Judith Law PhD

Judith Law


Publications:
2013
  Mechanisms for Stable, Robust, and Adaptive Development of Orientation Maps in the Primary Visual Cortex
Stevens, J-L, Law, J, Antolik, J & Bednar, JA 2013, 'Mechanisms for Stable, Robust, and Adaptive Development of Orientation Maps in the Primary Visual Cortex' Journal of Neuroscience, vol 33, no. 40, pp. 15747-15766. DOI: 10.1523/JNEUROSCI.1037-13.2013
Development of orientation maps in ferret and cat primary visual cortex (V1) has been shown to be stable, in that the earliest measurable maps are similar in form to the eventual adult map, robust, in that similar maps develop in both dark rearing and in a variety of normal visual environments, and yet adaptive, in that the final map pattern reflects the statistics of the specific visual environment. How can these three properties be reconciled? Using mechanistic models of the development of neural connectivity in V1, we show for the first time that realistic stable, robust, and adaptive map development can be achieved by including two low-level mechanisms originally motivated from single-neuron results. Specifically, contrast-gain control in the retinal ganglion cells and the lateral geniculate nucleus reduces variation in the presynaptic drive due to differences in input patterns, while homeostatic plasticity of V1 neuron excitability reduces the postsynaptic variability in firing rates. Together these two mechanisms, thought to be applicable across sensory systems in general, lead to biological maps that develop stably and robustly, yet adapt to the visual environment. The modeling results suggest that topographic map stability is a natural outcome of low-level processes of adaptation and normalization. The resulting model is more realistic, simpler, and far more robust, and is thus a good starting point for future studies of cortical map development.
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Stevens, Jean-Luc, Law, Judith, Antolik, Jan & Bednar, James A. .
Number of pages: 20
Pages: 15747-15766
Publication Date: 2 Oct 2013
Publication Information
Category: Article
Journal: Journal of Neuroscience
Volume: 33
Issue number: 40
ISSN: 0270-6474
Original Language: English
DOIs: 10.1523/JNEUROSCI.1037-13.2013
  Developing orientation maps using realistic patterns of lateral connectivity
Rudiger, P, Law, J, Antolik, J & Bednar, J 2013, 'Developing orientation maps using realistic patterns of lateral connectivity' 22nd Annual Computational Neuroscience Meeting: CNS 2013, Paris, France, 13/07/13 - 18/07/13, .
While developmental models have been very successful in replicating the main features of experimentally observed topographic maps in the primary visual cortex (V1), they have relied on several unrealistic assumptions. These models are typically variants of the self-organizing
map model [1], and almost universally assume “Mexicanhat” lateral connectivity in V1, with short-range excitatory and longer-range inhibitory connections. Experimental data is in direct conflict with this assumption, with anatomical tracing studies showing that neurons making long-range connections are excitatory [2,3]. A variety of
electrophysiological and psychophysical studies also suggest both excitatory and inhibitory effects at long ranges, depending on experimental conditions. The current consensus is that the actual pattern of connectivity consists of long-range excitation leading to di-synaptic inhibition via local inhibitory interneurons [2-4]. The
resulting aggregate circuit has an overall inhibitory effect when the excitatory drive to local inhibitory synapses is large enough. In principle, the behavior of this circuit at high input contrasts may therefore mimic the Mexican-hat profile of these earlier model, while potentially exhibiting more realistic contrast dependent behavior.

We present a rate-based model of simple-cell development that robustly self-organizes into biologically realistic orientation maps on the basis of this experimentally determined connectivity. The model is built using the Topographica simulator [5], and consists of a number of sheets of units representing the retinal photoreceptors, RGC/LGN
cells, and individual populations of excitatory and inhibitory V1 neurons. The receptive field weights, initialized randomly within a Gaussian envelope, are adjusted through Hebbian learning with divisive normalization in response to activity driven by 20,000 consecutive input
patterns (either natural images or artificial patterns). We show that development of realistic maps is robust, primarily due to homeostaticmechanisms in V1 and divisive contrast-gain control in the RGC/LGNlayer.

The model demonstrates that the experimentally established connectivity framework can lead to orderly map development and can replicate many of the contextual and contrast dependent effects observed in adult V1. This work looks at how Mexican-hat connectivity arises from the overall network interactions at high contrast and how
it adjusts at lower contrasts. Further, it demonstrates clearly how patchy long-range connectivity between isoorientation domains emerges, and the role it plays in modulating V1 activity. In doing so, the model provides a clear link between topographic map formation, the development of the underlying connectivity, and the perceptual consequences of this circuitry, including contrast-dependent
size-tuning shifts and the early stages of more complex effects like pop-out and contour completion.

In future, this work will help us to complete our understanding of the V1 circuit by adding feedback mechanisms or selectively modulating specific connections to model the effects of different neuromodulators. Additionally, the results may be used to provide realistic connectivity patterns for large scale spiking models, which often struggle to adequately constrain their connectivity. Overall, this model demonstrates for the first time that it is possible to robustly develop biologically plausible orientation maps on the basis of realistic connectivity, accounting for various surround modulation effects and providing a solid basis for future models of V1.

References

[1] Von der Malsburg, C.: Self-organization of orientation sensitive cells in the striate cortex. Kybernetik 1973, 14(2): 85–100

[2] Gilbert, D., & Wiesel, T.: Columnar specificity of intrinsic horizontal and corticocortical connections in cat visual cortex. The Journal of Neuroscience 1989, 9(7): 2432–2442.

[3] Hirsch, J. A, & Gilbert, C. D.: Synaptic physiology of horizontal connections in the cat’s visual cortex. The Journal of Neuroscience 1991, 11(6): 1800–9

[4] Weliky, M., Kandler, K., Fitzpatrick, D., & Katz, L. C. : Patterns of excitation and inhibition evoked by horizontal connections in visual cortex share a common relationship to orientation columns. Neuron 1995, 15(3): 541–52

[5] The Topographica Neural Map Simulator. [http://www.topographica.org]
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Rudiger, Philipp, Law, Judith, Antolik, Jan & Bednar, James.
Publication Date: 2013
Publication Information
Category: Poster
Original Language: English
2011
  Stable and robust development of orientation maps and receptive fields
Law, JS, Antolik, J & Bednar, JA 2011, 'Stable and robust development of orientation maps and receptive fields' BMC Neuroscience, vol 12, no. Suppl 1, pp. P10. DOI: 10.1186/1471-2202-12-S1-P10
General Information
Organisations: Neuroinformatics DTC.
Authors: Law, Judith S, Antolik, Jan & Bednar, James A.
Pages: P10
Publication Date: 1 Jan 2011
Publication Information
Category: Article
Journal: BMC Neuroscience
Volume: 12
Issue number: Suppl 1
ISSN: 1471-2202
Original Language: English
DOIs: 10.1186/1471-2202-12-S1-P10
2010
  Modeling the Emergence of Whisker Direction Maps in Rat Barrel Cortex
Wilson, SP, Law, J, Mitchinson, B, Prescott, TJ & Bednar, JA 2010, 'Modeling the Emergence of Whisker Direction Maps in Rat Barrel Cortex' PLoS One, vol 5, no. 1, e8778. DOI: 10.1371/journal.pone.0008778

Based on measuring responses to rat whiskers as they are mechanically stimulated, one recent study suggests that barrel-related areas in layer 2/3 rat primary somatosensory cortex (S1) contain a pinwheel map of whisker motion directions. Because this map is reminiscent of topographic organization for visual direction in primary visual cortex (V1) of higher mammals, we asked whether the S1 pinwheels could be explained by an input-driven developmental process as is often suggested for V1. We developed a computational model to capture how whisker stimuli are conveyed to supragranular S1, and simulate lateral cortical interactions using an established self-organizing algorithm. Inputs to the model each represent the deflection of a subset of 25 whiskers as they are contacted by a moving stimulus object. The subset of deflected whiskers corresponds with the shape of the stimulus, and the deflection direction corresponds with the movement direction of the stimulus. If these two features of the inputs are correlated during the training of the model, a somatotopically aligned map of direction emerges for each whisker in S1. Predictions of the model that are immediately testable include (1) that somatotopic pinwheel maps of whisker direction exist in adult layer 2/3 barrel cortex for every large whisker on the rat's face, even peripheral whiskers; and (2) in the adult, neurons with similar directional tuning are interconnected by a network of horizontal connections, spanning distances of many whisker representations. We also propose specific experiments for testing the predictions of the model by manipulating patterns of whisker inputs experienced during early development. The results suggest that similar intracortical mechanisms guide the development of primate V1 and rat S1.


General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Wilson, Stuart P., Law, Judith, Mitchinson, Ben, Prescott, Tony J. & Bednar, James A..
Keywords: (, , . )
Number of pages: 11
Publication Date: Jan 2010
Publication Information
Category: Article
Journal: PLoS One
Volume: 5
Issue number: 1
ISSN: 1932-6203
Original Language: English
DOIs: 10.1371/journal.pone.0008778
2009
  Homeostatic and gain control mechanisms in a developmental model of orientation map formation in V1
Law, J, Bednar, J & Antolik, J 2009, 'Homeostatic and gain control mechanisms in a developmental model of orientation map formation in V1' Computational and Systems Neuroscience (Cosyne) 2009, Salt Lake City, UT, United States, 26/02/09 - 3/03/09, . DOI: 10.3389/conf.neuro.06.2009.03.341
Numerous studies have shown that cortical neurons can self-regulate their response gain (i.e., their output in response to an input). Theoretical studies of such gain control have primarily considered single cells or small networks of neurons in the adult brain. However, gain control is likely to be particularly important during development, because the amount and distribution of input activity can change dramatically between neurogenesis and adulthood. For instance, the developing visual system at first receives intrinsically generated input, such as retinal waves or spontaneous cortical activity, and in later stages (after eye opening) receives direct visual stimulation from the environment. In this study we examine how gain control can interact with basic homeostatic mechanisms to reproduce the experimentally observed patterns of development in a large scale model of an orientation map in the primary visual cortex (V1). Using this model, we have identified a small set of mathematical rules that can reproduce the following experimentally observed phenomena: stable orientation map development (Chapman et al. J. Neurosci., 1996, 16:6443--6453), contrast independent orientation tuning (Alitto et al. J Neurophysiol., 2004 91:2797--2808), and orientation map development that is robust against changes in the levels or distributions of input activity over time (Crair et al. Science, 1998, 279:566--570). We show that the above constraints can be met by using a simple but plausible gain control mechanism at the level of the Lateral Geniculate Nucleus (LGN) or retina, plus a mechanism that maintains a constant ratio between the strength of different input types (afferent vs. feedback, and excitatory vs. inhibitory) to each individual neuron. By directly maintaining these specific interaction ratios, it is sufficient to use a simple threshold adjustment rule for each neuron, rather than the more complex intrinsic excitability adjustment rules previously designed for more abstract networks (Triesch ICANN, 2005, 65--70). This model thus highlights the benefit of studying these phenomena in neural models whose architecture is constrained by the known connectivity of neural structures (such as V1).
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Law, Judith, Bednar, James & Antolik, Jan.
Publication Date: 2009
Publication Information
Category: Poster
Original Language: English
DOIs: 10.3389/conf.neuro.06.2009.03.341
  Reconciling models of V1 development and adult function
Antolik, J, Law, JS & Bednar, J 2009, 'Reconciling models of V1 development and adult function' Society for Neuroscience Annual Meeting 2009, Chicago, United States, 17/10/09 - 21/10/09, .
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Antolik, Jan, Law, Judith S. & Bednar, James.
Publication Date: 2009
Publication Information
Category: Poster
Original Language: English
2007
  Homeostatic Plasticity in a Model of V1 Orientation Map Development.
Law, JS & Bednar, JA 2007, 'Homeostatic Plasticity in a Model of V1 Orientation Map Development.' Society for Neuroscience Annual Meeting, 2007, San Diego, California, United States, 3/11/07 - 7/11/07, .
Throughout the development of the map of orientation preference in primary visual cortex (V1), the statistics and strength of afferent inputs, synaptic strengths and sizes, and lateral connection patterns are all changing. It is therefore surprising that despite these massive changes, the orientation map develops with a remarkable stability in both orientation preference and orientation domain size (Chapman et al., 1996). It has been proposed that homeostatic mechanisms that automatically adjust the intrinsic excitability of neurons and/or multiplicatively scale synaptic strengths allow individual neurons to maintain stability of overall activity levels (Desai, 2003, Turrigiano and Nelson, 2004). We have explored the possibility that homeostatic plasticity also underlies the stability of map organization. Several homeostatic rules have been used to replace ad-hoc methods in simple self organizing map (SOM) models (e.g. Butko and Triesch, 2007, Sullivan and de Sa, 2006). However it still remains to be seen whether these rules will be sufficient in a more realistic model that includes adapting lateral connections. We propose a model that includes both homeostatic plasticity of intrinsic excitability and scaling of lateral connection strengths. In this way, a balance between activation due to afferent and lateral connection types is maintained. This model is the first to reproduce experimentally observed orientation map organization, selectivity , and stability despite changes in the input statistics.
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Law, Judith S. & Bednar, James A..
Publication Date: 2007
Publication Information
Category: Poster
Original Language: English
  Reconciling models of surround modulation and V1 feature map development
Law, JS & Bednar, JA 2007, 'Reconciling models of surround modulation and V1 feature map development' BMC Neuroscience, vol 8, no. Suppl 2, pp. S23. DOI: 10.1186/1471-2202-8-S2-S23
The cerebral cortex of mammals is organized as a set of topographic maps, forming sensory and motor areas such as those in the visual, auditory, and somatosensory systems. Understanding how these maps develop and whether they have any functional significance is critical for understanding cortical processing.

The prototypical example of topographic feature maps is the map of orientation preference in primary visual cortex (V1). Models of V1 orientation map development have been very successful in reproducing the features of biological maps. The majority of these models are based on a principle of "Mexican-hat" connectivity i.e. short-range excitatory and long-range inhibitory connections between neurons (e.g. [1]).

However, experimental data is in striking disagreement with this principle. There is a consensus that long-range connections between V1 neurons are excitatory [2]. Moreover, models with long-range excitatory connections are able to account for a wide range of experimental data from adult V1, such as surround modulation (e.g. [3]). Models of orientation map development are thus based on a connectivity which is precisely opposite to that suggested by a mounting body of experimental and computational evidence.

It is not yet clear if the circuits used in surround modulation models are consistent with the development of orientation maps. It is also important to consider how the topographic organization of orientation preference may affect surround modulation. Since cortical circuitry is intimately tied to topographic organization, it is likely that surround modulation properties differ depending on the position of a cell within the orientation map.

In order to address the above issues, we have developed the first model that is consistent with current models of surround modulation, yet also reproduces the features of successful developmental models of topographic map formation. The model consists of sheets of firing-rate-based units that represent the retina, LGN, excitatory, and inhibitory neurons in V1. An activity-driven Hebbian learning mechanism results in the adjustment of afferent (retina to V1) and long-range lateral connection weights (within V1), leading to the development of orientation selectivity organized smoothly in a realistic orientation map.

General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Law, Judith S & Bednar, James A.
Pages: S23
Publication Date: 1 Jan 2007
Publication Information
Category: Article
Journal: BMC Neuroscience
Volume: 8
Issue number: Suppl 2
ISSN: 1471-2202
Original Language: English
DOIs: 10.1186/1471-2202-8-S2-S23
2006
  Surround modulation by long-range lateral connections in an orientation map model of primary visual cortex development and function
Law, JS & Bednar, JA 2006, 'Surround modulation by long-range lateral connections in an orientation map model of primary visual cortex development and function' Society for Neuroscience 36th Annual Meeting (SfN), Atlanta, GA, United States, 14/10/06 - 18/10/06, .
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Law, Judith S. & Bednar, James A..
Publication Date: 2006
Publication Information
Category: Poster
Original Language: English

Projects:
Modelling species differences in visual system cortical maps (PhD)