4.    Note Payable Modification

In April 2011, the Company issued a $2,000,000 subordinated secured convertible note (“April 2011 Note”) to Brainlab AG (“Brainlab”). Upon issuance, the April 2011 Note was scheduled to mature in April 2016, unless earlier converted, and it accrued interest at the rate of 10% per year. The April 2011 Note was amended in February 2012, to among other things, provide Brainlab the option to convert the April 2011 Note into shares of the Company’s common stock at a conversion price of $0.60 per share at any time on or before February 23, 2013.

On February 21, 2013, Brainlab delivered notice to the Company of its election to convert the April 2011 Note into shares of the Company’s common stock at the conversion price of $0.60 per share. However, prior to the issuance of those conversion shares, on March 6, 2013, the Company and Brainlab entered into a loan modification. As a result of that loan modification, Brainlab revoked its election to convert the April 2011 Note into shares of common stock. Under the loan modification, the Company issued an amended and restated subordinated secured convertible note to Brainlab (the “Amended and Restated Note”), which amended the April 2011 Note (i) to remove the equity conversion feature, such that the Amended and Restated Note is not convertible into any shares of the Company’s capital stock, (ii) to reduce the interest rate, beginning March 6, 2013, from 10% per year to 5.5% per year, (iii) to ease certain restrictive loan covenants, and (iv) to reflect a new note principal balance of $4,289,444, which represents the sum of (A) the original principal balance of the April 2011 Note in the amount of $2,000,000, plus (B) interest accrued under the April 2011 Note through March 6, 2013 in the amount of $389,444, plus (C) $1,900,000. The Amended and Restated Note completely replaced and superseded the April 2011 Note. The Amended and Restated Note matures in April 2016, and principal and accrued interest under the Amended and Restated Note is payable in a single installment upon maturity. Like the April 2011 Note, the Amended and Restated Note is secured by a security interest in the assets of the Company, which security interest is junior and subordinate to the security interest that secures the related party convertible notes payable issued by the Company to Boston Scientific.

The Company has applied guidance in FASB ASC 470-50, “Debt Modifications and Extinguishments,” which requires calculating the fair value of the Amended and Restated Note, as of the loan modification date, based on the amended terms. At the time of the loan modification, the fair value of the Amended and Restated Note, with its principal balance of $4,289,444, was $3,745,621. The difference between the fair value of the Amended and Restated Note immediately following the loan modification and the carrying value of the April 2011 Note and related accrued interest immediately prior to the loan modification, resulted in a charge to other expense of $1,356,177 in the statement of operations during the nine months ended September 30, 2013. The $543,823 difference between the principal amount of the Amended and Restated Note and the fair value of the Amended and Restated Note on the date of the loan modification was recorded as a debt discount and is being amortized to interest expense using the effective interest method over the term of the Amended and Restated Note.