I finally discovered the right way to JSDoc object params:

@param {object} options A map of options to customize this SNS target
@param {string} options.accessKey An AWS account access key
@param {string} options.secretKey The secret key associated with the access key
[... yadda yadda ...]
@param {string} [options.region] The region housing the SNS topic in question. Default: "us-east-1".

Much much more readable :).