Papers

The Calculating Brain: An fMRI Study

from Neuropsychologia 38 (2000), pp. 325-335

Abstract: To explore brain areas involved in basic numerical computation, functional magnetic imaging (fMRI) scanning was performed on college students during performance of three tasks; simple arithmetic, numerical magnitude judgment, and a perceptual- motor control task. For the arithmetic relative to the other tasks, results for all eight subjects revealed bilateral activation in Brodmann's area 44, in dorsolateral prefrontal cortex (areas 9 and 10), in inferior and superior parietal areas, and in lingual and fusiform gyri. Activation was stronger on the left for all subjects, but only at Brodmann's area 44 and the parietal cortices. No activation was observed in the arithmetic task in several other areas previously implicated for arithmetic, including the angular and supramarginal gyri and the basal ganglia. In fact, angular and supramarginal gyri were significantly deactivated by the verification task relative to both the magnitude judgment and control tasks for every subject. Areas activated by the magnitude task relative to the control were more variable, but in five subjects included bilateral inferior parietal cortex. These results confirm some existing hypotheses regarding the neural basis of numerical processes, invite revision of others, and suggest productive lines for future investigation. Published by Elsevier Science Ltd.

Download the paper here (pdf, 183 kB)


Appearances May Not Be Deceiving: Calculation Deficits due to Brain Structure Abnormality in Neurologically Normal Children

from Brain 124 (2001), pp. 1681-1682

Download the paper here, (pdf, 32 kB)


Investigating Cognitive Neuroplasticity in Single Cases: Lessons Learned from Applying Functional Neuroimaging Techniques to the Traditional Neuropsychological Case Study Framework

from Neurocase (2002) Vol. 8, pp. 355Ā|368

Abstract: We summarize two case studies as a context for discussing the use of neuroimaging as a convergent methodology in the study of neuroplasticity in single subjects. Throughout this paper we argue for a different approach for including neuroimaging in these types of study. Previous case studies of neuroplasticity in patients (ours as well as others reported elsewhere) have added neuroimaging to the traditional neuropsychological framework of comparing patient results with matched control groups, and synthesized results through descriptions of anatomical and behavioral dissociations. This type of approach is referred to as the comparison approach. We advocate a different approach that builds on findings from previous behavioral skill learning research. Specifically, we propose adding neuroimaging throughout learning or recovery of the ability of interest and making inferences from systematic changes in activation topography and intensity that occur within the context of predicted behavioral changes. We dub this approach the online approach. This approach should allow future investigators to circumvent many of the interpretation pitfalls that are common in comparison studies.

Download the paper here (pdf, 888 kB)


Category-Specific Representations of Social and Nonsocial Knowledge in the Human Prefrontal Cortex

from Journal of Cognitive Neuroscience (2003) 15:2, pp. 236Ā|248

Abstract: Complex social behavior and the relatively large size of the prefrontal cortex are arguably two of the characteristics that distinguish humans from other animals. Grafman presented a framework concerning how the prefrontal cortex (PFC) controls complex behavior using stored structured event complexes (SECs). We report behavioral and imaging data from a modified go/no-go paradigm in which subjects had to classify words (semantic) and phrases (SEC) according to category. In experimental trials, subjects classified items according to social or nonsocial activity; in control trials, they classified items according to font. Subjects were faster to classify social than nonsocial semantic items, with the reverse pattern evident for the social and nonsocial SEC items. In addition, the conditions were associated with different patterns of PFC activation. These results suggest that there are different psychological and neural substrates for social and nonsocial semantic and SEC representations.

Download the paper here (pdf, 220 kB)


Representation of Attitudinal Knowledge: Role of Prefrontal Cortex, Amygdala and Parahippocampal Gyrus

from Neuropsychologia 43 (2005), pp. 249Ā|259

Abstract: It has been proposed that behavior is influenced by representations of different types of knowledge: action representations, event knowledge, attitudes and stereotypes. Attitudes (representations of a concept or object and its emotional evaluation) allow us to respond quickly to a given stimulus. In this study, we explored the representation and inhibition of attitudes. We show that right dorsolateral prefrontal cortex mediates negative attitudes whereas left ventrolateral prefrontal cortex mediates positive attitudes. Parahippocampal regions and amygdala mediate evaluative processing. Furthermore, anxiety modulates right dorsolateral prefrontal activation during negative attitude processing. Inhibition of negative attitudes activates left orbitofrontal cortex: a region that when damaged is associated with socially inappropriate behavior in patients. Inhibition of positive attitudes activates a brain system involving right inferior frontal gyrus and bilateral anterior cingulate. Thus, we show that there are dissociable networks for the representation and inhibition of attitudes. Published by Elsevier Ltd.

Download the paper here, (pdf, 360 kB)

Verification of multiplication facts: An investigation using retrospective protocols

from American Journal of Psychology 119 (2006), pp. 87Ā|120

Retrospective verbal protocols collected throughout participants’ performance of a multiplication verification task (e.g., “7 ? 3 = 28, true or false?”) documented a number of different strategies and changes in strategy use across different problem categories used for this common experimental task. Correct answer retrieval and comparison to the candidate answer was the modal but not the only strategy reported. Experiment 1 results supported the use of a calculation algorithm on some trials and the use of the difference between the candidate and correct answers (i.e., split) on others. Experiment 2 clearly demonstrated that participants sometimes bypassed retrieval by relying on the split information. Implications for mental arithmetic theories and the general efficacy of retrospective protocols are discussed.

Download the paper here, (pdf, 286 kB)

Electrophysiological markers of skill-related neuroplasticity

from Biological Psychology 78 (2008), pp. 221|230

Neuroplasticity involved in acquiring a new cognitive skill was investigated with standard time domain event-related potentials (ERPs) of scalp-recorded electroencephalographic (EEG) activity and frequency domain analysis of EEG oscillations looking at the event-related synchronization (ERS) and desynchronization (ERD) of neural activity. Electroencephalographic activity was recorded before and after practice, while participants performed alphabet addition (i.e., E + 3 = G, true or false?). Participantís performance became automated with practice through a switch in cognitive strategy from mentally counting-up in the alphabet to retrieving the answer from memory. Time domain analysis of the ERPs revealed a prominent positive peak at 300 ms that was not reactive to problem attributes but was reduced with practice. A second prominent positive peak observed at 500 ms was found to be larger after practice, mainly for problems presented with correct answers. Frequency domain spectral analyses yielded two distinct findings: (1) a frontal midline ERS of theta activity that was greater after practice, and (2) a beta band ERD that increased with problem difficulty before, but not after practice. Because the EEG oscillations were not phase locked to the stimulus, they were viewed as being independent of the time domain results. Consequently, use of time and frequency domain analyses provides a more comprehensive account of the underlying electrophysiological data than either method alone. When used in combination with a well-defined cognitive/behavioral paradigm, this approach serves to constrain the interpretations of EEG data and sets a new standard for studying the neuroplasticity involved in skill acquisition.

Download the paper here, (pdf, 825 kB)

Glutamate is down-regulated and tinnitus loudness-levels decreased following rTMS over auditory cortex of the left hemisphere: A prospective randomized single-blinded sham-controlled cross-over study

from Hearing Research 358 (2018) pp 59|73

Using a prospective randomized single-blinded sham-controlled cross-over design, we studied the efficacy of low frequency (1-Hz) repetitive transcranial magnetic stimulation (rTMS) over auditory cortex of the left temporal lobe as an experimental treatment modality for noise-induced tinnitus. Pre/post outcome measures for sham vs. active rTMS conditions included differential changes in tinnitus loudness, self-perceived changes in the Tinnitus Handicap Questionnaire (THQ), and neurochemical changes of brain metabolite concentrations using single voxel proton magnetic resonance spectroscopy (1H-MRS) obtained from left and right auditory cortical areas. While no subject in our sample had complete abatement of their tinnitus percept, active but not sham rTMS significantly reduced the loudness level of the tinnitus perception on the order of 4.5 dB; improved subscales in several content areas on the THQ, and down regulated (reduced) glutamate concentrations specific to the auditory cortex of the left temporal lobe that was stimulated.
In addition, significant pair-wise correlations were observed among questionnaire variables, metab- olite variables, questionnaire-metabolite variables, and metabolite-loudness variables. As part of this correlation analysis, we demonstrate for the first time that active rTMS produced a down regulation in the excitatory neurotransmitter glutamate that was highly correlated (r ľ 0.77, p < 0.05) with a reduction in tinnitus loudness levels measured psychoacoustically with a magnitude estimation procedure. Overall, this study provides unique information on neurochemical, psychoacoustic, and questionnaire-related profiles which emphasizes the emerging fields of perceptual and cognitive MRS and provides a perspective on a new frontier in auditory and tinnitus-related research.

Download the paper here, (pdf, 3.3 MB)