Crizotinib in patients with tumors harboring ALK or ROS1 rearrangements in the NCI-MATCH trial

The NCI-MATCH was designed to characterize the efficacy of targeted therapies in histology-agnostic driver mutation-positive malignancies. Sub-protocols F and G were developed to evaluate the role of crizotinib in rare tumors that harbored either ALK or ROS1 rearrangements. Patients with malignancies that progressed following at least one prior systemic therapy were accrued to the NCI-MATCH for molecular profiling, and those with actionable ALK or ROS1 rearrangements were offered participation in sub-protocols F or G, respectively. There were five patients who enrolled on Arm F (ALK) and four patients on Arm G (ROS1). Few grade 3 or 4 toxicities were noted, including liver test abnormalities, and acute kidney injury. For sub-protocol F (ALK), the response rate was 50% (90% CI 9.8-90.2%) with one complete response among the 4 eligible patients. The median PFS was 3.8 months, and median OS was 4.3 months. For sub-protocol G (ROS1) the response rate was 25% (90% CI 1.3-75.1%). The median PFS was 4.3 months, and median OS 6.2 months. Data from 3 commercial vendors showed that the prevalence of ALK and ROS1 rearrangements in histologies other than non-small cell lung cancer and lymphoma was rare (0.1% and 0.4% respectively). We observed responses to crizotinib which met the primary endpoint for ALK fusions, albeit in a small number of patients. Despite the limited accrual, some of the patients with these oncogenic fusions can respond to crizotinib which may have a therapeutic role in this setting.

The growth of cognition: Free energy minimization and the embryogenesis of cortical computation

The assumption that during cortical embryogenesis neurons and synaptic connections are selected to form an ensemble maximising synchronous oscillation explains mesoscopic cortical development, and a mechanism for cortical information processing is implied by consistency with the Free Energy Principle and Dynamic Logic. A heteroclinic network emerges, with stable and unstable fixed points of oscillation corresponding to activity in symmetrically connected, versus asymmetrically connected, sets of neurons. Simulations of growth explain a wide range of anatomical observations for columnar and non-columnar cortex, superficial patch connections, and the organization and dynamic interactions of neurone response properties. An antenatal scaffold is created, upon which postnatal learning can establish continuously ordered neuronal representations, permitting matching of co-synchronous fields in multiple cortical areas to solve optimization problems as in Dynamic Logic. Fast synaptic competition partitions equilibria, minimizing "the curse of dimensionality", while perturbations between imperfectly partitioned synchronous fields, under internal reinforcement, enable the cortex to become adaptively self-directed. As learning progresses variational free energy is minimized and entropy bounded.

A new diminutive genus and species of catfish from Lake Tanganyika (Siluriformes: Clariidae)

The examination of material representing one of Lake Tanganyika's six previously recognized endemic catfish lineages, has revealed the presence of an additional genus of clariid, described here as Pseudotanganikallabes new genus. This genus is represented by a single species, Pseudotanganikallabes prognatha sp. nov., which is distinguished from all other clariids by its lack of an infraorbital series, the presence of multiple osseous connections between the swim bladder capsules and elements of the neurocranium, the absence of an ethmoid notch, the presence of a very large, egg-shaped occipital fontanelle and the extension of the lower lip beyond the margin of the upper jaw. A combination of additional external and molecular characters serves to further distinguish this taxon from all currently recognized clariid species. Phylogenetic analysis of mitochondrial (cytb) and nuclear (18S-ITS1-5.8S-ITS2-28S) sequence data supports the creation of a new genus for this species, as it appears to represent an independent, monophyletic lineage within the family Clariidae.

Sorafenib dose escalation is not uniformly associated with blood pressure elevations in normotensive patients with advanced malignancies

Hypertension with vascular endothelial growth factor (VEGF) receptor inhibitors is associated with superior treatment outcomes for advanced cancer patients. To determine whether increased doses of sorafenib cause incremental increases in blood pressure (BP) we measured 12-hour ambulatory BP in 41 normotensive advanced solid tumor patients in a randomized dose escalation study. After 7 days’ sorafenib (400mg BID) mean diastolic BP (DBP) increased in both study groups. After dose escalation, group A (400mg TID) had marginally significant further increase in 12-hour mean DBP (p=0.053) but group B (600mg BID) did not achieve statistically significant increases (p=0.25). Within groups, individuals varied in BP response to sorafenib dose escalation, but these differences did not correlate with changes in steady state plasma sorafenib concentrations. These findings in normotensive patients suggest BP is a complex pharmacodynamic biomarker of VEGF inhibition. Patients have intrinsic differences in sensitivity to the BP elevating effects of sorafenib.

Tolerance of full-dose sorafenib (S) combined with irinotecan (I; weekly, two on, one off) and cetuximab (C) in previously treated patients with advanced colorectal cancer (CRC)

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Background: The epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF) pathways are qualified targets in CRC, and are both inhibited by S. Preclinical evidence suggests S may also overcome cetuximab resistance. We previously reported (2008 GI Symposium, abstr#435) excessive toxicity of this combination with I 120 mg/m2 days (d) 1,8,15,22 every 42 d; the study was amended with an alternative I dose/schedule and the phase I results are presented.

Methods: Patients (pts) with advanced, pretreated CRC irrespective of KRAS mutation status with ECOG PS 0-2 and good organ function were eligible. The original dose/schedule of I was combined with C 400 mg/m2 IV d1 and 250 mg/m2 weekly; and S PO daily with dose level (DL) 1 = 200mg QD, DL2=200 mg BID and DL 3=400 mg BID. 2/4 pts had DLTs: grade (g) 3 fatigue and febrile neutropenia. The dose/schedule were amended to I 100 mg/m2 d1, 8 of 21d cycles (c) without changing S or C. As with the original design, there was a C/S lead-in for 2 weeks in c1, thus c1 (DLT window) was 5 weeks (w).

Results: In the original design, 5 subjects were recruited; after the study amendment, 13 additional pts were recruited (3, 3 and 7 pts respectively at amended DL1, DL2 and DL3). Overall, median age was 56.5 yrs, M: F 12:6 and colon: rectal cancer 16:2. All patients are evaluable and 3 are still on treatment (10+ - 20+ w). At the amended I dose/schedule, there were no further DLTs. Any c g3 toxicities included constitutional (fatigue:2, dehydration:1), gastrointestinal (nausea:1, vomiting:2, diarrhea:1), metabolic (hypomagnesemia:2 including one with tetany; hypokalemia:3), elevated ALT:1 and neutropenia:1. G 4 toxicities included neutropenia:1, thrombocytopenia:1. Two pts (one KRAS MT) had partial response with one pt (KRAS WT) on treatment for >44 w. 10 pts had stable disease (5–20+ w). PK/PD analysis is ongoing.

Conclusions: The recommended phase II dose is I 100 mg/m2d1,8; C 400 mg/m2 IV d1 and 250 mg/m2 weekly; and S 400 mg PO BID. The regimen is tolerable in advanced, pretreated CRC. Due to the limited responses and current phase III studies with S in CRC, there are no plans to open the phase II portion at this time.

No significant financial relationships to disclose.

Early results of a PMH Phase II Consortium trial of AZD0530 in advanced soft tissue sarcoma (STS)

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Background: AZD0530 is a novel oral anilino quinazoline that is selective for c-Src, c-Yes, Lck, and Bcr-Abl through ATP competitive and reversible inhibition of the target enzyme. Src kinases play a role in tumor cell migration, invasion and metastasis as well as being part of the signaling cascade for angiogenesis and growth factors. Advanced STS have limited therapeutic options; therefore we tested the efficacy of AZD0530 in advanced STS. Methods: The study utilized a Simon Two stage design with the primary endpoint be objective tumor response + prolonged stable disease rate (defined as partial/complete response by RECIST, or stable disease >4 months). Patients with measurable advanced STS with up to one prior chemotherapy for metastatic disease were eligible for study participation following informed consent. Patients were excluded for cardiac dysfunction, poorly controlled hypertension, inability to swallow or absorb medication. Patients had pulmonary function tests at baseline that were repeated within the first 4 weeks of therapy. Results: 17 patients (11 F, 6M) with advanced STS (leiomyosarcoma 5, rhabdomyosarcoma 3, MFH/carcinosarcoma/Fibrosarcoma 2, endometrial stromal sarcoma/liposarcoma/non-rhabdoSTS 1 each) were enrolled, the majority of whom had prior therapy (14 chemo and 9 xrt). Five continue on study. Nine discontinued therapy for progressive disease, 2 for toxicity and 1 patient request. Median time to progression in the 13 patients was 1.7 months. Possibly related severe adverse events (all grade 3) included fatigue (2), anemia/lymphopenia/hypokalemia (1 each). To date no confirmed responses have been seen. No drug related pulmonary toxicity has been observed. Conclusions: AZD0530 can be administered safely as a single agent in patients with a variety of advanced STS. To date, tumor responses have not been noted; however patients were not selected based on tumor target expression. Further testing may be warranted in selected tumors in combination with chemotherapy given pre-clinical synergy data or in tumors pre-selected for target expression.

No significant financial relationships to disclose.

A phase II trial of the proteasome inhibitor bortezomib in patients with recurrent or metastatic adenocarcinoma of the bile duct or gallbladder (NCI #6135)

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Background: There is currently no standard therapy for recurrent or metastatic cancers of the bile duct or gallbladder and available chemotherapy is of uncertain benefit. As activation of NF-κB has been described in these tumors, we initiated a phase II trial of the proteasome inhibitor bortezomib in patients with recurrent or metastatic disease. Methods: Patients with measurable metastatic or unresectable adenocarcinoma of the bile duct or gallbladder who had received up to 2 prior chemotherapy regimens were eligible. Other eligibility criteria included ECOG PS 0–2, total bilirubin ≤1.5X ULN, and ALT/AST ≤2.5 X ULN. Patients with baseline neuropathy ≥grade 2 were excluded. Bortezomib was administered at a dose of 1.3 mg/m2 as an intravenous bolus on days 1, 4, 8, and 11 of 21 day cycles with CT evaluation every 6 weeks. The primary endpoint was response rate. Null hypothesis: PR/CR≤5%. Alternative hypothesis: PR/CR ≥20%. 35 patients were required for 90% power with an early stopping rule at 20. Results: 20 patients were enrolled: 11M/9F, PS 0/1 (7/13), 6 gallbladder /14 bile duct. There was one patient with an unconfirmed partial response, 9 patients with stable disease, and 10 patients with progressive disease. Accrual was halted after 20 patients were enrolled as the early stopping rule for futility was met. Median PFS was 48 days (95% CI [32,124]) and median OS was 284 days (95% CI [155, 513]). Grade 3/4 toxicities were observed in 13 patients (65%), most commonly fatigue (4 patients), thrombocytopenia (3 patients), hyperbilirubinemia (3 patients), and hypotension (2 patients). Other SAEs at least possibly related to bortezomib included grade 3 vasculitis (1 patient) and grade 2 meningitis (1 patient). Conclusions: Bortezomib is not an active agent in the treatment of metastatic gallbladder or biliary tract cancer.

No significant financial relationships to disclose.

Phase II trial of the farnesyltransferase inhibitor tipifarnib plus fulvestrant in hormone receptor-positive metastatic breast cancer: New York Cancer Consortium Trial P6205

BACKGROUND

Fulvestrant produces a clinical benefit rate (CBR) of approximately 45% in tamoxifen-resistant, hormone receptor (HR)-positive metastatic breast cancer (MBC) and 32% in aromatase inhibitor (AI)-resistant disease. The farnesyltransferase inhibitor tipifarnib inhibits Ras signaling and has preclinical and clinical activity in endocrine therapy-resistant disease. The objective of this study was to determine the efficacy and safety of tipifarnib-fulvestrant combination in HR-positive MBC.

PATIENTS AND METHODS

Postmenopausal women with no prior chemotherapy for metastatic disease received i.m. fulvestrant 250 mg on day 1 plus oral tipifarnib 300 mg twice daily on days 1-21 every 28 days. The primary end point was CBR.

RESULTS

The CBR was 51.6% [95% confidence interval (CI) 34.0% to 69.2%] in 31 eligible patients and 47.6% (95% CI 26.3% to 69.0%) in 21 patients with AI-resistant disease. A futility analysis indicated that it was unlikely to achieve the prespecified 70% CBR. Tipifarnib dose modification was required in 8 of 33 treated patients (24%).

CONCLUSIONS

The target CBR of 70% for the tipifarnib-fulvestrant combination in HR-positive MBC was set too high and was not achieved. The 48% CBR in AI-resistant disease compares favorably with the 32% CBR observed with fulvestrant alone in prior studies and merit further clinical and translational evaluation.

Generation and control of cortical gamma: findings from simulation at two scales

A continuum model of electrocortical activity was applied separately at centimetric and macrocolumnar scales, permitting analysis of interaction between scales. State equations included effects of retrograde action potential propagation in dendritic trees, and kinetics of AMPA, GABA and NMDA receptors. Parameter values were provided from independent physiological and anatomical estimates. Realistic field potentials and pulse rates were obtained, including resonances in the alpha/theta and gamma ranges, 1/f(2) background activity, and autonomous gamma activity. Zero-lag synchrony and travelling waves occurred as complementary aspects of cortical transmission, and lead/lag relations between excitatory and inhibitory cell populations varied systematically around transition to autonomous gamma oscillation. Properties of the simulations can account for generation and control of gamma activity. All factors acting on excitatory/inhibitory balance controlled the onset and offset of gamma oscillation. Autonomous gamma was initiated by focal excitation of excitatory cells, and suppressed by laterally spreading trans-cortical excitation, which acted on both excitatory and inhibitory cell populations. Consequently, although spatially extensive non-specific reticular activation tended to suppress autonomous gamma, spatial variation of reticular activation could preferentially select fields of synchrony.

An outline of functional self-organization in V1: synchrony, STLR and Hebb rules

A model of self-organization of synapses in the striate cortex is described, and its functional implications discussed. Principal assumptions are: (a) covariance of cell firing declines with distance in cortex, (b) covariance of stimulus characteristics declines with distance in the visual field, and (c) metabolic rates are approximately uniform in all small axonal segments. Under these constraints, Hebbian learning implies a maximally stable synaptic configuration corresponding to anatomically and physiologically realistic ''local maps'', each of macro-columnar size, and each organized as Möbius projections of a "global map" of retinotopic form. Convergence to the maximally stable configuration is facilitated by the spatio-temporal learning rule. A tiling of V1, constructed of approximately mirror-image reflections of each local map by its neighbors, is formed. The model supplements standard concepts of feed-forward visual processing by introducing a new basis for contextual modulation and neural network identifications of visual signals, as perturbation of the synaptic configuration by rapid stimulus transients. On a long time-scale, synaptic development could overwrite the Möbius configuration, while LTP and LTD could mediate synaptic gain on intermediate time-scales.

Analysis of toxicity in a phase II study of sorafenib in soft tissue sarcoma (STS)

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Background: Sorafenib (BAY 43–9006) is an oral multi-targeted kinase inhibitor. Sorafenib causes dermatologic toxicity and hypertension, although the mechanisms are poorly understood. We observed significant toxicity requiring dose reductions in our phase II study of sorafenib in STS. Methods: 120 patients (40 M, 80 F; median age, 55 years) were treated between 10/05 and 12/06; accrual continues. All patients initially received sorafenib 400 mg BID. 118/120 registered patients were evaluable for toxicity. Clinical and laboratory variables were analyzed for association with dose reduction, using Kruskal-Wallis rank sum test for continuous variables and Fisher exact test for categorical variables. Variables significant at the p=0.05 level were further analyzed with a multivariate logistic regression model for their effects on dose reduction. Results: 53% of patients (63/118) required dose reductions, 53/63 for grade 2 or greater skin toxicity. Most common grade 3–4 drug-related toxicities included lymphopenia (14%), rash (12%), and hand-foot skin reaction (10%). Sex, height, weight, BSA and serum creatinine (Cr) were significantly associated with dose reduction by univariate analysis. Adjusting for sex and/or low serum Cr, BSA was not significantly associated with dose reduction. Sex and low serum Cr were borderline statistically significant predictors of dose reductions when both variables were included in a multivariate model. Only female sex remained a significant predictor when eliminating one outlier with BSA 2.83 (p=0.04). Conclusions: Female gender appears associated with skin toxicity, requiring dose reductions. Based on this multivariate analysis, a starting dose of 400 mg oral daily in women may limit side effects. Correlation with trough serum sorafenib levels is pending. This study is funded in part by NCI Grant P01-CA47179.

No significant financial relationships to disclose.

The maximum range and timing of excitatory contextual modulation in monkey primary visual cortex

Contextual modulations of receptive field properties by distal stimulus configurations have been shown for a variety of stimulus paradigms. A survey of excitatory contextual modulation data for V1 shows the maximum scale of interactions, measured in terms of distance in V1, to be between 10 mm and 30 mm. Different types of excitatory contextual modulation in V1 occur throughout the interval of 40-250 ms after stimulus delivery. This window provides opportunity for global propagation of visual contextual information to a subset of V1 neurons, via several routes within the visual system. We propose a number of experiments and analyses to confirm the results from this empirical survey.

Measurement of phase gradients in the EEG

Previous research has shown that spatio-temporal waves in the EEG are generally of long spatial wavelength and form smooth patterns of phase gradients at particular time-samples. This paper describes a method to measure smooth phase gradients of long spatial wavelength in the EEG. The method depends on the global pattern of phase at a given frequency and time and is therefore robust to variations, over time, in phase-lag between particular sites. Phases were estimated in the EEG signal using wavelet or short time-series Fourier methods. During an auditory oddball task, phases across the scalp tend to fall within a limited circular range, a range that is not indicative of phase-synchrony nor waves with multiple periods. At times the phases tended to maintain a spatially and temporally ordered relationship. The relative phases were analysed using three phase gradient basis functions, providing a measure of the amount of variance explained, across the electrodes, by smooth changes in relative phase from a single minimum or single maximum. The data from 586 adult subjects were analysed and it was found that the probability of phase gradient events varies with time and frequency in the stimulus-locked average, and with task demands. The temporal extent of spatio-temporal waves was measured by detecting smoothly changing patterns of phase latencies across the scalp. The specific spatial pattern and timing of phase gradients correspond closely to the latency distributions of certain ERPs.

Phase II study of sorafenib (BAY 43–9006) in combination with gemcitabine in recurrent epithelial ovarian cancer: A PMH phase II consortium trial

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Background: Sorafenib (BAY 43–9006; SOR) is a novel multi-targeted kinase inhibitor that targets the RAF/MEK/ERK signaling pathway, vascular endothelial growth factor (VEGF) receptor, platelet-derived growth factor receptor and flt-3. VEGFR is over-expressed in human ovarian tumors and this is associated with poor prognosis. Gemcitabine (GEM) is known to have single-agent activity in recurrent ovarian cancer (OC). A recent phase I study of GEM/SOR has demonstrated manageable toxicity and some objective responses in recurrent OC patients. We have designed a phase II trial to evaluate the efficacy of this novel combination in patients with recurrent OC. Methods: A two-stage, phase II clinical trial is underway for women with recurrent or refractory OC. Eligible patients may have received up to 2 prior lines of chemotherapy following recurrence, but must be GEM-naive. The treatment consists of SOR, 400mg PO bid continuously, in combination with GEM, IV weekly, 1000 mg/m2. Cycle 1 is an extended cycle of 7 weeks of GEM followed by a 1-week break. GEM is administered weekly for the first 3 weeks of each subsequent 4-week cycle. The primary endpoint is objective response rate, with response evaluated every 8 weeks. Results: 26 patients have been enrolled at 3 centers. 84 cycles have been administered (median 3; range 1–10). Median age was 57 (range: 37–77). 42% were ECOG PS 0 and 58% were PS 1. Of 18 patients evaluable for objective response, 1 patient had a confirmed PR by RECIST criteria and 5 patients had a confirmed PR by CA-125 criteria, yielding a combined RR of 33% in evaluable patients (RR by ITT = 23%). An additional 10 patients had SD. The median time to progression is 7.6 months (95% CI: 5.6-NA). 7 patients are inevaluable for objective response due to the following in cycle 1: withdrawal of consent (3), toxicity (2), and clinical PD (2). 1 patient on-study is yet to have a response evaluation. Grade 3 or 4 toxicities seen in more than 2 patients include: lymphopenia (8), thrombocytopenia (6), hypertension (3), hand-foot syndrome (3), pain (3), neutropenia (3) and hypokalemia (3). Conclusions: The preliminary results show encouraging activity with tolerable toxicity. This trial continues to accrue into a second stage.

No significant financial relationships to disclose.

Contribution of lateral interactions in V1 to organization of response properties

We propose a model of self-organization of synaptic connections in V1, emphasizing lateral interactions. Subject to Hebbian learning with decay, evolution of synaptic strengths proceeds to a stable state in which all synapses are either saturated, or have minimum pre/post-synaptic coincidence. The most stable configuration gives rise to anatomically realistic "local maps", each of macro-columnar size, and each organized as Mobius projections of retinotopic space. A tiling of V1, constructed of approximately mirror-image reflections of each local map by its neighbors is formed, accounting for orientation-preference singularities, linear zones, and saddle points-with each map linked by connections between sites of common orientation preference. Ocular dominance columns are partly explained as a special case of the same process. The occurrence of direction preference fractures always in odd numbers around singularities is a specific feature explained by the Mobius configuration of the local map. Effects of stimulus velocity, orientation relative to direction of motion, and extension, upon orientation preference, which are not accounted for by spatial filtering, are explained by interactions between the classic receptive field and global V1.

Neurophysical modeling of brain dynamics

A recent neurophysical model of brain electrical activity is outlined and applied to EEG phenomena. It incorporates single-neuron physiology and the large-scale anatomy of corticocortical and corticothalamic pathways, including synaptic strengths, dendritic propagation, nonlinear firing responses, and axonal conduction. Small perturbations from steady states account for observed EEGs as functions of arousal. Evoked response potentials (ERPs), correlation, and coherence functions are also reproduced. Feedback via thalamic nuclei is critical in determining the forms of these quantities, the transition between sleep and waking, and stability against seizures. Many disorders correspond to significant changes in EEGs, which can potentially be quantified in terms of the underlying physiology using this theory. In the nonlinear regime, limit cycles are often seen, including a regime in which they have the characteristic petit mal 3 Hz spike-and-wave form.

Simulated electrocortical activity at microscopic, mesoscopic, and global scales

Simulation of electrocortical activity requires (a) determination of the most crucial features to be modelled, (b) specification of state equations with parameters that can be determined against independent measurements, and (c) explanation of electrical events in the brain at several scales. We report our attempts to address these problems, and show that mutually consistent explanations, and simulation of experimental data can be achieved for cortical gamma activity, synchronous oscillation, and the main features of the EEG power spectrum including the cerebral rhythms and evoked potentials. These simulations include consideration of dendritic and synaptic dynamics, AMPA, NMDA, and GABA receptors, and intracortical and cortical/subcortical interactions. We speculate on the way in which Hebbian learning and intrinsic reinforcement processes might complement the brain dynamics thus explained, to produce elementary cognitive operations.

Development of synchronized activity of cranial motor neurons in the segmented embryonic mouse hindbrain

Spontaneous electrical activity synchronized among groups of related neurons is a widespread and important feature of central nervous system development. Among the many places from which spontaneous rhythmic activity has been recorded early in development are the cranial motor nerve roots that exit the hindbrain, the motor neuron pool that, at birth, will control the rhythmic motor patterns of swallow, feeding and the oral components of respiratory behaviour. Understanding the mechanism and significance of this hindbrain activity, however, has been hampered by the difficulty of identifying and recording from individual hindbrain motor neurons in living tissue. We have used retrograde labelling to identify living cranial branchiomeric motor neurons in the hindbrain, and [Ca2+]i imaging of such labelled cells to measure spontaneous activity simultaneously in groups of motor neuron somata. We find that branchiomeric motor neurons of the trigeminal and facial nerves generate spontaneous [Ca2+]i transients throughout the developmental period E9.5 to E11.5. During this two-day period the activity changes from low-frequency, long-duration events that are tetrodotoxin insensitive and poorly coordinated among cells, to high-frequency short-duration events that are tetrodotoxin sensitive and tightly coordinated throughout the motor neuron population. This early synchronization may be crucial for correct neuron-target development.

Unified neurophysical model of EEG spectra and evoked potentials

Evoked potentials -- the brain's transient electrical responses to discrete stimuli -- are modeled as impulse responses using a continuum model of brain electrical activity. Previous models of ongoing brain activity are refined by adding an improved model of thalamic connectivity and modulation, and by allowing for two populations of excitatory cortical neurons distinguished by their axonal ranges. Evoked potentials are shown to be modelable as an impulse response that is a sum of component responses. The component occurring about 100 ms poststimulus is attributed to sensory activation, and this, together with positive and negative feedback pathways between the cortex and thalamus, results in subsequent peaks and troughs that semiquantitatively reproduce those of observed evoked potentials. Modulation of the strengths of positive and negative feedback, in ways consistent with psychological theories of attentional focus, results in distinct responses resembling those seen in experiments involving attentional changes. The modeled impulse responses reproduce key features of typical experimental evoked response potentials: timing, relative amplitude, and number of peaks. The same model, with further modulation of feedback, also reproduces experimental spectra. Together, these results mean that a broad range of ongoing and transient electrocortical activity can be understood within a common framework, which is parameterized by values that are directly related to physiological and anatomical quantities.