aphasia Examination Visual naming Sentence repetition Controlled oral word association Token test Reading comprehension WAIS-III Vocabulary Similarities Digit span Information Comprehension Raw score Standard score* 56 50 56 12 23 39 17 64 43 5 15 17 43 16 14 20 15 9 7 8 11 7 *Standard scores rfer to percentiles (Boston Naming Test and Multilingual Aphasia Examination or scaled scores (WAIS-III). (e.g., “How much is 15 plus 12?”, “I think 25”). He had significant difficulties in halving and doubling small quantities. He failed in dividing objects (e.g., pencils) into equal groups (e.g., to separate nine pencils in three groups, each one containing the same number of pencils). He could read one and two-digit numbers, but the reading FIGURE 2. Sample of spontaneous writing (“I hope Elian Rodriguez can stay in the United States until he goes to school to finish his education in a country so he can make his own decision about where he wants to live when he is an adult”). Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1510 B. Bernal et al. of numbers with more than three digits was difficult. Omissions (10003 → 1003), and inversions (4908 → 4098) would result. There were no errors in aligning numbers in columns. He could write quantities by dictation. Digit substitutions were noted in translating from verbal to numerical (e.g., twenty-three → 25). Omissions and additions of letters and decomposition errors (e.g., 67 → six seven) were observed when transcoding from numerical to verbal code (Figure 3). Table 2 summarizes the results of the different calculation tests. The patient was examined with fMR imaging. Prior to the study, he was instructed not to move during image acquisition and avoid vocalization or sub-vocalization. He was informed that this was a test involving mathematical skills. He was trained using short paradigms to assure comprehension of the task. We were more interested in the continuation of the task rather than the answer. His performance was known beforehand, and then debriefed after the exam, and we preferred not to ask the patient to verbalize an answer because of the risk of producing head motion. Four healthy adult right-handed males volunteers (age 24–35, mean 27.7), were recruited among coworkers; a signed, written informed consent was obtained that was approved by the Institutional Review Board. The subjects were given the same tasks. This group served as a control. Imaging was performed on a 1.5-T MR scanner (General Electric, Milwaukee, WI, USA. Signa Horizon Echospeed 5X) using FIGURE 3. Transcoding from a numerical to a verbal code. Acalculia and Brain Plasticity 1511 Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. TABLE 2. Results of different calculation test in acalculia patient Calculation ability testing Raw Score interpretation WAIS-III Arithmetic Counting forwards (1 to 20) Backwards (30–20) Reading numbers Writing numbers Transcoding: numerical to a verbal Verbal to a numerical Multiplication tables (table of 3) To complete an arithmetical operation Successive arithmetical operations Adding (l, 4, 7?37) Subtracting (100, 93–86?16) 6 20/20 7/10 4/6 6/6 4/6 4/6 6/10 7/8 (Scaled score = 3) abnormal normal abnormal abnormal normal abnormal abnormal abnormal abnormal (e.g., 23?18 = 30) 7/12 0/12 abnormal abnormal Mental calculation (with two digits) Adding Subtracting Multiplying Dividing 0/4 0/4 0/4 0/4 abnormal abnormal abnormal abnormal Written calculation (with two and three digits) Adding Subtracting Multiplying Dividing Aligning numbers in columns Fractions 0/4 0/4 0/4 0/4 5/5 3/3 adnormal adnormal adnormal adnormal normal normal e.g., “what is larger, one-third or one-fourth?” normal (e.g., “at what temperature does water boil?” normal (e.g., “what is your social security number?” abnormal abnormal abnormal General numerical knowledge 4/4 Personal numeral knowledge 4/4 Numerical problems Halving and doubling small quantities Dividing objects into equal groups 0/5 0/6 0/5 birdcage quadrature-transmit-and-receive head coil designed for whole brain imaging. A series of 16 localizer images were obtained in the sagittal plane. On the basis of these images, ten axial slices were selected to obtain the functional and the anatomic images. The slices were parallel to the plane defined by a line between the basal aspect of the frontal and occipital lobes. The anatomic series were obtained with T1-spin-echo acquisitions, time of repetition/time of echo (TR/TE) of 300/14 ms, field of view (FOV) 240 mm, matrix: 256 × 256, 6 mm slice thickness, and 2 mm gap. The functional images Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1512 B. Bernal et al. with same thickness and gap were obtained using a gradient echosingle shot echo planar imaging sequence with TR/TE/Flip-angle of 3750 ms/60/60°. The FOV was 240 mm, and the matrix 64 × 64 voxels. Each voxel had a volume of 3.75 × 3.75 × 6 mm (84.375 mm3). The experiment consisted of 48 time-points (sets) of 10 images, and 2 extra sets at the beginning of the series, used to obtain the steady-state of the transverse magnetization. The 48 sets were divided in 6 epochs, 3 OFF (baseline or control condition) and 3 ON (activated condition). Starting in OFF, the experiment proceeded switching every 30 s. Thus, each slice was scanned 48 times, resulting in 240 image pairs for comparisons. Four paradigms were applied: (1) serial subtracting by seven, (2) basic calculations, (3) complex calculations, and (4) abstract calculations. Serial subtracting by seven was performed starting at 100 for the first ON epoch, from 50 in the second, and from 75 in the third. Basic calculations consisted of simple addition and subtraction problems of one or two digits avoiding carrying over of numbers (e.g.: 7 – 5 = ?). Complex calculations were problems with the same type of calculations involving two digits and requiring carrying, borrowing, and handling of place values (e.g.: 15 – 7 = ?). Abstract calculations included problems involving rules and concepts related to logical and spatial analysis (e.g.: 2 – ¼ = ?). To prevent motion artifacts, the head was fixed with cushions and taped to the headholder of the table. Problems were displayed with a black font on one horizontal line (e.g.: 23 – 7 = ?) over a white background using a back projector and a semitransparent screen placed at the foot of the imaging table. The image was delivered to the patient by a mirror located over his eyes. Numbers were 3 × 2 cm and the screen was located 200 cm from the mirror. The numbers formed a 0.85° vertical angle with the eyes. Each problem was presented for 3 to 6 s (depending on the complexity of the task and previous experience with volunteers). Two different types of baseline (OFF) conditions were used: (1) counting forward from 1 for the serial subtracting by seven, and (2) reading strings of four elements (letter and digits), randomly mixed, for the remainder of paradigms (e.g., F 2 H 6). These OFF epochs were designed to match attention, ocular motion, visual stimulus, and verbal impute and decoding. The fMRI data were analyzed off-line on a Sun-Ultrasparc work- Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Acalculia and Brain Plasticity 1513 station (Sun Microsystems Inc., CA, USA) using MEDx 3.0 software (Sensor Systems, Inc., VA, USA). The functional images were first analyzed to detect motion, using the Intensity Weighted Method. The images were spatially smoothed with a Gaussian kernel of full-widthat-half-maximum (FWHM) of 10 mm to reduce the noise in the images. Intensity normalization was applied to normalize the signal at each voxel and remove the effects of signal drift. Parametrical statistical maps were obtained in each series using a t-test method. zscores were used as activation reference maps, after thresholding them to an uncorrected p < .0005, corresponding to a z-score of 3.47. Anatomic localization was performed by superimposing the functional images on T1 weighted images at the same slice location. RESULTS AND DISCUSSION Table 3 summarizes the results of the control group. In the patient, the serial subtracting by sevens produced activation in the posterior TABLE 3. fMRI results of the calculation tasks in the control group Paradigm Counting backwards Areas of activation Cases Left middle-inferior frontal gyrus Right middle-inferior frontal gyrus Left posterior inferior parietal lobule (PIPL) (including angular gyrus) Left supplemental motor area (SMA) Left frontal eye field 3 3 3 Basic calculation Right middle frontal gyrus Right caudate nucleus Right SMA Left PIPL (including angular gyrus) Left broca 2 2 2 2 I Complex calculation Left middle-inferior frontal gyrus Left PIPL (including angular gyrus) Right PIPL (including mirror angular gyrus) Left cuneus 4 3 2 2 Abstract calculation Left PIPL (including angular gyrus) Right PIPL (including angular gyrus) Left middle-inferior frontal gyrus Left SMA Right SMA Left > right frontal eye field 4 4 3 2 1 3 3 2 Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1514 B. Bernal et al. aspect of the left temporal lobe (Brodmann’s areas 22 and 37), both middle frontal gyri, left cuneus, and adjacent areas to the left angular gyrus (Figure 4). The basic calculation paradigm elicited activation in right caudate nucleus and right middle frontal gyrus (Figure 5). No significant activation was seen in the complex calculation paradigm. The abstract calculation paradigm produced activation in left middle frontal gyrus, right posterior-inferior-parietal lobule (PIPL), and left frontal eye field (Figure 6). FIGURE 4. fMRI obtained with the serial subtracting by sevens paradigm. Areas represented in green correspond to voxels with p value less than .0005. The greatest activation is seen in the left temporal lobe along the deep portion of the superior and inferior banks of the superior temporal sulcus. These are Brodmann’s area 22 and 37. There is a left side predominance. (See Color Plate I at end of issue.) Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Acalculia and Brain Plasticity 1515 FIGURE 5. fMRI obtained with basic calculation. Color corresponds to activation in voxels with p value less than .0005. The main activation is seen in the right caudate nucleus. Notice the lack of activation in the left hemisphere. (See Color Plate II at end of issue.) Variation in the pattern of brain activation was found with the different paradigms. Significant local changes were observed in the temporal, posterior parietal, and frontal lobes. These local changes we correlated with specific task demands. Serial subtracting by seven resulted in a significant activation of Brodmann’s 37 area. This area involves the region about the superior and inferior temporal sulcus. This region has also been found activated in semantic verbal tasks (Vandenberghe et al., 1996). It is related to visual representation of words (Benson & Ardila, 1996). We may assume that the patient had adopted a semantic strategy to Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1516 B. Bernal et al. FIGURE 6. fMRI during abstract calculation. Color corresponds to voxels with p value less than .0005. Activation presented in yellow is located in the right PIPL. A wider cluster of activation is seen in the left middle frontal gyrus. The area of activation in the left precentral area is probably related to the left frontal eye field. The asymmetry of this finding suggests a cognitive involvement, since an underlying motor process would produce bilateral activation. (See Color Plate III at end of issue.) solving problems, consistent with his ability to approach an answer. Thus, the search for the answer was performed as a semantic word generation, i.e., to solve the problem “100 – 7 = __,” the patient’s strategy consisted of searching the nineties. Alternatively, the patient may have tried to visualize the numbers of the problems. The activation observed in the cuneus, along the transverse occipital sulcus, is interesting. Left cuneus activation has been described in sustained Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Acalculia and Brain Plasticity 1517 visual attention (Le et al., 1998). The patient may have used visual clues to perform the task such as picturing the numbers and scanning them into a given category. Precuneus activation has been observed in aphasia patients with improvement in verbal comprehension after training (Musso et al., 1999). The previous training of the patient may also partially explain these results. Activation of the middle frontal gyri has been reported already using this paradigm. This activation is felt to be related to working memory (Rueckert et al., 1996). The activation seen in the head of the right caudate nucleus, during basic calculation paradigm, was also observed in two cases in the control group. These results are in agreement with prior cases of acalculia reported in patients with subcortical strokes (Corbett et al., 1986). Basic calculations are automatic memory-related processes, which could be performed by subcortical structures. Therefore, it is understandable that our acalculia patient preserved the ability to perform simple basic calculations. Basic calculations (e.g., 5 + 2) represent kinds of verbal automatism. The lack of activation in the complex paradigm is not well understood; however, it is possible that the patient became frustrated and stopped performing the requested task. Abstract calculation paradigm produced left middle frontal gyrus, left frontal eye field, and right PIPL activation (in absence of the normal homologous contralateral area). The left middle frontal gyrus activation, as stated before, is related to verbal working memory, although pure (nonverbal) abstract tasks may elicit activation in the same regional (Roland & Friberg, 1985). The frontal eye field activation is probably related to pursuit and saccadic eye movements (Petit et al., 1997), and spatial short-term memory (Gaymard et al., 1999). However, the activation related to eye movement was not supported in a recent study (Gitelman et al., 2000), raising the possibility of an unknown role for this area in cognitive tasks. The asymmetry of activation supports this hypothesis. The right PIPL activation, in absence of the normal homologous contralateral area, during the abstract paradigm is the most striking finding of this case. The four normal subjects activated both PIPL, although the left PIPL was activated more strongly. Therefore, in our case, activation on the homologous contralateral area could be Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1518 B. Bernal et al. anticipated. The left angular gyrus cannot be activated because of encephalomalacia. The left PIPL, although preserved, did not show activation possibly due to disconnection from input areas, as suggested by the deep extension of the hypointensity representing gliosis of the white matter (Figure 1). The contralateral right-PIPL area is activated, with the left frontal networking that is intact. This may explain the patient’s abnormal performance indicating the inefficiency of this new hardwiring, or the remaining network. Activation of contralateral-homologous areas does not necessarily mean functional recovery. Asymmetric bilateral normal representation may explain previous results dealing with the shifting type of brain plasticity. Using different techniques, bilateral activation has been found in normal subjects involving basic unilateral motor tasks, sensory stimulation (Hansson & Brismar, 1999; Babiloni et al., 1999), and language tasks (Binder, 1997; Weiller, 1997). Unilateral activation, which does occur in many cases, may be also artificially obtained as a result of high threshold levels, which are usually applied to the image post-processing. Often, statistical analysis is done using very strict p values, therefore, eliminating areas of weaker activation. Conceivably, a left hemisphere lesion may appear to have contralateral activation if the same statistical methods are applied to a smaller sample with lower absolute values, or if less conservative p values are utilized to depict activation. This could give the appearance of shifting plasticity. There are no previous studies of brain plasticity in acalculia. Most previous reports of brain plasticity refer to language. However, language and calculation, as brain functions, share several features: they demand a network rather than a dedicated module, they are symbolic, and both are located principally in the left hemisphere. Therefore, some overlap in brain plasticity seems reasonable. Calculation and language functions are based on bilateral networks with several levels of complexity. Understanding the reorganization of the scheme of the network is more important than replacement of a function in the study of recovery of cognitive functions (Weiller et al., 1997). This is stated by Thulborn et al. (1999): “When a key node of a large-scale cortical network is damaged network components (namely, contralateral homologous) are increasingly recruited to increase their workload” (p. 753). Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. Acalculia and Brain Plasticity 1519 Bilateral temporal lobe activation has been elicited by verbal tasks, both in normal subjects and stroke patients (Binder, 1997). However, the right hemisphere activation in stroke patients was greater in areas contralateral to those found in normal subjects (Weiller et al., 1995; Weiller, 1998). Patients with left frontal strokes present initially with global metabolic reduction of the left hemisphere and new activation in the right frontal area homologous to Broca’s area, with repetition tasks. When recovery takes place, activation of the left posterior superior temporal gyrus returns, and the activation in the right frontal region (Broca’s homologue) disappears (Heiss et al., 1999). Temporal lesions show activation in the right temporal lobe in the early phase (without recovery) and later when recovery occurs (Heiss et al., 1999). The fact that right perisylvian areas in aphasic patients show stronger activation than in controls (Weiller et al., 1995) suggests the idea of a substitution role. This supports the assumption that the right hemisphere plays a crucial role in recovery, as suggested by some early PET studies (Ohyama et al., 1995; Price et al 1995). Clinical recovery is not only associated with the appearance of new activation in the right hemisphere, but also with the regression of functional depression in structurally unaffected regions of both hemispheres (Cappa et al., 1997). The recovery of the functional depression agrees with the demonstration that better language recovery occurs in individuals who have bilateral rather than right hemispherepredominant activation (Cao et al., 1999). These findings were also recently reported by Heiss et al. (1999) in a PET study. This group found that complete and satisfactory recovery from aphasia can only be achieved as long as structures of the left superior temporal gyrus are preserved and can be reintegrated into language processing and production. The final answer, however, is not fully known: Patients in speech therapy improve their performance on the Token test as their right superior temporal gyrus and left precuneus show increase in blood flow measures (Musso et al., 1999). These studies performed in aphasia patients may be useful in understanding our results in calculation. Many reported cases of aphasia patients also have acalculia. We feel that theoretical conclusions from one may be applied to the other. Our patient showed activation in the right PIPL area, the contra- Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. 1520 B. Bernal et al. lateral homologous area involved in calculations in normal subjects. However, he did not significantly recover from his deficit. The patient succeeded in some basic calculations because they represented automatic memory-related processes, somehow mediated by the right hemisphere. Basic calculations involving small numbers (e.g., adding and subtracting one-digit numbers) have been demonstrated dissociated from other types of calculations (Stanescu-Cosson et al., 2000; Cohen et al., 2000), because of having a domain-specific representation (Dehaene et al., 1998). Therefore, this type of calculation can be spared in primary acalculia, as was the case in our stroke patient. He possibly was also performing a spontaneous “cognitive prosthesis” (i.e., he may have been using an alternative semantic category strategy to approximate the results in serial subtracting by seven paradigm, explaining activation of Brodmann’s area 37, otherwise not seen in the control group). Combining extrapolated information obtained from language studies, and our observations in the normal subjects, we feel that the right PIPL activation represents the remaining activation of a subsidiary circuitry. This circuitry previously did subserve calculation, but now cannot accomplish the task utilizing only the right PIPL module. It may be assumed that the pattern of activation obtained corresponds to a redistribution of the workload over the pre-existing network, in which the right hemisphere was not crucial for calculation. This assumption has the support of previous reports in which biparietal activation was elicited in normal volunteers by calculation tasks (Chochon et al., 1999). Further investigations are needed to elucidate how redistribution is responsible for the so-called relocation and shifting phenomena, and if recovery is necessarily contingent upon these changes. CONCLUSION We present a case of acalculia in a patient with a left angular gyrus lesion, demonstrating on fMRI cortical activation related to mathematical tasks. The distribution of the obtained activation may be taken as brain “plasticity.” Findings taken from other functionalcognitive studies of language suggest a rewiring can occur without Acalculia and Brain Plasticity 1521 significant functional recovery. In some cases, the so-called rewiring is just the redistribution of workload in a pre-existent network which may not truly be plasticity. Int J Neurosci Downloaded from informahealthcare.com by University of North Carolina on 11/12/14 For personal use only. REFERENCES Babiloni, C., Carducci, F., Pizzella, V., Indovina, I., Romani, G. L., Rossini, P.M., & Babiloni, F. (1999). Bilateral neuromagnetic activation of human primary sensorimotor cortex in preparation and execution of unilateral voluntary finger movements. Brain Research, 827, 234–236. Benson, D. F., & Ardila, A. 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