Bio

Bio


I began working at Stanford after obtaining my PhD in Neuroscience from the University of California, San Diego in 2011. My doctoral research investigated the neuroanatomical and neurophysiological correlates of word understanding abilities in healthy 1-2 year old infants, bilingual and hearing impaired adults. I am experienced using a range of human neuroimaging techniques including magneto and electro-encephalography as well as structural MRI techniques, including diffusion and quantitative MRI in pediatric populations.

I am most interested in studying the neural bases of language and reading skills in young children. Presently, I am applying advanced neuroimaging techniques, including diffusion and quantitative MRI, to examine how white matter structures of the brain contribute to reading and language skills in both healthy children and children born pre-term. Understanding both the neural and behavioral factors underlying these skills will help to identify children who are at greatest risk for learning difficulties. In later stages of this research, I will assist in developing and assessing interventional strategies for improving reading abilities in children at risk for delays.

Honors & Awards


  • Fine Science Tools Abstract Award, University of California, San Diego (2010)
  • Honorable Mention Graduate Research Fellowship Program, National Science Foundation (2007)
  • Post-baccalaureate Internship Training Award, National Institutes of Health (2004-2005)
  • Society for Neuroscience Travel Award, Faculty for Undergraduate Neuroscience (2003)
  • Arnold B Scheibel Neuroscience Award, Colorado College (2003)
  • First Place Research Presentation, Colorado-Wyoming Academy of Sciences (2003)
  • Distinction in Neuroscience, Colorado College (2003)
  • Phi Beta Kappa, Colorado College (2003)

Professional Education


  • Bachelor of Arts, Colorado College (2003)
  • Doctor of Philosophy, University of California San Diego (2011)

Stanford Advisors


Publications

Journal Articles


  • Independence of Early Speech Processing from Word Meaning CEREBRAL CORTEX Travis, K. E., Leonard, M. K., Chan, A. M., Torres, C., Sizemore, M. L., Qu, Z., Eskandar, E., Dale, A. M., Elman, J. L., Cash, S. S., Halgren, E. 2013; 23 (10): 2370-2379

    Abstract

    We combined magnetoencephalography (MEG) with magnetic resonance imaging and electrocorticography to separate in anatomy and latency 2 fundamental stages underlying speech comprehension. The first acoustic-phonetic stage is selective for words relative to control stimuli individually matched on acoustic properties. It begins ∼60 ms after stimulus onset and is localized to middle superior temporal cortex. It was replicated in another experiment, but is strongly dissociated from the response to tones in the same subjects. Within the same task, semantic priming of the same words by a related picture modulates cortical processing in a broader network, but this does not begin until ∼217 ms. The earlier onset of acoustic-phonetic processing compared with lexico-semantic modulation was significant in each individual subject. The MEG source estimates were confirmed with intracranial local field potential and high gamma power responses acquired in 2 additional subjects performing the same task. These recordings further identified sites within superior temporal cortex that responded only to the acoustic-phonetic contrast at short latencies, or the lexico-semantic at long. The independence of the early acoustic-phonetic response from semantic context suggests a limited role for lexical feedback in early speech perception.

    View details for DOI 10.1093/cercor/bhs228

    View details for Web of Science ID 000325760200009

    View details for PubMedID 22875868

  • Speech-Specific Tuning of Neurons in Human Superior Temporal Gyrus. Cerebral cortex (New York, N.Y. : 1991) Chan, A. M., Dykstra, A. R., Jayaram, V., Leonard, M. K., Travis, K. E., Gygi, B., Baker, J. M., Eskandar, E., Hochberg, L. R., Halgren, E., Cash, S. S. 2013

    Abstract

    How the brain extracts words from auditory signals is an unanswered question. We recorded approximately 150 single and multi-units from the left anterior superior temporal gyrus of a patient during multiple auditory experiments. Against low background activity, 45% of units robustly fired to particular spoken words with little or no response to pure tones, noise-vocoded speech, or environmental sounds. Many units were tuned to complex but specific sets of phonemes, which were influenced by local context but invariant to speaker, and suppressed during self-produced speech. The firing of several units to specific visual letters was correlated with their response to the corresponding auditory phonemes, providing the first direct neural evidence for phonological recoding during reading. Maximal decoding of individual phonemes and words identities was attained using firing rates from approximately 5 neurons within 200 ms after word onset. Thus, neurons in human superior temporal gyrus use sparse spatially organized population encoding of complex acoustic-phonetic features to help recognize auditory and visual words.

    View details for DOI 10.1093/cercor/bht127

    View details for PubMedID 23680841

  • Age-related Changes in Tissue Signal Properties Within Cortical Areas Important for Word Understanding in 12- to 19-Month-Old Infants. Cerebral cortex (New York, N.Y. : 1991) Travis, K. E., Curran, M. M., Torres, C., Leonard, M. K., Brown, T. T., Dale, A. M., Elman, J. L., Halgren, E. 2013

    Abstract

    Recently, our laboratory has shown that the neural mechanisms for encoding lexico-semantic information in adults operate functionally by 12-18 months of age within left frontotemporal cortices (Travis et al., 2011. Spatiotemporal neural dynamics of word understanding in 12- to 18-month-old-infants. Cereb Cortex. 8:1832-1839). However, there is minimal knowledge of the structural changes that occur within these and other cortical regions important for language development. To identify regional structural changes taking place during this important period in infant development, we examined age-related changes in tissue signal properties of gray matter (GM) and white matter (WM) intensity and contrast. T1-weighted surface-based measures were acquired from 12- to 19-month-old infants and analyzed using a general linear model. Significant age effects were observed for GM and WM intensity and contrast within bilateral inferior lateral and anterovental temporal regions, dorsomedial frontal, and superior parietal cortices. Region of interest (ROI) analyses revealed that GM and WM intensity and contrast significantly increased with age within the same left lateral temporal regions shown to generate lexico-semantic activity in infants and adults. These findings suggest that neurophysiological processes supporting linguistic and cognitive behaviors may develop before cellular and structural maturation is complete within associative cortices. These results have important implications for understanding the neurobiological mechanisms relating structural to functional brain development.

    View details for DOI 10.1093/cercor/bht052

    View details for PubMedID 23448869

  • Signed Words in the Congenitally Deaf Evoke Typical Late Lexicosemantic Responses with No Early Visual Responses in Left Superior Temporal Cortex JOURNAL OF NEUROSCIENCE Leonard, M. K., Ramirez, N. F., Torres, C., Travis, K. E., Hatrak, M., Mayberry, R. I., Halgren, E. 2012; 32 (28): 9700-9705

    Abstract

    Congenitally deaf individuals receive little or no auditory input, and when raised by deaf parents, they acquire sign as their native and primary language. We asked two questions regarding how the deaf brain in humans adapts to sensory deprivation: (1) is meaning extracted and integrated from signs using the same classical left hemisphere frontotemporal network used for speech in hearing individuals, and (2) in deafness, is superior temporal cortex encompassing primary and secondary auditory regions reorganized to receive and process visual sensory information at short latencies? Using MEG constrained by individual cortical anatomy obtained with MRI, we examined an early time window associated with sensory processing and a late time window associated with lexicosemantic integration. We found that sign in deaf individuals and speech in hearing individuals activate a highly similar left frontotemporal network (including superior temporal regions surrounding auditory cortex) during lexicosemantic processing, but only speech in hearing individuals activates auditory regions during sensory processing. Thus, neural systems dedicated to processing high-level linguistic information are used for processing language regardless of modality or hearing status, and we do not find evidence for rewiring of afferent connections from visual systems to auditory cortex.

    View details for DOI 10.1523/JNEUROSCI.1002-12.2012

    View details for Web of Science ID 000306526800027

    View details for PubMedID 22787055

  • Spatiotemporal Neural Dynamics of Word Understanding in 12- to 18-Month-Old-Infants CEREBRAL CORTEX Travis, K. E., Leonard, M. K., Brown, T. T., Hagler, D. J., Curran, M., Dale, A. M., Elman, J. L., Halgren, E. 2011; 21 (8): 1832-1839

    Abstract

    Learning words is central in human development. However, lacking clear evidence for how or where language is processed in the developing brain, it is unknown whether these processes are similar in infants and adults. Here, we use magnetoencephalography in combination with high-resolution structural magnetic resonance imaging to noninvasively estimate the spatiotemporal distribution of word-selective brain activity in 12- to 18-month-old infants. Infants watched pictures of common objects and listened to words that they understood. A subset of these infants also listened to familiar words compared with sensory control sounds. In both experiments, words evoked a characteristic event-related brain response peaking ∼400 ms after word onset, which localized to left frontotemporal cortices. In adults, this activity, termed the N400m, is associated with lexico-semantic encoding. Like adults, we find that the amplitude of the infant N400m is also modulated by semantic priming, being reduced to words preceded by a semantically related picture. These findings suggest that similar left frontotemporal areas are used for encoding lexico-semantic information throughout the life span, from the earliest stages of word learning. Furthermore, this ontogenetic consistency implies that the neurophysiological processes underlying the N400m may be important both for understanding already known words and for learning new words.

    View details for DOI 10.1093/cercor/bhq259

    View details for Web of Science ID 000293076300012

    View details for PubMedID 21209121

  • Spatial Organization of Neurons in the Frontal Pole Sets Humans Apart from Great Apes CEREBRAL CORTEX Semendeferi, K., Teffer, K., Buxhoeveden, D. P., Park, M. S., Bludau, S., Amunts, K., Travis, K., Buckwalter, J. 2011; 21 (7): 1485-1497

    Abstract

    Few morphological differences have been identified so far that distinguish the human brain from the brains of our closest relatives, the apes. Comparative analyses of the spatial organization of cortical neurons, including minicolumns, can aid our understanding of the functionally relevant aspects of microcircuitry. We measured horizontal spacing distance and gray-level ratio in layer III of 4 regions of human and ape cortex in all 6 living hominoid species: frontal pole (Brodmann area [BA] 10), and primary motor (BA 4), primary somatosensory (BA 3), and primary visual cortex (BA 17). Our results identified significant differences between humans and apes in the frontal pole (BA 10). Within the human brain, there were also significant differences between the frontal pole and 2 of the 3 regions studied (BA 3 and BA 17). Differences between BA 10 and BA 4 were present but did not reach significance. These findings in combination with earlier findings on BA 44 and BA 45 suggest that human brain evolution was likely characterized by an increase in the number and width of minicolumns and the space available for interconnectivity between neurons in the frontal lobe, especially the prefrontal cortex.

    View details for DOI 10.1093/cercor/bhq191

    View details for Web of Science ID 000291750400003

    View details for PubMedID 21098620

  • Language Proficiency Modulates the Recruitment of Non-Classical Language Areas in Bilinguals PLOS ONE Leonard, M. K., Torres, C., Travis, K. E., Brown, T. T., Hagler, D. J., Dale, A. M., Elman, J. L., Halgren, E. 2011; 6 (3)

    Abstract

    Bilingualism provides a unique opportunity for understanding the relative roles of proficiency and order of acquisition in determining how the brain represents language. In a previous study, we combined magnetoencephalography (MEG) and magnetic resonance imaging (MRI) to examine the spatiotemporal dynamics of word processing in a group of Spanish-English bilinguals who were more proficient in their native language. We found that from the earliest stages of lexical processing, words in the second language evoke greater activity in bilateral posterior visual regions, while activity to the native language is largely confined to classical left hemisphere fronto-temporal areas. In the present study, we sought to examine whether these effects relate to language proficiency or order of language acquisition by testing Spanish-English bilingual subjects who had become dominant in their second language. Additionally, we wanted to determine whether activity in bilateral visual regions was related to the presentation of written words in our previous study, so we presented subjects with both written and auditory words. We found greater activity for the less proficient native language in bilateral posterior visual regions for both the visual and auditory modalities, which started during the earliest word encoding stages and continued through lexico-semantic processing. In classical left fronto-temporal regions, the two languages evoked similar activity. Therefore, it is the lack of proficiency rather than secondary acquisition order that determines the recruitment of non-classical areas for word processing.

    View details for DOI 10.1371/journal.pone.0018240

    View details for Web of Science ID 000288811500031

    View details for PubMedID 21455315

  • Spatiotemporal dynamics of bilingual word processing NEUROIMAGE Leonard, M. K., Brown, T. T., Travis, K. E., Gharapetian, L., Hagler, D. J., Dale, A. M., Elman, J. L., Halgren, E. 2010; 49 (4): 3286-3294

    Abstract

    Studies with monolingual adults have identified successive stages occurring in different brain regions for processing single written words. We combined magnetoencephalography and magnetic resonance imaging to compare these stages between the first (L1) and second (L2) languages in bilingual adults. L1 words in a size judgment task evoked a typical left-lateralized sequence of activity first in ventral occipitotemporal cortex (VOT: previously associated with visual word-form encoding) and then ventral frontotemporal regions (associated with lexico-semantic processing). Compared to L1, words in L2 activated right VOT more strongly from approximately 135 ms; this activation was attenuated when words became highly familiar with repetition. At approximately 400 ms, L2 responses were generally later than L1, more bilateral, and included the same lateral occipitotemporal areas as were activated by pictures. We propose that acquiring a language involves the recruitment of right hemisphere and posterior visual areas that are not necessary once fluency is achieved.

    View details for DOI 10.1016/j.neuroimage.2009.12.009

    View details for Web of Science ID 000274064500039

    View details for PubMedID 20004256

  • Somatodendritic Kv7/KCNQ/M channels control interspike interval in hippocampal interneurons JOURNAL OF NEUROSCIENCE Lawrence, J. J., Saraga, F., Churchill, J. F., Statland, J. M., Travis, K. E., Skinner, F. K., McBain, C. J. 2006; 26 (47): 12325-12338

    Abstract

    The M-current (I(M)), comprised of Kv7 channels, is a voltage-activated K+ conductance that plays a key role in the control of cell excitability. In hippocampal principal cells, I(M) controls action potential (AP) accommodation and contributes to the medium-duration afterhyperpolarization, but the role of I(M) in control of interneuron excitability remains unclear. Here, we investigated I(M) in hippocampal stratum oriens (SO) interneurons, both from wild-type and transgenic mice in which green fluorescent protein (GFP) was expressed in somatostatin-containing interneurons. Somatodendritic expression of Kv7.2 or Kv7.3 subunits was colocalized in a subset of GFP+ SO interneurons, corresponding to oriens-lacunosum moleculare (O-LM) cells. Under voltage clamp (VC) conditions at -30 mV, the Kv7 channel antagonists linopirdine/XE-991 abolished the I(M) amplitude present during relaxation from -30 to -50 mV and reduced the holding current (I(hold)). In addition, 0.5 mM tetraethylammonium reduced I(M), suggesting that I(M) was composed of Kv7.2-containing channels. In contrast, the Kv7 channel opener retigabine increased I(M) amplitude and I(hold). When strongly depolarized in VC, the linopirdine-sensitive outward current activated rapidly and comprised up to 20% of the total current. In current-clamp recordings from GFP+ SO cells, linopirdine induced depolarization and increased AP frequency, whereas retigabine induced hyperpolarization and arrested firing. In multicompartment O-LM interneuron models that incorporated I(M), somatodendritic placement of Kv7 channels best reproduced experimentally measured I(M). The models suggest that Kv3- and Kv7-mediated channels both rapidly activate during single APs; however, Kv3 channels control rapid repolarization of the AP, whereas Kv7 channels primarily control the interspike interval.

    View details for DOI 10.1523/JNEUROSCI.3521-06.2006

    View details for Web of Science ID 000242387800026

    View details for PubMedID 17122058

  • Regional dendritic variation in neonatal human cortex: A quantitative Golgi study DEVELOPMENTAL NEUROSCIENCE Travis, K., Ford, K., Jacobs, B. 2005; 27 (5): 277-287

    Abstract

    The present study quantitatively compared the basilar dendritic/spine systems of lamina V pyramidal neurons across four hierarchically arranged regions of neonatal human neocortex. Tissue blocks were removed from four Brodmann's areas (BAs) in the left hemisphere of four neurologically normal neonates (mean age=41+/- 40 days): primary (BA4 and BA3-1-2), unimodal (BA18), and supramodal cortices (BA10). Tissue was stained with a modified rapid Golgi technique. Ten cells per region (N=160) were quantified. Despite the small sample size, significant differences in dendritic/spine extent obtained across cortical regions. Most apparent were substantial differences between BA4 and BA10: total dendritic length was 52% greater in BA4 than BA10, and dendritic spine number was 67% greater in BA4 than BA10. Neonatal patterns were compared to adult patterns, revealing that the relative regional pattern of dendritic complexity in the neonate was roughly the inverse of that established in the adult, with BA10 rather than BA4 being the most complex area in the adult. Overall, regional dendritic patterns suggest that the developmental time course of basilar dendritic systems is heterochronous and is more protracted for supramodal BA10 than for primary or unimodal regions (BA4, BA3-1-2, BA18).

    View details for DOI 10.1159/000086707

    View details for Web of Science ID 000231701800001

    View details for PubMedID 16137985

Stanford Medicine Resources: